P1133 Upstream O2 Sensor Diagnostics

mngopher22

Original poster
Member
Aug 28, 2012
20
I keep getting P1133 and P0136 DTC codes on my 2004 Chevy trailblazer with I6 engine. Originally I went to autozone and got a bosch. Yes i know get ac delco. Then i bought AC delco one from rockauto, and that is what is currently in the vehicle. I finally got motivated enough to do some in depth digging into the issue at hand. I am an EE so I used an oscilloscope to measure the upstream o2 sensor data in real time. I also have a OBD tool but you can't resolution as good as you can with an scope. Below I have posted the testing of 2 different upstream o2 sensors at idle and at 2000RPM.

Major question I have is how fast should the o2 sensor be switching from rich to lean at idle and at 2000rpm? From these graphs at idle its switching at 0.2Hz and at 2000rpm is switching at 0.5Hz. How fast should these be switching on a trailblazer? Any help would be greatly appreciated! Thanks


1st picture is bosch sensor at idle
2nd picture is bosch at 2000rpm
3rd picture is ac delco at idle
4th picture is ac delco at 2000rpm
5th picture is heater circuit
 

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The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
WELCOME COMRADE!!!!! I'm a EE, and have been volunteering on trailvoy, then GMTN, for 7 years now, and you're the first poster to ever show scope shots!!!!! You probably don't need to have the term PWM explained, either. :wink:

Those are horribly slow transitions. O2 sensors should run at 1 Hz or faster. When I put in a new one, it was about 1.5 Hz if I remember correctly. If you have a new sensor, then something else is slowing down the control loop. A dirty throttle body would give you an erratic idle as the AC compressor cycles on and off, and you would probably have mentioned that. But depending on your mileage, it may be a good thing to do anyway. Many of us do it every 30K.

But the throttle plate isn't involved in the quick transitions, I don't think. Probably fuel injector pulse width and duty cycle. My experience is that it's usually a bad O2 sensor, but if your Delco is new, I'd start by looking at the Fuel Trim numbers to see if you have an injector issue (could benefit by running injector cleaner and/or a Seafoam treatment) or a vacuum leak. Loose hoses and especially loose intake manifold bolts are a common problem.

How did you find us, by the way, after we all left Trailvoy last December?
 

mngopher22

Original poster
Member
Aug 28, 2012
20
Roadie, I tracked you down frankly because I know you know what your talking about and I think you could help me figure out my issue.
I used your advice a long time back to diagnose and replace a coil pack and wheel bearing hub assembly and I am eternally grateful.
Yes I know what PWM is. :smile:
I don't understand why the heater circuit picture i posted above doesn't have constant duty cycle. Very strange to me but hey maybe thats the way PCM's do it. The throttle body is as clean as a whistle and I have been doing that maintenance item every 10k or so again due to your advice a while back on trailvoy.

On diagnosing my problem, we can rule out electrical issues because i see the exact same waveforms with the scope as I do using my OBD scan tool, therefore i know all the data is getting to the PCM. Second thing I have noticed recently is my temp gauge sits 1 to 2 ticks to the left of 210 on my dash. On the drive home today I am going to log, using the OBD tool, the collant temperature during my whole drive. I am want to make sure that i know if ECT/ thermostat are good or bad.

Is there any more waveforms or data I can extract to aid in the diagnoses of this issue? I can get about anything you need.

Also below I am going to post some O2 postcat sensor data that i have extracted via obd tool from a couple drives to and from work.
 

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The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Didn't know you had been stalking me. Cool. :rotfl:

That post-cat data is fine. It proves the cat is working to smooth the combustion byproducts. I had a mechanically damaged cat and got the code for "Low Cat Efficiency" and the post cat data looked just like the pre cat data so it was easy to diagnose. Not cheap to fix, being in CA and all that. We MUST use OEM cats - no aftermarket stuff has been qualified by CARB.

I had no idea the heater was even left on after the PCM went into closed loop mode. The exhaust should heat it well enough, I thought. Maybe not at idle or in deceleration when there's no fuel being burned. Anyway, no harm. Can't understand the design constraints of EVERY possible system in the bloody vehicle. :frown:

Wish you had mentioned the ECT in the first post. :undecided: That may be messing with your mixture, AFR, and starting to clog your cat if not fixed. And if the sensor is telling the truth. Again, the fuel trim numbers would help confirm the hypothesis.

When I lived in Massachusetts, we used to camp south of Bath on Small Point every August for 20 years. I know Maine pretty well. What's a EE doing in Bangor?
 

mngopher22

Original poster
Member
Aug 28, 2012
20
Do you want both my long term and short term fuel trims plotted for my drive home? I can also do engine coolant temp to show you.
When I lived in Massachusetts, we used to camp south of Bath on Small Point every August for 20 years. I know Maine pretty well. What's a EE doing in Bangor?
I took a job at the university out here
 

RayVoy

Member
Nov 20, 2011
939
Hey Guys, I'm not an expert on O2's, but it is my understanding, that the mixture drives the voltage pulses. The faster the pulse rate, the more efficient is the complete fuel system.

Obviously, looking at the scope, some sensors are faster than others.

As the fuel ratio goes rich, the oxygen content decreases, causing an increase in voltage, a corresponding voltage decrease occurs when the mix goes lean (oxygen content increases). Monitoring the voltage fluctuations, the PCM corrects the pulse width of the injectors (the monitoring and correction is faster with direct injection, compared to single tb injection)

So, the conclusion, the faster the PCM adjusts the injector pulse width, the faster the O2 sensor pulses (at least, to the extent of it's sensitivity).

The heater pulse, I don't know. I do know, it likes to be around 600 deg F, I would think it would shut off at the desired temp. I do know the coolant temp is a big factor in keeping the O2 sensor in the "closed loop" (operating) mode. There is a possibility, low engine temp may cause the duty cycle to pulse. There is also a possibility, that is the way it should operate.
 

mngopher22

Original poster
Member
Aug 28, 2012
20
Do you want both my long term and short term fuel trims plotted for my drive home? I can also do engine coolant temp to show you.
Long story short, I got in my vehicle tonight and the stupid obd adapter decided not to work tonight. Ill take a look at it at work tommorrow and hopefully and the drive home I can get some fuel trim data and engine coolant temp.
 

Wooluf1952

Member
Nov 20, 2011
2,663
Milwaukee, Wisconsin
mngopher22 said:
Long story short, I got in my vehicle tonight and the stupid obd adapter decided not to work tonight. Ill take a look at it at work tommorrow and hopefully and the drive home I can get some fuel trim data and engine coolant temp.

Check fuse #13 in the under hood fuse box. That powers the OBD connection.
 

mngopher22

Original poster
Member
Aug 28, 2012
20
Wooluf1952 said:
Check fuse #13 in the under hood fuse box. That powers the OBD connection.

Thanks, thats not it because the OBD adapter powers up fine, its just because its a cheap ebay adapter and its very finicky! :eek:
 

mngopher22

Original poster
Member
Aug 28, 2012
20
JerryIrons said:
Do you have a leak in your exhaust system ? (before sensor)

Yah a while back that was the first suggestion and I looked all over the exhaust manifold and I didn't find a leak.
 

BRomanJr

Member
Dec 9, 2011
371
RayVoy said:
Hey Guys, I'm not an expert on O2's, but it is my understanding, that the mixture drives the voltage pulses. The faster the pulse rate, the more efficient is the complete fuel system.

Obviously, looking at the scope, some sensors are faster than others.

As the fuel ratio goes rich, the oxygen content decreases, causing an increase in voltage, a corresponding voltage decrease occurs when the mix goes lean (oxygen content increases). Monitoring the voltage fluctuations, the PCM corrects the pulse width of the injectors (the monitoring and correction is faster with direct injection, compared to single tb injection)

So, the conclusion, the faster the PCM adjusts the injector pulse width, the faster the O2 sensor pulses (at least, to the extent of it's sensitivity).

The heater pulse, I don't know. I do know, it likes to be around 600 deg F, I would think it would shut off at the desired temp. I do know the coolant temp is a big factor in keeping the O2 sensor in the "closed loop" (operating) mode. There is a possibility, low engine temp may cause the duty cycle to pulse. There is also a possibility, that is the way it should operate.


In my experience, the O2 sensor build quality, operating temperature and overall health affects the switching speed, the PCM only responds to changing signals from the O2 sensor and the PCM is clocked faster than the O2 can switch.

That's why we call sensors "lazy" as they age or become defective. So any speed discrepancy is the function/fault of the sensor.
 

mngopher22

Original poster
Member
Aug 28, 2012
20
I am going to try again tonight to get fuel trims and engine collant temp on the way home. In preparation for replacing the thermostat and ECT sensor, I want to make sure I am looking at the right parts.

Is the correct thermostat for a 2004 I6 Chevy trailblazer part number 1511006 from rockauto?

Is the correct ECT sensor for a 2004 I6 Chevy trailblazer part number 213963 from rockauto?

Is the correct upstream O2 sensor for a 2004 I6 Chevy trailblazer part number 21054 from rockauto?
I bought an AC Delco from them and when the part came it was stamped NTK on the oxygen sensor.

Is the correct downstream O2 sensor for a 2004 I6 Chevy trailblazer part number 21044 from rockauto?
 

BRomanJr

Member
Dec 9, 2011
371
mngopher22 said:
I am going to try again tonight to get fuel trims and engine collant temp on the way home. In preparation for replacing the thermostat and ECT sensor, I want to make sure I am looking at the right parts.

Is the correct thermostat for a 2004 I6 Chevy trailblazer part number 1511006 from rockauto?

Is the correct ECT sensor for a 2004 I6 Chevy trailblazer part number 213963 from rockauto?

Is the correct upstream O2 sensor for a 2004 I6 Chevy trailblazer part number 21054 from rockauto?
I bought an AC Delco from them and when the part came it was stamped NTK on the oxygen sensor.

Is the correct downstream O2 sensor for a 2004 I6 Chevy trailblazer part number 21044 from rockauto?


If you haven't purchased it already, Save some money, The Downstream sensor (used for calculating CAT health) only needs to be replaced when a code sets for that problem, It will NOT affect drive-ability or gas mileage.
 

mngopher22

Original poster
Member
Aug 28, 2012
20
BRomanJr said:
In my experience, the O2 sensor build quality, operating temperature and overall health affects the switching speed, the PCM only responds to changing signals from the O2 sensor and the PCM is clocked faster than the O2 can switch.

That's why we call sensors "lazy" as they age or become defective. So any speed discrepancy is the function/fault of the sensor.

I just want to understand what is meant by lazy. I have read a lot about o2 sensors and have seen the term lazy to describe a sensor thrown around a lot. From what I have read when the magnitude is less ie its not switching from .1V to .9V that has been described as lazy. In my waveforms though it switches from .1V to .9V but the cycle frequency is very slow. Its happening at .2 - .5Hz. Would you define a slower switching frequency as a lazy sensor? or would you describe an attenuated sensor signal as lazy? or would you describe a lazy sensor as a sensor that takes more than 100ms to transition from rich to lazy?
 

BRomanJr

Member
Dec 9, 2011
371
mngopher22 said:
I just want to understand what is meant by lazy. I have read a lot about o2 sensors and have seen the term lazy to describe a sensor thrown around a lot. From what I have read when the magnitude is less ie its not switching from .1V to .9V that has been described as lazy. In my waveforms though it switches from .1V to .9V but the cycle frequency is very slow. Its happening at .2 - .5Hz. Would you define a slower switching frequency as a lazy sensor? or would you describe an attenuated sensor signal as lazy? or would you describe a lazy sensor as a sensor that takes more than 100ms to transition from rich to lazy?

Lazy, is slow switching, I have rarely seen attenuated range, usually just before the sensor fails.
What speed is too slow, I don't know what that Hz/ms would be, I just compare my experience with new/good sensor speeds and take note when they are much slower. There probably is a threshold to decide between good and bad, I just don't know it.

Spending too much time with excess fuel, or not enough fuel makes the engine run rough (rich) or misfiring (lean). both conditions can cause a rich smelling exhaust. Slow (lazy) O2 sensors fool a lot of mechanics.
 

mngopher22

Original poster
Member
Aug 28, 2012
20
BRomanJr said:
Lazy, is slow switching, I have rarely seen attenuated range, usually just before the sensor fails.
What speed is too slow, I don't know what that Hz/ms would be, I just compare my experience with new/good sensor speeds and take note when they are much slower. There probably is a threshold to decide between good and bad, I just don't know it.

Spending too much time with excess fuel, or not enough fuel makes the engine run rough (rich) or misfiring (lean). both conditions can cause a rich smelling exhaust. Slow (lazy) O2 sensors fool a lot of mechanics.

Still trying to understand lazy, do you mean slow switching frequency ie the amount of times it switches from rich to lean and lean to rich in say 1 second? Or do you mean how long it takes to transition from lean to rich?


On a happy note, I found that during some previous drives home I captured some engine coolant temp sensor data via OBD logger. I have plotted a couple trips for you guys to look over. From what I see even though I am not throwing a code right now for thermostat, I should change both the thermostat and ECT sensor. Would the experts on here agree?
 

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BRomanJr

Member
Dec 9, 2011
371
mngopher22 said:
Still trying to understand lazy, do you mean slow switching frequency ie the amount of times it switches from rich to lean and lean to rich in say 1 second? Or do you mean how long it takes to transition from lean to rich?

Slow switching or long transition is the same thing, if it takes too long for the sensor to react to mixture changes from the computer it is lazy.


mngopher22 said:
On a happy note, I found that during some previous drives home I captured some engine coolant temp sensor data via OBD logger. I have plotted a couple trips for you guys to look over. From what I see even though I am not throwing a code right now for thermostat, I should change both the thermostat and ECT sensor. Would the experts on here agree?

If the Thermostat fails and keeps your temps low, a working ECT Sensor could be putting out accurate readings, and your mileage may suffer.

If the ECT sensor is defective it can report the wrong temp even though the thermostat is working flawlessly. In this case the PCM "thinks" it is running cold (or hot) and your mileage may suffer.

A definitive test is to measure the coolant temp (another sensor inserted in the coolant or a non-contact temperature device) at the thermostat and match it to an OBDII reading.

So most folks just change both based on cost and installation difficulty.
 

The_Roadie

Lifetime VIP Donor
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Nov 19, 2011
9,957
Portland, OR
Those ECT charts look OK.

Slow sensor means slow repetition rate from rising edge to rising edge. The risetime of the edges is not looked at.

Physically, the reason they get slow is that the zirconium dioxide sensor had ambient air on one side, and the other is exposed to the exhaust gasses, but it's protected by a screen with slots or holes. The holes get clogged with carbon and the exhaust gas flow into the sensor chamber is restricted. So the response of the control loop is delayed by the sensor and the loop slows down. It's like having a logic chain in a control loop with one IC changing its propagation delay from 5nS to 500mS. (I thought i would NEVER use that analogy in an auto forum!)
 

mngopher22

Original poster
Member
Aug 28, 2012
20
the roadie said:
Those ECT charts look OK.

Slow sensor means slow repetition rate from rising edge to rising edge. The risetime of the edges is not looked at.

Physically, the reason they get slow is that the zirconium dioxide sensor had ambient air on one side, and the other is exposed to the exhaust gasses, but it's protected by a screen with slots or holes. The holes get clogged with carbon and the exhaust gas flow into the sensor chamber is restricted. So the response of the control loop is delayed by the sensor and the loop slows down. It's like having a logic chain in a control loop with one IC changing its propagation delay from 5nS to 500mS. (I thought i would NEVER use that analogy in an auto forum!)

So your recommendation is not to replace the ECT and thermostat?

How about ordering these parts below, are these the correct parts? I may just end up trying once more a brand new upstream O2 sensor

Is the correct thermostat for a 2004 I6 Chevy trailblazer part number 1511006 from rockauto?

Is the correct ECT sensor for a 2004 I6 Chevy trailblazer part number 213963 from rockauto?

Is the correct upstream O2 sensor for a 2004 I6 Chevy trailblazer part number 21054 from rockauto?
I bought an AC Delco from them and when the part came it was stamped NTK on the oxygen sensor.

Is the correct downstream O2 sensor for a 2004 I6 Chevy trailblazer part number 21044 from rockauto?
 

RayVoy

Member
Nov 20, 2011
939
BRomanJr said:
In my experience, the O2 sensor build quality, operating temperature and overall health affects the switching speed, the PCM only responds to changing signals from the O2 sensor and the PCM is clocked faster than the O2 can switch.
I believe, if you go back and re-read my post, you will find you are agreeing with me.

The sensor responds to mixture changes and passes voltage to the PCM when the mix ratio goes rich, reducing the voltage when the mix goes lean.

The PCM responds to the voltage by changing the bandwidth of the injector signal.

I believe I also said the scope picture shows that some sensors respond faster than others.

In the scope displays, there is a difference in reaction time; however, both sensors are new (one is not lazy), and probably, fully within spec. I think the PCM should be happy with either sensor installed.

mngopher22 said:
So your recommendation is not to replace the ECT and thermostat?
I'm not sure what others are recommending, and I am not offering a recommendation, however, the fuel delivery system is not very tolerant to engine temps that are below normal, even just a little below normal.
 

MAY03LT

Member
Nov 18, 2011
3,412
Delmarva
mngopher22 said:
Originally I went to autozone and got a bosch. Yes i know get ac delco. Then i bought AC delco one from rockauto, and that is what is currently in the vehicle.

Did you replace the upstream or downstream?
 

mngopher22

Original poster
Member
Aug 28, 2012
20
MAY03LT said:
Did you replace the upstream or downstream?
I have only replaced the upstream sensor.

I thought engine coolant should be around 210??? The needle on my car consistently reads two ticks to the left (IE I know its just the dash gauge thats why I read the engine data from OBD) but shouldn't it be at 210 exactly?

One person thinks the O2 senor data looks slow, and another thinks its ok, I am not sure which is correct. Does anyone know the bare minmum switch count expected to see before it throws a P1133? If I knew that i could easily calculate the frequency of expected O2 data.
I am extremely frustrated with this on going issue with my vehicle and I greatly appreciate the help and guidance.
 

MAY03LT

Member
Nov 18, 2011
3,412
Delmarva
mngopher22 said:
I have only replaced the upstream sensor.

The bottom line for the p1133/p0136 combo is that the pcm detects that the HO2S 2 (downstream) did not transition below 300mv and above 750mv during its "passive" test. This only applies if the LTFTs are in the single digits. I don't have the specifics on the parameters for getting the passive test to run outside of the engine has to be at operating temp. The 'informal' test would be to force a lean condition by doing a closed throttle decel in a lower gear and read the HO2S 2 voltage, and forcing a rich condition by accelerating to WOT and reading the HO2S 2 voltage. You might have to do it many times to catch it so be patient. Personally I do it with my scan tool over a scope because I want to see what the pcm sees. I do use a scope if I want to compare the sensors reading directly to the pcms reading.

mngopher22 said:
I thought engine coolant should be around 210??? The needle on my car consistently reads two ticks to the left (IE I know its just the dash gauge thats why I read the engine data from OBD) but shouldn't it be at 210 exactly?

After I did the thermostat in mine, the ECT read 206 degrees. Other members have reported ECT readings in the 199-201 range as "normal", regardless of what the gauge says.

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mngopher22 said:
One person thinks the O2 senor data looks slow, and another thinks its ok, I am not sure which is correct.

I can't tell by looking at the screens that you posted (which was awesome btw). My way for testing 02 response is unconventional and, well, is totally not safe. I wouldn't be able to sleep if I posted it publicly, but if you really want to know feel free to pm me.

mngopher22 said:
Does anyone know the bare minmum switch count expected to see before it throws a P1133? If I knew that i could easily calculate the frequency of expected O2 data.
I am extremely frustrated with this on going issue with my vehicle and I greatly appreciate the help and guidance.

I skimmed through the shop manual and I didn't see it referenced in the flow chart. For the time that you have in it now it might be best to bang in a downstream HO2S, reset the pcm, and compare the before/after O2 readings.
 

JerryIrons

Member
Dec 20, 2011
434
I just replaced my upstream sensor 3 weeks ago, bought it from rock auto. I have an I6 2006 EXT version. I bought an ac delco o2 sensor, from rock auto, and it was the exact same sensor that came with the vehicle, I could still read the part number on it, barely.

ACDELCO 2133539 Shipped is on my rock auto order.

If this helps at all

Before I ordered I checked part numbers on gmpartscenter or similar site.

-Jerry
 

mngopher22

Original poster
Member
Aug 28, 2012
20
JerryIrons said:
I just replaced my upstream sensor 3 weeks ago, bought it from rock auto. I have an I6 2006 EXT version. I bought an ac delco o2 sensor, from rock auto, and it was the exact same sensor that came with the vehicle, I could still read the part number on it, barely.

ACDELCO 2133539 Shipped is on my rock auto order.

If this helps at all

Before I ordered I checked part numbers on gmpartscenter or similar site.

-Jerry
Were you pulling any code before that? P1133 per chance?


After I did the thermostat in mine, the ECT read 206 degrees. Other members have reported ECT readings in the 199-201 range as "normal", regardless of what the gauge says.
I am consistently reading 190 or below so I should probably replace the Thermostat and ECT sensor, do you agree?
 

MAY03LT

Member
Nov 18, 2011
3,412
Delmarva
mngopher22 said:
I am consistently reading 190 or below so I should probably replace the Thermostat and ECT sensor, do you agree?

When mine crapped out (and threw a p0128) the ECT would only get to 181 degrees. The gauge was two ticks lift of center. It may be a matter of time before yours throws the p0128.

I'm not with the majority on the ECT sensor. I didn't do mine when I did the stat. I'd expect either an ECT sensor code or the temp gauge to be unstable when it fails. But, the majority has a good point about just doing it when doing the stat because it's right there. Your call boss.
 

mngopher22

Original poster
Member
Aug 28, 2012
20
I have a huge request from the community, could someone with a trailblazer and a OBD datalogger plot data of the upstream o2 sensor during idle and at 2000 rpm. I would like to compare with my o2 sensor data and determine if the o2 sensor data should have a higher frequency and also a 50% duty ratio
 

C-ya

Member
Aug 24, 2012
1,098
mngopher, what adapter and program are you using? I'd like to expand the PIDs I have available in Torque. I can't get the transmission temp to work correctly, for example. I am using one of the OBDII bluetooth adapters to connect to my HTC phone. It tracks most things well, but some things on this vehicle I'm not too sure about. Engine load, for example, intake air temp, and coolant temp are some that seem iffy. My coolant temp is generally around 195 (and of course the gauge shows 210!). This setup works great and with believable numbers in my wife's '04 Impala and in my '98 C1500.

Speaking of Torque (I have seen it mentioned here several times), is there a "section" for discussing it? Or maybe a PID depository? Searching for "torque" didn't give too many useable results, again most mentions just being in passing.
 

JerryIrons

Member
Dec 20, 2011
434
mngopher22 said:
Were you pulling any code before that? P1133 per chance?

No mine was a heater circuit code, I think P0135. If I get a chance I will try and record some data, but I am under the gun with a project at work right now.
 

mngopher22

Original poster
Member
Aug 28, 2012
20
Just adding more information about diagnosing my P1133, I have attached a picture of my gauge, it always runs at 2 notches below 210.
The second picture shows both upstream o2 sensors that i have. btw the AC Delco o2 sensor I bought from rockauto is labeled NTK on the sensor. strange
The third and fourth pictures show the connecter and the variable timing solenoid (camshaft position actuator solenoid). Its all flooded with oil, I have heard this is very common, I haven't thrown a code about it, so i havent replaced it yet, I just removed it and cleaned it all up.
 

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RayVoy

Member
Nov 20, 2011
939
mngopher22 said:
Just adding more information about diagnosing my P1133, I have attached a picture of my gauge, it always runs at 2 notches below 210.
Unless there is a stepper motor problem with the temp gauge, it should be at 12 o'clock.


mngopher22 said:
The second picture shows both upstream o2 sensors that i have. btw the AC Delco o2 sensor I bought from rockauto is labeled NTK on the sensor. strange
NTK makes ACDelco plugs and O2 sensors.

Perhaps, you'll find this link interesting: http://www.autoshop101.com/forms/h58.pdf

It is my opinion, that your new sensors are probably doing the job correctly, I would look for outside influence.

If the operating temp of engine is not impacting the reading, the readings could be contaminated by some other situation in the exhaust pipe; perhaps, something like an upstream exhaust leak. By any chance, do you have the infamous cracked exhaust manifold?
 

SAR85

Member
Jan 31, 2012
74
My gauge sits about two ticks left of 210 but I have confirmed that my temps are between 190 and 202 when warmed up, depending on acceleration, speed, etc. This is after replacing the thermostat. It seems others have reported the same thing, so maybe some gauges really do read and display the temp instead of a made up, calculated number.
 

mngopher22

Original poster
Member
Aug 28, 2012
20
RayVoy said:
Unless there is a stepper motor problem with the temp gauge, it should be at 12 o'clock.


NTK makes ACDelco plugs and O2 sensors.

Perhaps, you'll find this link interesting: http://www.autoshop101.com/forms/h58.pdf

It is my opinion, that your new sensors are probably doing the job correctly, I would look for outside influence.

If the operating temp of engine is not impacting the reading, the readings could be contaminated by some other situation in the exhaust pipe; perhaps, something like an upstream exhaust leak. By any chance, do you have the infamous cracked exhaust manifold?

In that pdf you link above, in section "Oxygen Sensor Signal Checks"
It states that you should run engine 2 mins at 2500 rpm, next line it states that signal frequency should be 8 cycles in 10 seconds ie at least .8Hz. Is this at idle then? or at 2500 rpm? Either way from my waveforms in the first post, The highest frequency I measure is 0.5 Hz which would be less than .8Hz thus P1133 insufficient switching.

My gauge sits about two ticks left of 210 but I have confirmed that my temps are between 190 and 202 when warmed up, depending on acceleration, speed, etc. This is after replacing the thermostat. It seems others have reported the same thing, so maybe some gauges really do read and display the temp instead of a made up, calculated number.

We will see if this fixes my temp. I have already ordered both thermostat and ect sensor.
 

RayVoy

Member
Nov 20, 2011
939
mngopher22 said:
In that pdf you link above, in section "Oxygen Sensor Signal Checks"
It states that you should run engine 2 mins at 2500 rpm, next line it states that signal frequency should be 8 cycles in 10 seconds ie at least .8Hz. Is this at idle then? or at 2500 rpm? Either way from my waveforms in the first post, The highest frequency I measure is 0.5 Hz which would be less than .8Hz thus P1133 insufficient switching.
.
I'm not disputing your readings, your new sensors are transitioning out of spec. What I'm saying, is (because they are new) the PCM should be happy with either sensor (even the Bosch), it's not, so there must be an outside (of the fuel delivery system) influence, impacting the exhaust gases.

We know water temp can impact the delivery, but yours is not that far off, I don't think we are going back and forth between closed and open loop. There is likely contamination of the exhaust gas.
 

mngopher22

Original poster
Member
Aug 28, 2012
20
RayVoy said:
I'm not disputing your readings, your new sensors are transitioning out of spec. What I'm saying, is (because they are new) the PCM should be happy with either sensor (even the Bosch), it's not, so there must be an outside (of the fuel delivery system) influence, impacting the exhaust gases.

We know water temp can impact the delivery, but yours is not that far off, I don't think we are going back and forth between closed and open loop. There is likely contamination of the exhaust gas.
I may just go ahead and order one more upstream sensor to rule it out.

Ok presuming the exhaust is getting contaminated, how would I go about looking for cracks on the manifold from underneath? The reason i ask underneath is because a couple months ago when all this started I pulled of the heat shield and visually inspected the exhaust manifold for cracks. I didn't see any cracks so I ruled out a cracked manifold. Now I will say I never got a real good look at the exhaust manifold from underneath because its very difficult to see. Any suggestions on getting a good thorough view of the manifold to assure that its not cracked?
 

RayVoy

Member
Nov 20, 2011
939
When mine cracked (I had an '05 Envoy before the Avalanche), the first sign was a little exhaust noise when starting cold that went away as the manifold got hot.

I was able to see it using a small makeup mirror from above. The cracks were dark against the red brown of the iron.

I drove it cracked for a little while, maybe a month, before I fixed it, but it did not cause the CEL to light. Others have reported the CEL lighting and I believe it was an O2 code (don't recall which one). I suspect, mine was sealing the leak before the PCM went into closed loop.

I would say, if yours runs quietly, there is probably no manifold leak.
 

mngopher22

Original poster
Member
Aug 28, 2012
20
UPDATE
The GOOD
ok i replaced the thermostat and ECT. The ECT sensor broke off in the block and I had to use a reverse thread drill bit to back it out. Glad I am done with that. On a positive note, the thermostat and ECT change made my temp gauge read 210 dead on when im driving so I am very happy about that.

THE BAD
I am still having issues though with P1133 etc. I ordered a brand new oxygen sensor for the upstream from rock auto. It can today,I installed it and took some readings. On the first engine start with the new o2 sensor the readings are picture PERFECT!!! I was SOOO HAPPPYYY. I took 3 Readings at IDLE, 2000 rpm and 2500rpm. I have posted below the first 3 readings at specified engine rpm's. At idle you can see nice 50% duty cycle between rich and lean, also the freq is at .33Hz. At 2000rpm the freq is .73Hz and at 2500rpm the freq is 1.2Hz. All looks good.
Fast forward 2-3 minutes, I turned the engine off and on again to check and make sure all is still good.
I took the three readings again at idle, 2000rpm, and 2500rpm. The next three pictures show the readings. At idle I lost my nice 50% duty cycle and the frequency is much slower at 0.2Hz. At 2000rpm engine is runnning rich most of time and frequency of o2 sensor is 0.4Hz. At 2500rpm the frequency is 0.58Hz. What happened to my o2 sensor? Its brand new, it worked for about 2-3 mintues and now its slow again.
I would appreciate any advice as I am really close to just sucking up my pride and taking it to the stealership.

I also attached picture of the brand new sensor I put in this morning.
 

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JerryIrons

Member
Dec 20, 2011
434
Are by chance losing coolant? I worked on a friends care once that was burning coolant, which would cause the 02 sensor to go bad very quickly. But not within 2 or 3 minutes. (leaky head gasket) Is the wiring to the o2 sensor worn or rubbing against something? Plus the engine has to be completely warm before the o2 sensor kicks in fully, but I'm sure you know that. How about something easy like air filter being plugged up. Are you burning oil? Just shots in the dark.
 

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