Reduced engine power light

guy77

Original poster
Member
Dec 4, 2011
8
Started my SUV to leave for work this morning at -11C ( 12 F). The Beast started fine.
I should mention it has 293,000km ( 182,000miles). Everything original except.... thermostat , fuel filter, air filter and plugs and changed a iso-converter valve in the transmission valve body 4 days ago.(Transgo kit) Its a 2003 trailblazer.

I pushed the gas and my top speed was 40km/hr and the engine service and Reduced engine power light came on!!

Took it to my bros shop and we got codes .......
1221 ( throttle position sensor)
1635 ( 5 volt circuit)

I have seen other posts about 1221 code coming up but none that have 1221 with 1635 and so that is why I posted.

I left the truck turned off for 3 hours and when i started it up again it ran fine !! Its midnight now and have driven another 50 km with no troubles.
I will start by cleaning the throttle body in the morning. I will keep everyone posted of my progress.
 

CaptainXL

Member
Dec 4, 2011
2,445
Your fan clutch wiring is frayed/open or shorting to ground. Replace or repair harness going to fan clutch. The fan clutch used the same 5 volt reference circuit as the APP sensor for throttle control.
 

guy77

Original poster
Member
Dec 4, 2011
8
Interesting. I have heard a lot of people have issues with the fan clutch.

So your saying the throttle position sensor is most likely not damaged but fan clutch wiring is?


Thank you.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
The 5V reference circuit is SHARED by the accel pedal sensors (2), the throttle body butterfly valve position sensors (2), and the fan clutch RPM sensor. Any problem in wiring or a sensor could croak the 5V precision voltage reference and cause a REP event. Very often, mechanics don't know about the interaction, and they blindly swap pedal sensors or throttle bodies and never look at a wiring diagram and guess the fan clutch could be involved.
 

LikeEnvoy

Member
Apr 17, 2012
128
Winnipeg, MB
Is this related?
My 2007 envoy started very roughly tonight at work- -27c. The traction control light , check engine light and reduced power light were all on steadily.
The idler pulley also whined for a few minutes. I tried revving to see if the roughness would smooth out but it just stuttered and
almost stalled when the revs came down again. I left it to warm up.
When I came back it was still lumpy- felt like a bronco bucking when I sat inside.
Tried restarting- no change. tried again- no change.

Tried driving (had to, because I work in the middle of nowhere and this temperature can kill)

Once clear of the gravel roads I tried speeding up on the highway but it wouldn't go more than 30mph/50kph.
Police pulled me over for going slowly! He accepted my explanation when he saw the lights though.
Limped home and every time i stopped at lights it felt like a bronco again.
But now what?
Left it in the garage while I had supper. Now started it and it runs smoothly! (only -24c now) Only the check engine light is still on (traction control and reduced power lights off)

1. Why were all three lights on? Why suddenly tonight in the cold?
2. why wouldn't it clear when I tried restarting a few times?
3. Why is it running smoothly now and only the check engine light on?

If I drive to work tomorrow will it repeat the problem, I wonder?

Sound familar to anyone?
 

guy77

Original poster
Member
Dec 4, 2011
8
Thank you Roadie and CaptainXL. Interesting that the 5V reference circuit is shared by all 3 items ( pedal, throttle body and fan clutch).
So far the problem has gone away.

And yes your right most mechanics don't know that the fan clutch uses that same 5 volt circuit!
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
guy77 said:
And yes your right most mechanics don't know that the fan clutch uses that same 5 volt circuit!
And they dismiss any customer bold enough to Google on the net and bring suggestions into them. Some dealers especially HATE to be informed about relevant recalls or TSBs because, as they have been trained, the customer is always WRONG.
 

LikeEnvoy

Member
Apr 17, 2012
128
Winnipeg, MB
guy77, when you said "So far the problem has gone away ",
did you find a specific fault in your wiring for the 5v supply?
(Or has the problem just not occurred again after you cleaned the throttle body??)

If you did find a specific place/connector to check that would be useful.

My Envoy started ok this morning with only the check engine light on; and after a short trip then restart, the check engine light cleared too!
I can't get into work today to borrow my colleague's code checker so that will be tomorrow.
I could only see the connector on the left side of the fan housing, near the battery, driver's side and it didn't seem damaged. I tried removing this and reseating iteither.
Obviously the fan clutch wiring must be on the engine side of the fan but I don't know where else to look.

I'll report if I find something new, and especially when I get the code check done.
(Although I fear the codes may have cleared if the check engine light has gone off now :crazy: )

You can tell I really don't want to take it to a dealer, can't you; not surprising with the results Roadie and you were describing.
 

NinjuhhNutz

Member
Oct 15, 2012
720
the roadie said:
And they dismiss any customer bold enough to Google on the net and bring suggestions into them. Some dealers especially HATE to be informed about relevant recalls or TSBs because, as they have been trained, the customer is always WRONG.

When I went to ask about the price for diag. and replacement of the fan clutch or harness (whichever it turns out to be) the guys at the stealership gave me this *who the &%$# do you think you are?* look when I explained to them the reason I was bringing it to the dealership it that I don't have the equipment to 110% pinpoint the issue and that if they told me it was the fan clutch, then I go out and buy one and replace it myself, it turns out NOT to be the issue, I'm stuck with a non-functioning truck and still out the $ for the fan clutch. He could tell I wasn't there to make friends, as I had already been given the run-around for asking for the price of diag/replacement/labor for 2 specific parts that I obviously "can't know is the issue" without proper diagnostics done by a GM Dealer :hissyfit:

if I knew with complete certainty that it was this or that, I would replace it myself and steer clear of that place :/
 

guy77

Original poster
Member
Dec 4, 2011
8
Hi LikeEnvoy... In regards to your question :

"guy77, when you said "So far the problem has gone away ",
did you find a specific fault in your wiring for the 5v supply?
(Or has the problem just not occurred again after you cleaned the throttle body??)

It turns out the problem has just not occured any more. It has gone away by itself.


I did inspect inside the throttle body 2 nights ago and there was an 1/8 in of gunk inside. I cleaned it out.
 

moneypit

Member
Dec 7, 2011
214
hey guy, could you elaborate on the "iso-converter valve in the transmission valve body with a transgo kit" replacement, why? Thanks ps I once got that reduced power light after a p/s hose repair and I disconnected and reconnected the 3 big connectors upper left of engine and it went away? not sure if it was even relevant or a fluke?
 

LikeEnvoy

Member
Apr 17, 2012
128
Winnipeg, MB
Problem Solved(??)

I think my Envoy is working fine now although can never be 100% sure.
What did I change??... The battery!
Sorry no codes to compare- I never got to work when my colleague was there with his checker.

It did it again on Thursday morning- started ok but 30 seconds later, as I was unplugging the block heater cord, the
revs died off as if the engine had stopped- then it picked up again but began idling roughly- lumpy as before.
I checked the dash and sure enough- Stabilitrak warning/check engine/reduced engine power lights.

I thought about it and realised that when I turn the key at very low temperatures like these, everything goes silent for half a second
and no lights are on the dash; then it suddenly kicks the engine into life.

I seem to remember now that when its warmer it turns the engine over immediately- no delay.

So I had an idea- if the battery was weak and when I connected the starter the voltage was dropping too much- maybe the engine computer was resetting;
losing its memory. It would then begin running its default settings and those are probably based on 15°c (standard temperarature for many systems).
So in -29°c it would likely say- what the heck, it's rather cold! and it would dump lots of fuel in to richen the mixture- instant rev drop and lumpy /rough running!
It would then find the engine performance was awful and emssions were awful so it would trigger all the check engine and reduced power states.
Maybe also the Stabilitrak start-up check relies on a voltage (maybe that 5v supply you talked about) to do its sanity checks.
Therefore starting with this voltage missing or out of limits would trigger that warning too.

It all made sense so I put a new battery in.
The first start showed immediate turn over- no delay; much faster turn-over speed too.
Also... the check engine lamp now stays on while cranking; with the old battery it had always gone out when the key was turned and all went silent.

So far all is good- it has been starting fine even in cold temperatures and the engine light stays on as I crank; turns off when engine is running.


So some clues were there but I did not see them because it had been deteriorating over a long time and I got used to it going silent for half a second when
turning the key in very cold weather; I just thought it was natural for cold weather to affect everything. I think many of us get caught thinking that if it still
starts the engine then it must be OK!

FINDINGS
Assuming my theory is correct and a bad battery was dropping voltage and resetting the computer, I think the designers could have designed the engine computer
to hold some reserve power by capacitance, to prevent voltage drop to the computer when the starter engages. It could make cars that much more reliable.

I hope this gives a few more people in cold climates the idea to check their battery and change it if the same thing happens.
$113 is not too much to pay these days compared to some parts.

CD



before it wnet h
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
LikeEnvoy said:
So I had an idea- if the battery was weak and when I connected the starter the voltage was dropping too much- maybe the engine computer was resetting;
losing its memory.
I agree 100% with this analysis.
...I think the designers could have designed the engine computer
to hold some reserve power by capacitance, to prevent voltage drop to the computer when the starter engages. It could make cars that much more reliable.
Not really. It would enable folks with bad batteries to get farther from home before 100% death and then they're stuck. Better that the bad battery get diagnosed and force the owner to replace it. I'm not a fan of coddling marginal parts along.
 

Denis7966

Member
Dec 22, 2011
45
LikeEnvoy said:
Is this related?
...The traction control light , check engine light and reduced power light were all on steadily.
...I tried revving to see if the roughness would smooth out but it just stuttered and
almost stalled when the revs came down again.

Sound familar to anyone?

Sounds VERY familiar to me.
Same thing happened to me last week (during the deep freeze). What surprised me was that the morning it happened, we were on our way out of the deep freeze. I had no problems starting at -29c (-20F) and -27c (-17F) the two previous days, but when it came to a pitiful -22c (-8F), the same thing you described happened to me; traction control light, check engine light and reduced power light all came on, and stayed on; and like you, it felt like a bucking bronco, and trying to rev the engine only brought it up to about 900 RPM.
I waited a bit, but when it didn't seem to get any better, I turned off the engine, waited about a minute, crossed my fingers and tried again. This time everything was normal - like nothing ever happened - except that the CEL was on. I drove to work without a problem; however, when I got out of work and turned the key, the same thing happened - unlike yourself, when I turned it off, then back on, everything was fine again.
When I got home, got my scan tool and pulled the code - "P2176 Throttle Position Sensor Minimum Position Not Detected".
Since its warmed up, everything has been great - guess they just don't like the cold.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Denis7966 said:
When I got home, got my scan tool and pulled the code - "P2176 Throttle Position Sensor Minimum Position Not Detected".
Since its warmed up, everything has been great - guess they just don't like the cold.
When was the last time you cleaned the back of the throttle body? Sticky gunk can freeze the plate in position and cause intermittent REP behavior.
 

Denis7966

Member
Dec 22, 2011
45
the roadie said:
When was the last time you cleaned the back of the throttle body? Sticky gunk can freeze the plate in position and cause intermittent REP behavior.

Never have cleaned it (30k miles), but it did cross my mind (after seeing the P2176 code) that I should probably get to it this spring when the weather gets warmer.
It looked clean last spring when I looked at it, but its true that I can't see the back of it - just figured that if the front looked cleaned, the back should be good - guess I was wrong.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Denis7966 said:
...its true that I can't see the back of it - just figured that if the front looked cleaned, the back should be good - guess I was wrong.
Hehe. That's funny. :rotfl:

The front can be clean, but the back can look like the bottom of muck boots used for ten years worth of cleaning the elephant stables after circus shows, never ONCE having been hosed off, and then baked in an oven at 275 degrees for three months, and then dragged through ten campfire pits worth of ash, then dipped in hot tar in a roofer's apparatus, then dipped one last time in French Roast coffee grounds found in the dumpster of a coffee shop that went bankrupt after having been found to poison and kill seven of its patrons in 2004.

That's icky. :biggrin:
 

guy77

Original poster
Member
Dec 4, 2011
8
Hi MoneyPit
In replay to your question "iso-converter valve in the transmission valve body with a transgo kit" replacement,why?"


My torque converter was not locking up properly on the highway it would slip out a bit and come back in between 80km and 100km/h but then it would stay locked after 110 km/h. This caused my rpm to jump higher every time it slipped and also caused mt to burn more fuel!

I read about installing the ISO-Converter regulator valve from the Transgo SK 4L60e shift kit.
I did not install the whole kit only the one valve body for torque converter lock up.

Just to let everyone know you need to actually drop the valve body to change out the old ISO-Converter regulator valve. The clip to pop out the old part is not accessible from the bottom of the valve body its accessible only from the top. So you have to drop the valve body to access it and make sure you don't drop the check balls!
 

LikeEnvoy

Member
Apr 17, 2012
128
Winnipeg, MB
Denis7966 said:
Sounds VERY familiar to me.
Same thing happened to me last week (during the deep freeze). What surprised me was that the morning it happened, we were on our way out of the deep freeze. I had no problems starting at -29c (-20F) and -27c (-17F) the two previous days, but when it came to a pitiful -22c (-8F), the same thing you described happened to me; traction control light, check engine light and reduced power light all came on, and stayed on; and like you, it felt like a bucking bronco, and trying to rev the engine only brought it up to about 900 RPM.
I waited a bit, but when it didn't seem to get any better, I turned off the engine, waited about a minute, crossed my fingers and tried again. This time everything was normal - like nothing ever happened - except that the CEL was on. I drove to work without a problem; however, when I got out of work and turned the key, the same thing happened - unlike yourself, when I turned it off, then back on, everything was fine again.
When I got home, got my scan tool and pulled the code - "P2176 Throttle Position Sensor Minimum Position Not Detected".
Since its warmed up, everything has been great - guess they just don't like the cold.

Hi Denis7966 and others,
I posted almost a year ago about my 2007 Envoy with all three lights and a slow crawl home and I thought I had fixed it with a new battery. Seemed like my diagnosis made sense- even Roadie thought so.

Guess what? It just did it again; at work -34C, this time it had been left only from 7am to 1pm. I left it running for 30 mins to warm up but it still was rough and several restarts did not change it.
I got home slowly, tried a restart again- no good, so left it. 1 hr later it started fine!
THIS TIME though, my brother in law came over with his scan tool. It pulled code 2176 just like yours, Denis.
I cleaned my Throttle body last summer but maybe its dirty again?

I don't know if this code is because:
a) the throttle butterfly does not shut properly so the sensor doesn't detect minimum
or b) the wiring to the Throttle body is faulty (intermittent) and so does not give the right signal when you start up.

Clearly the cold affects the problem.
So unless anyone has definitely located the problem and can point me exactly to the culprit, I will hope this keeps working in the meantime and wait for some warmer weather and pull the connector apart.

Happy New year to all!

CD
 

LikeEnvoy

Member
Apr 17, 2012
128
Winnipeg, MB
Today it did it again about 3 seconds after starting (only about -23C today).
I had the checker with me this time and connected it after turning off.
This time I got codes 1516, 2101 (and repeated again so 4 code entries in the list).

Started again and ran normally although with Service Engine light on.
Don't understand why it can run ok one time and not the next.


Just searched for several hours and finally got the right search terms- found this item in the old trailvoy site:
http://forums.trailvoy.com/showthread.php?t=81625

That was 2010 and the thread never had a final solution so I still don't know the excat place to look although it sounds like either the
throttle body connector or the throttle body itself may be the culprit.


It also seems though that the throttle body could be sticking ( dirty or maybe ice sticking the butterfly valve). i.e unless someone knows definitely the exact place to look the nit s still up in the air. Damn annoying; and in this temperature I don't want to be working on the car (and don't want to break anything either).

Can't see how to remove the throttle body plug- these clips on the new cars are dastardly- you need a degree just to know how to remove a plug.
The small sensor next to the throttle body plug came out ok - a simple lift up clip- that looked nice and clean. That was enough for this evening too dark now and too cold.

Common pattern seems to be = start ok in garage in morning; drive somewhere and leave it outside for a while - starts and throws the lights and reduced power and rough idle.
Still don't understand why the stablitrak light came on yesterday (and last year); what's the connection? That thread from 2010 also menti9oned the stabilitrak light.


Starts ok at the moment and I cleared the SES light so will try tomorrow (have to go to work again) and just hope it runs ok later tomorrow when I am out of town again at work.

CD
 

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