Dummy check gauges light on and engine temperature gauge stopped working

am-radio

Original poster
Member
Apr 24, 2012
178
The dummy check engine light came on today while my wife was driving. The engine temperature gauge never left cold. She drove where she was going and shut it off. It sat for 3 or 4 hours. She started it again and went to her sisters. She called me when she got there. She said it wouldn't start. She said it sounded like it was trying to start after it was sorta running, (but not grinding). I drove in and checked fluids to be safe. All fluid levels were normal and not mixing. I tried starting it and it didn't start right away. I tried a second time and had to give it gas to get it to start. It started and of course smelt of rich fuel. It seemed to run ok. I got my wife to drive it home, (20 minutes). The factory engine temperature gauge never moved off of cold. I do have a scangauge installed and the temperature stayed around 190 F, plus or minus a few degrees. It did climb to 198 F sitting in traffic, and dropped back to 190 F when driving. The truck is now parked. I know GM has issues with electrical and their instrument clusters. Do I need a new temperature gauge, sensor, sending unit, or is there something much more major? Also, why would the truck not want to start? Does it go into a safe mode or something when it senses that the engine is not at temperature?

Please note that I have the Denali with the 5.3 liter V8, and not the 4.2, 6 cylinder.
 

CaptainXL

Member
Dec 4, 2011
2,445
I know that bad batteries can cause weird thing to happen. Do you still have the original battery? If unsure check the date code on it.
 

am-radio

Original poster
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Apr 24, 2012
178
Its still a gm battery but has a full charge. Never had starting issues or electronics not working.
 

CaptainXL

Member
Dec 4, 2011
2,445
am-radio said:
Its still a gm battery but has a full charge. Never had starting issues or electronics not working.

You said in your original post... "why won't the truck start?" It's time for a new battery.
 

am-radio

Original poster
Member
Apr 24, 2012
178
It was cranking fast and was always fully charged every time I checked it. I will go out and check the voltage. It's a possibility. Seemed more like a fuel/air off ratio, then a cranking issue.
 

am-radio

Original poster
Member
Apr 24, 2012
178
Just went outside and checked the battery voltage. Truck has been sitting for 4 hours in temperatures just below freezing. Voltage was 12.57 which is pretty much a fully charged battery.
 

CaptainXL

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Dec 4, 2011
2,445
How many miles and what has been services as far as scheduled maintenance thusfar? Also, any history of major work being done on vehicle or accidents?
 

am-radio

Original poster
Member
Apr 24, 2012
178
I have about 148,000 km on the truck. No accidents that I know of. Regular oil changes. Front and rear riffs, transfer case and tranny around 110,000 to 120,000 km. I bought it second hand with 130,000 km. History showed clean when I bought it. Can't see any signs of body work or damage.
 

am-radio

Original poster
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Apr 24, 2012
178
Water pump changed and tensioner pulleys, idler pulley and belts changed this summer.
 

CaptainXL

Member
Dec 4, 2011
2,445
am-radio said:
I have about 148,000 km on the truck. No accidents that I know of. Regular oil changes. Front and rear riffs, transfer case and tranny around 110,000 to 120,000 km. I bought it second hand with 130,000 km. History showed clean when I bought it. Can't see any signs of body work or damage.

So you bought it with 130,000 km on it. How do you know that it has had regular oil changes or transfer case fluid changed or any other scheduled maintenance prior to that? Are you taking someones word for it?

When you said the water pump was changed, was the thermostat changed as well?
 

am-radio

Original poster
Member
Apr 24, 2012
178
Receipts. Not sure about the thermostat, but I believe on the 5.3 if you change the water pump the thermostat has to come out.
 

CaptainXL

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Dec 4, 2011
2,445
am-radio said:
Receipts. Not sure about the thermostat, but I believe on the 5.3 if you change the water pump the thermostat has to come out.

It would be on the reciept if the thermostat was changed.

The first thing to do is to retrieve the codes since the CEL is on.
 

Blckshdw

Moderator
Nov 20, 2011
10,657
Tampa Bay Area, FL
:undecided: How did it run while driving, and idling? Was it rough or choppy? Flashing CEL, or was it solid? Smelling of rich fuel makes me wonder about your spark plug situation, since you didn't mention those being changed at all.
 

am-radio

Original poster
Member
Apr 24, 2012
178
It ran fine once started. It's not really the cel. It's a light that tells you to check your oil pressure gauge and engine temperature gauge. I'm going to try to pull codes and see what I get.

Does the truck go into a safe mode when it thinks the engine temperature is not at operating temp?

Don't think the plugs have been changed. Was on the to do list this winter.

Can I damage anything by running the truck with the engine temperature gauge not working?
 

The_Roadie

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Nov 19, 2011
9,957
Portland, OR
I'm surprised nobody mentioned an obvious item: If the scangauge has good readings for ECT, the sensor and PCM and the data stream are OK. The PCM reads the sensor and reports the temperature to any module that asks for the data. I think this issue is contained to the gauge cluster, maybe just a bad stepper motor, but it is odd. I would leave the scangauge in there and make sure the driver always consults it.

The service manual says the Check Gauges light goes on if the gauge cluster gets a data message from the PCM that the coolant temp is over 257F/125C. Or the oil pressure is low. Or if the gauge cluster hasn't been programmed after replacement. From that short description, I don't see how the cluster would know if the gauge needle isn't moving as it should.

Any chance the oil pressure switch is bad and the pressure gauge was also at zero?

If the REP lamp was dark, it probably wasn't in safe mode, and that's typically reserved for issues with the accel pedal position or throttle body sensors (and the cross-connection to the fan clutch reference voltage). GM designers were sometimes goofy, but I don't see them disabling a vehicle in case the ECT sensor or one wire fails.

As you said, check stored codes and schedule new plugs.
 

am-radio

Original poster
Member
Apr 24, 2012
178
What is the REP light?
The engine oil pressure gauge stayed in the mid range the entire time. My Scangauge is hooked up permanently. I am going to change one of the read outs to show oil pressure.
I'm going to go try to pull codes once the sun comes out. Will be soon.
I found a local guy that will change all 6 stepper motors for $200 if I remove the cluster.
 

The_Roadie

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Nov 19, 2011
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Portland, OR
am-radio said:
What is the REP light?
Hover your cursor over the term (especially if it's underlined. View attachment 25372
I found a local guy that will change all 6 stepper motors for $200 if I remove the cluster.
I wouldn't use that guy. You can buy the steppers for $30-40 on Ebay, and it's under an hour's worth of soldering and there are Ebay vendors that do it for $50-125. I'd negotiate with that guy and get a fair price. $200 is only a good price if the alternative is the dealer. :eek: :eek: :eek: :crazy:
 

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am-radio

Original poster
Member
Apr 24, 2012
178
I just tried pulling the codes with an OBD II code reader.

P0116 Generic engine temperature circuit range/performance

I also checked the battery voltage, the truck has been sitting for 16 hours outside (-10 C or 14 F) and now shows 12.17, down from 12.57, last night. Could be because the headlights come on when you unlock the doors?? Or a weakening battery.
 

CaptainXL

Member
Dec 4, 2011
2,445
For the P0116 looks like you need a new thermostat and coolant temp sensor. Also your battery needs replacing. Not at all uncommon for this old a vehicle.
 

am-radio

Original poster
Member
Apr 24, 2012
178
Why would my scangauge be working and showing a steady 190F temperature, once up to temperature?
 

CaptainXL

Member
Dec 4, 2011
2,445
am-radio said:
Why would my scangauge be working and showing a steady 190F temperature, once up to temperature?
;

Well for one 190 is borderline too low of a temp. Second the tstat could be slow to open/close which is more likely. But since you need to replace the thermostat you should change the coolant temp sensor as well since it could be the problem as well. The sensor could have an internal problem that shows itself on a rare occasion.

The P0116 means there is a cooling circuit problem. You can check the wiring coming off the coolant temp sensor and test the resistance of the temp sensor if you want. But in my experience you need the tstat and sensor anyway being you have a 6 year old truck. Its your choice. Tshoot or replace parts.
 

am-radio

Original poster
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Apr 24, 2012
178
I'm going to buy a new ECT from GM this morning. I'll change that first then see if I can find a write up for changing the thermostat on a 5.3L V8.
 

The_Roadie

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Nov 19, 2011
9,957
Portland, OR
am-radio said:
Why would my scangauge be working and showing a steady 190F temperature, once up to temperature?
I don't see anything wrong with 190. The PCM tells the gauge to display straight up 210 for most ACTUAL temperatures from 185-220, so as not to give Ma and Pa Kettle (the typical non-enthusiast owners) any cause for alarm.

But as has been pointed out, it may be opening too much, too soon, and delaying the initial heat-up. The PCM has tables that vary the expected time delay according to outside temp and how hard you're driving it. Maybe keep a log of scangauge temp versus time and outside temp on the next werm-up cycle. And any of us with scangauges or smartphones with Torque can do the same.
 

CaptainXL

Member
Dec 4, 2011
2,445
am-radio said:
I'm going to buy a new ECT from GM this morning. I'll change that first then see if I can find a write up for changing the thermostat on a 5.3L V8.

Just had another thought.

When you see 190 on the scangauge does the engine start and run OK? Is it safe to say that the starting and rich running issues are intermittent in nature?
 

CaptainXL

Member
Dec 4, 2011
2,445
the roadie said:
I don't see anything wrong with 190. The PCM tells the gauge to display straight up 210 for most ACTUAL temperatures from 185-220, so as not to give Ma and Pa Kettle (the typical non-enthusiast owners) any cause for alarm.

I'm kind of forced to agree will Bill. But its kind of a gray area we are getting into without knowing the coolant temp scan tool parameters which can be found in the service manual. The PCM expects to see a certain temp by a certain amount of elapsed engine run time. If not the pcm will set a P0128. But that's not the code you have. So I digress.
 

am-radio

Original poster
Member
Apr 24, 2012
178
The 190 F is with the scangauge. The factory temperature gauge usually shows 100 C or 212 F.
I started it this morning. It started no problem, and no lights came on, and the factory temperature gauge is working now.
Data, from a cold start:
Scangauge temp Engine temperature gauge Outside temperature 0 C or 32 F (time increments every 30 seconds)
31
33
42
55
64
75
83
91
98
105
112
119 50 C
125 55
132
137 62
143 65
148 70
154 72
159 75
163 77
168 80
173 85
177 90
181 95
184 Engine RPM drops from 800 to 600
188 100
188 100
190 100
190 101
190 100
190 99 99-101 Celsius is normal operating temperature for the Envoy factory gauge.

Now i'm confused. It started bad twice yesterday for the wife, when it was hot. Wait and see now. I did not change anything.
 

CaptainXL

Member
Dec 4, 2011
2,445
Monitor the coolant temp with the engine hot and the key on and engine off. You might catch the coolant temp dip way low which would cause a rich condition and hard starting. This would indicate a faulty sensor or open in the circuit. Disconnect the sensor and see if you get the same symptoms. Something else that would further complicate the starting of the engine is if the plugs became fouled from trying to start with too much fuel.
 

am-radio

Original poster
Member
Apr 24, 2012
178
Just to clarify for myself, but the only way the temperature would drop suddenly with the truck off would be if the ECT is faulty or shorting out? It should gradually drop with the truck shut off, no?
 

CaptainXL

Member
Dec 4, 2011
2,445
am-radio said:
Just to clarify for myself, but the only way the temperature would drop suddenly with the truck off would be if the ECT is faulty or shorting out? It should gradually drop with the truck shut off, no?

Correct. You might see a spike in temp after turning the engine off because the water pump isn't circulating coolant. But after that it should start tapering off.
 

am-radio

Original poster
Member
Apr 24, 2012
178
I'll check tomorrow when I get a chance. I'll have to rely on the stock gauge as the scangauge only works when the truck is running. It's sitting in the garage now.
 

CaptainXL

Member
Dec 4, 2011
2,445
am-radio said:
I'll check tomorrow when I get a chance. I'll have to rely on the stock gauge as the scangauge only works when the truck is running. It's sitting in the garage now.

You can't go by the gauge on the dash. Most scan tools work with at least the key on. I would double check.
 

am-radio

Original poster
Member
Apr 24, 2012
178
My OBD II will work, but not sure if shows live data. Tossing a few things in my head. If the stepper motor fails, will it start working again? Is this true for the ECT also? I can't figure out why it just magically starting working again, without doing anything to fix it.
 

Chickenhawk

Member
Dec 6, 2011
775
I have to agree with the speculation about Coolant Temp Sensor (or maybe thermostat.)

When I first read your post, the first thing that came to mind was that the Coolant Temp Sensor wasn't working properly. If it indicated to the PCM that the engine was very cold but it was actually warm, it would be very hard to start and once running, would run very rich for a while. I think your scanguage just wasn't being monitored at the time the Coolant Temp Sensor got stuck at full cold.

Of course, the thermostat could also be sticking and that would cause similar symptoms, but sticky thermostats are usually longer-term problems than spikey temperature fluctuations.

If it was me, I would change the temp sensor AND the thermostat anyway. (190 is still a bit cold. It should read 198 to 205 when normal.)

Also, get your battery load-tested. It may voltage test okay but when they old, they drop quickly under load. If the battery is original you are about due.
 

Burn Down

Member
Dec 14, 2012
2
Hi all,
I was online looking for some info on this very problem. I have had this happen for 4 years now. I own a 2006 Trailblazer SS. The problem is not the ECT sensor or anything else. It has to do with plugging the vehicle in at any temperature above 0*. If you do, the little dummy gauge light can comes on not the cel & only the engine coolant gauge will stop working. The engine can be hard to start sometimes & or start and run like normal. If the engine is hard to start and won't stay idling, put the accelerator pedal to the floor while cranking, once started, use just enough throttle to keep the engine running, after a moment or two it will run like normal. GM is aware of this and has a reroute of some wiring or the block heater cord??? I don't remember what it was. I just made sure to not plug it in when temps are above 0*. Well tonight my daughter was driving it and she had plugged it in while it was above 0* and it left her stranded at the store. Im now pissed at this thing and will fix it. Gm wanted to charge me to do the update and being a Diesel Technician for Caterpillar I said no way I'll do it myself, just has taken me awhile :biggrin:... Well now I'm motivated. Ps GM has a small scan tool that resets this error, I had the dealer do it a couple of times for me. I will post back with the re-route procedure and what it entails as soon as I can get it.
Albert
 

am-radio

Original poster
Member
Apr 24, 2012
178
That's an interesting response. I don't really understand how that would effect it, but the day I did have the problem, the block heater was plugged in. If it gets below -15 Celsius I plug in. I'm interested in hearing more about this.

I changed my battery and did nothing else and the problem hasn't come back yet.
 

Burn Down

Member
Dec 14, 2012
2
It has something to do with one of the sensors being cold and the water temp sensor being to warm (from the block heater). The Ecm thinks there is a issue with the ECT sensor because of the temp. difference. When the engine doesn't know what the water temp. is it doesn't have the proper fuel map for starting cold, hence the hard start. Anywho, give me a week or so to see if I can get my hands on this update or talk with some Techs at the dealer that have done this job. I will post up the info for you, as I need to do it on my TBSS as well.
 

am-radio

Original poster
Member
Apr 24, 2012
178
I'll sit and wait for your response. Hasn't been cold enough lately to warrant plugging in the envoy, to see if it happens again.
 

am-radio

Original poster
Member
Apr 24, 2012
178
Well I've done nothing since posting here. The dummy light to check gauges and the engine temperature gauge came on once more. The truck block heater was plugged in. Both times it happened the block heater was plugged in. Apparently this is a common issues with some GMC's. Anyone else heard of this?

Here is another forum post on the issue.

My Trailblazer Fun - Fbody Generations
 

am-radio

Original poster
Member
Apr 24, 2012
178
Reviving my own thread. The truck is running like crap again. I think it has to do with plugging in the truck when it's not very cold outside. I plugged in the truck last night and the weather temperature warmed up to -7 C or 20 F. Truck started fine but now is running rough and has the same dummy lights on. Won't accelerate very well. I hope the wife can make it to her destination this morning.
 

bobdec

Member
Apr 19, 2013
233
This cut/paste from GM mode 6 diagnostics helps understand how the P0116 is set on your engine. Basically comparing ETC (coolant temp) to IAT (input air temp). Interesting is how the Block Heater detection formula works. I see other hits searching 'DTC P0116 and block heater'. Some mention dash temp gauge not working. Even some software TSB's out there. Are you still getting the P0116 ??

View attachment 31570
 

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