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Discussion Starter #1
So I posted a thread on this a while back.

Well my coolant gauge used to malfunction intermittently. It would sometimes go out while driving. Other times it wouldn't work from starting the car. Well it stopped causing problems for a few months.

Now the problem has come back around. I noticed it would drop to 0 or "100 degrees" when I would be driving and changing the air flow (head, feet, defrost, etc) Well now today the gauge has yet to come on at all. The fans are blowing at full blast. AC works and heat works.

Some say it's the coolant temp. sensor. Some say it's the thermostat itself. I was hoping someone would be able to tell me exactly the cause before I start chasing ghosts with the little money I have.

Also I have yet to have a check engine light come on during this problem.
 

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08 convertible
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I was hoping someone would be able to tell me exactly the cause before I start chasing ghosts with the little money I have.
If someone could do that they wouln't be on a G6 forum, LOL.

Could be bad sensor, intermittent wiring connector somewhere, issue in the gauge or cluster, etc. A faulty thermostat would give you no hot heat (if stuck open) or overheat the engine (if stuck closed).
 

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Discussion Starter #3
I finally got a check engine light. Took it to Autozone and the guy told me it's the thermostat. Said the engine temp is low.

The car is not over heating, but the fans are constantly running full blast.
 

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I wish you the best of luck... I have a 07 Malibu that has similar problems. Ive changed coolant temp sensor twice and thermostat twice, until I found that disconnecting the battery for about ten seconds gets everything going again. which ruled out the thermostat being stuck open. So the next thing I did was clean out the connector to the sensor with a small wire brush and throw some die electric grease in there. although I'm not driving it anymore, I haven't heard of any problems for a few months now.
 

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I have the same problem with my 09 G6 convertible. The fault code is P0128 when the car thinks it isn't warming up fast enough, so GM shuts off the gage and runs the fans full blast. I think the AC is also disabled. I have a bluetooth enabled OBD2 reader which can log data to my android phone. The ECT sensor seems to be fine, as does the thermostat, based on the temperature data. I've been resetting the fault code when it happens (about every few weeks). I would like to know if anyone found a REAL cause/solution for the problem. I don't want to replace the thermostat and/or the ECT sensor just to be stuck with the same problem and an unnecessary repair bill.
 

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If the engine is not warming up and is running cold, why would the fans be running at full speed? Logic would dictate to turn off the fans if the engine is cold, wouldn't it?
 

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08 convertible
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I would like to know if anyone found a REAL cause/solution for the problem. I don't want to replace the thermostat and/or the ECT sensor just to be stuck with the same problem and an unnecessary repair bill.
There isn't such thing as "the problem". It could be many different faults. In my case it was a bad thermostat. Stuck open. Your fault may be different. A good mechanic should be able to look at all the symptoms and diagnose it correctly.
 

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If the engine is not warming up and is running cold, why would the fans be running at full speed? Logic would dictate to turn off the fans if the engine is cold, wouldn't it?
No it wouldn't. The logic is that a fault has been identified, and therefore the actual temperature is assumed to be unknown. So running the fans is the default to safest mode.
 

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No it wouldn't. The logic is that a fault has been identified, and therefore the actual temperature is assumed to be unknown. So running the fans is the default to safest mode.
Granted. However, the code P0128 was identified as "Engine running cold-takes too long to reach operating temperature", not "Unknown/Inconsistent engine temperature". This code was triggered based on comparison readings from intake air temperature, engine oil temperature, and engine run time, etc. Therefore, the ECM was smart enough to determine that the engine was running cold and triggered the appropriate code, which should then make sense not to engage the cooling fans and make things worse.
 

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I have the same problem with my 09 G6 convertible. The fault code is P0128 when the car thinks it isn't warming up fast enough, so GM shuts off the gage and runs the fans full blast. I think the AC is also disabled. I have a bluetooth enabled OBD2 reader which can log data to my android phone. The ECT sensor seems to be fine, as does the thermostat, based on the temperature data. I've been resetting the fault code when it happens (about every few weeks). I would like to know if anyone found a REAL cause/solution for the problem. I don't want to replace the thermostat and/or the ECT sensor just to be stuck with the same problem and an unnecessary repair bill.
A faulty thermostat is the most common problem. But it may be something else in your case. After you reset the code, the temperature gauge is re-enabled. Check to see how long it takes for the engine to warm up. And confirm it with the heater core output. If it takes longer than normal, then the thermostat is the most likely culprit. If the temperature gauge is inconsistent with the heater output, then the ECT sensor is likely at fault. Unless you have a high-level professional scanner, it is very difficult to diagnose the problem yourself once the code is triggered and the cooling system is defaulted into "safe" mode.
 

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This code was triggered based on comparison readings from intake air temperature, engine oil temperature, and engine run time, etc.
Do you have a reference for that statement? Can you post the link? I'd be very curious to see what that algorithm looks like.
 

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Do you have a reference for that statement? Can you post the link? I'd be very curious to see what that algorithm looks like.
No I don't. It was somewhat of a guess from resourcing information on OBD system and scanner reference materials. I do know that these other parameters are measured by the ECM for whatever reason, along with amount of fuel used and the number of combustion cycles. Therefore, the ECM would then be able to estimate what the engine temperature "should be", and comparing that to the reading from the ECT sensor to determine if the engine is indeed running cold and trigger the P0128 code for "engine running cold" if necessary. If the readings are out-of-norm, then my guess is that there should be another code for "engine temperature unknown".

This is how I would design the algorithm:
If the ECM reference is Cold, and ECT reading is Cold, then no fault exist.
If the ECM reference is Cold, and ECT reading is Hot, then a possible fault exist. Trigger a code and put the cooling system in "safe" mode.
If the ECM reference is Hot, and ECT reading is Cold, then a possible fault exist. Trigger a code and put the cooling system in "safe" mode.
If the ECM reference is Hot, and ECT reading is Hot, then no fault exist.

The problem here is that under the first scenario when all indicators showed a cold engine, once the ECM triggered a P0128 code it will operate the cooling system at the maximum "safe" mode regardless.
 

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Could be bad sensor, intermittent wiring connector somewhere...
A wiring issue gets my vote.

Since the fans are on _and_ the gauge is wonky, that indicates the problem is farther upstream, towards the sensor.

I would inspect the wires near the temp sensor connector. Pull them from the loom if necessary. Look for either a broken or chafed spot on the wires. Look for a limp spot as well (indicating the wire is broken inside the insulation). Look closely at the wires where they go into the connector.

It may be necessary to remove several feet of wiring from the loom looking for the bad spot. Perhaps there's a heat-damaged spot from the harness being routed too close to the exhaust.

As for dielectric grease, keep in mind, it's an insulator, not a conductor. So it should only be applied where the rubber seals join the plastic connector housings, but not applied directly to the contacts in the connector.

HTH.

Doug

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