Automotive Question

DRC Archive Lounge Lizard
1

I have a 2003 GMC envoy. When I was driving on I95 (60 mph) last evening and was about to pass the construction site and had a semi sweet mechanical smell waft through the cab. It was only for about 2 seconds then it was gone. Immediatly sfter this smell disapeared the check engine light came on with the code P0128. While I drove home I paid special attention to the oil telp and oil pressure. The temp ran normal but the pressure gauge seemed a little higher then normal (approx 45-50). When I stopped at a light the pressure gauge lowered back to 40. When I accelerated off the light the pressure gauge rose to 50 (gauge range is 20 - 80). This may be me being overly sensitive to the gauges but I do not remember the pressure gauge having this much movement.
When I got home I ran the code P0128 OBDII DTC code is defined as Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature).
From reading I got this:
“This can be caused by Low engine coolant level Leaking or stuck open thermostat Faulty cooling fan (running too much) Faulty coolant temperature (ECT) sensor Faulty intake air temperature (IAT) sensor”
I checked the coolent level this morning and it is to the top of the radiator and the reservoir was just less then the max coolant Level. The tstat is the next lest expensive item but I would have to drain the antifreexze.

What really perplexes me is the smell right before the light came on. This would lead me to beleive that I have a leak or a seal issue where coolant went through gasket. The pressure gauge movement also raises questions.

Any info would be appreciated

2

Had one of techs over my shoulder reading your post, (GM dealer)

He said mainly thermostat for this consern, still could have a leak with a air pocket in the engine so level would still be full untill the air pocket pops.

Heres alldata definition and trouble chart for your code.

CIRCUIT DESCRIPTION
An engine coolant temperature (ECT) sensor monitors the temperature of the coolant. This input is used by the powertrain control module (PCM) for engine control and as an enabling criteria for some diagnostics.

The air flow coming into the engine is accumulated and used to determine if the engine has been driven within conditions that would allow the engine coolant to heat up normally to the thermostat regulating temperature. If the coolant temperature does not increase normally or does not reach regulating temperature of the thermostat, diagnostics that use engine coolant temperature as enabling criteria, may not run when expected.

This diagnostic trouble code (DTC) will only run once per ignition cycle within the enabling conditions. If the engine coolant fails to reach a preset target temperature before a calculated air flow is accumulated, DTC P0128 will set.

CONDITIONS FOR RUNNING THE DTC

DTCs P0105, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0122, P0123, P0125, P0130, P0131, P0132, P0171, P0172, P0201, P0202, P0203, P0204, P0300, P0301, P0302, P0303, P0304, P0325, P0336, P0420, P0440, P0442, P0446, P0452, P0453, P0480, P0502, P0503, for automatic transmission only, and P1441 are not set.
The engine has run more than 30 seconds and less than 20 minutes .
The minimum intake air temperature (IAT) is more than -7°C (19°F) .
The engine coolant temperature at start up is less than 65°C (149°F) .
CONDITIONS FOR SETTING THE DTC

The average air flow is more than 20 g/s .
The vehicle has traveled more than 2.4 km (1.5 mi) over 40 km/h (25 mph) .
Enough air flow has entered the engine and the engine coolant temperature has not risen to 80°C (176°F) for 30 seconds .
ACTION TAKEN WHEN THE DTC SETS

The control module illuminates the malfunction indicator lamp (MIL) if a failure is detected during 2 consecutive key cycles.
The control module sets the DTC and records the operating conditions at the time the diagnostic failed. The failure information is stored in the scan tool Freeze Frame/Failure Records.
CONDITIONS FOR CLEARING THE MIL OR DTC

The control module turns OFF the MIL after 3 consecutive drive trips when the test has run and passed.
A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant reaches a temperature that is more than 70°C (158°F) during the same ignition cycle.
Use a scan tool in order to clear the DTCs.
DIAGNOSTIC AIDS

A DTC P0128 is designed to detect a faulty thermostat.
A skewed IAT sensor may cause this DTC to set.
TEST DESCRIPTION

DTC P0128 - Steps 1-7

DTC P0128 - Steps 8-11

The numbers below refer to the step numbers on the diagnostic table.

This step tests for excessive resistance in the ECT circuit.
This step tests for a skewed sensor through the range of temperatures affecting this DTC.

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3

Hey a1amap! just went through the same problem with my fiance. she has a 2004 ford explorer and it was overheating. what happens most of the time is the thermostat gets stuck closed and the coolant cant cycle making your vehicle overheat also the smell could be the coolant where its hot also from the thermostat getting stuck. If you could check the thermostat housing when my fiances went up it blew out her seal on the lower housing unit both thermostat and housing was not too hard to fix. good luck and i hope this helps!

Ryan

4

That sweet smell is the samthing that makes dogs drink antifreeze. You probally have a collant leak and you smelled the burst of pressure releasing. As for your oil pressure bouncing that’s because the oil pump is mechanicalnwhich means it spins as fast as the rpm’s of the motor,so at idle its low, and hhighway speed its higher.

5

Sounds like t-stat stuck open, just replace it and clear code.

6

+1 on the help!

Sensors are cheap and easy to replace, I’d swap them out before doing anything else. I agree that the smell was a pocket of antifreeze that got too hot due to non-circulation and vented all at once.

7

Wow that was a lot of replies
I am going to start with the tstat for a couple reasons. First it is the least expensive option. While replacing the tstat I will drain the radiator fluid which may cure the pressure gauge flux if it was caused by an air bubble.
An air bubble would explain a pressure release and the smell but also another problem that I originally thought was unrelated. The Ac on the car is not cool at idle. As soon as you accelerate it beomes cool. Originally I thought the coolant level was low but it was not. The I figured it was 8 years old and may need to be charged. An air bubble would cause the same symptoms.

Thanks for all the replies.

8

No problem! good luck

9

You def have the right group here for auto questions…

10

Before I could replace the tstat and flush the syatem (about 20 starts) the light went off on its own. I think the air bubble causing a pressure release is right on the money. I still had the cooling system flushed for 2 reasons. For $99 I had it flushed for me. Its been 8 years and it was time. If I flush the system myself I would have to put in over a gallon of coolant, use a water flush and collect and dispose of the waste. I had the connection to tap into the coolant line but its a pain to dispose of more coolant then you purchased from a store.

Should be good to go now.

11

I used to take my old coolant to Sears automotive shop to add to their recycle sump. they used to be pretty good about it. or you can jug it and take to the fall Hazardous Waste Collections. But you are right, its much easier to have the shop do it. plus they do a much better power flush. mine is due too. 2005 saturn , original coolant. even though theres only 54,000 miles on it, its antioxidants get used up . time for a fresh change.

You may have had a sending unit problem too. loose connection, faulty sending unit.

12

It is a thermostat sticking open. See this on those and Colorados all the time. Will likely reset code once ambient temperature gets cooler. We only use AC delco or Gm thermostats due to high failure rate of aftermarket t-stats.
Mike

13

It came on again shortly after I had it flushed and it was on a rather cool night. I replaced the TSTAT last weekend with an AC Delco. No light yet…