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GM-midsize-guy

Check engine light that stayed on ... but is no longer lit up anymore

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I've got a 2008 base Buick LaCrosse with a 3800 Series III V6 and under 50,000 miles.

 

I got an oil change last week. The next day, the check engine light went on. I was wondering what they might have messed with at the dealership that possibly loosened a connection or knocked out a sensor. It was purely a coincidence.

 

I went to an auto parts store. They scanned it with the OBD II device as a courtesy and it kicked out code p0128. This means "Engine Coolant Temperature (ECT) Below Thermostat Regulating Temperature." I was thinking that, most likely, I would be replacing the ECT sensor (not an expensive sensor) or the thermostat was stuck open.

 

Tonight, when I drove off, the checking engine light went off. And it has stayed off. When the light went on, we had had a cold snap. Today, it was about 20 degrees F warmer outside. I'm wondering if this had anything to do with it and if I can ignore the issue.

 

What do you think? Have you had check engine lights that came off and then sort of went away? Also, have you heard of this particular issue and could it have been caused a big drop in the temperature outside?

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in those conditions...... with no other information available to me, I would assume the thermostat might have gotten stuck at least partially open.

 

generally, GM sets up the conditions to test for something like that intelligently, so that it would account for an extremely low ambient temp, but sometimes..... mistakes happen, if they get discovered a new calibration is released and life goes on. you could also have inadvertently caused it to be falsely triggered if you had a drive cycle that was JUST on the borderline of normal, like if a minimum startup coolant/air temp threshold was met while inside of a garage where ambient temps could be at least warm enough to do the test, then the test is done while out in the open...

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P0128 is a thermostat code. The thermostat is either getting stuck open OR the engine wasn't allowed to heat up, which also causes this code to set, and turns off the temp gauge (don't know if you noticed that).

 

I drove my 3800 Camaro without a thermostat this summer. It didn't like running at 130F in the morning, which made it throw that code. Cleared the code in the afternoon, engine heated up to 160-180 and I didn't have to worry about that code until the next morning. I eventually put a thermostat in, and issue disappeared.

 

Moral of the story is that it wouldn't hurt to change the thermostat, but if the engine has trouble reaching 190-210, then the PCM is going to throw that code because for some reason, the 3800's PCM doesn't like being ran anywhere below or at the 160 mark

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I'm back with an update/question, and it sounds like the last 2 posters had the same issue, with sensor lights that went away.

 

I got that p0128 code about 2 months ago, when I first posted. It then went away. It's related to the either the coolant temperature sensor or the thermostat is (partially) stuck open.

 

It has come back twice ... and gone away twice. It went away today after being on for about 3 days. It seems like, when it's over 50 degrees F outside, it stays off.

 

I'm going to ignore it. The coolant temp. gauge looks very normal. The coolant was flushed a year ago. Would you ignore your sensor light if it was intermittent and it didn't affect drivability in the least?

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It went away because it cleared it's self.

 

My Lumina is currently doing that, sadly auto stores wont do a free ODB2 check for me to see what it is.

 

I do about 30 of them a day and print customers off with all the information AutoZone`s system has for the code including recommended things to look at. Stores must suck where you live or you don't have a AZ. All for free unless offered a tip.

 

I'm back with an update/question, and it sounds like the last 2 posters had the same issue, with sensor lights that went away.

 

I got that p0128 code about 2 months ago, when I first posted. It then went away. It's related to the either the coolant temperature sensor or the thermostat is (partially) stuck open.

 

It has come back twice ... and gone away twice. It went away today after being on for about 3 days. It seems like, when it's over 50 degrees F outside, it stays off.

 

I'm going to ignore it. The coolant temp. gauge looks very normal. The coolant was flushed a year ago. Would you ignore your sensor light if it was intermittent and it didn't affect drivability in the least?

 

T-stats are cheap, might as well replace it

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the way you're describing events, it's almost certainly the thermostat..... and while it's sticking somewhat open now, what happens once it starts sticking closed?

 

I think you're right. With the weather warmer and staying at 50F or more, the check engine light is off. However, I expect this situation to rear its ugly ahead another time or two, because it's still winter.

 

I'll go ahead, get some estimates, and get it done.

 

I know it's an easy fix but I don't like fumbling around the engine compartments of newer cars with advanced electronics. I changed the thermostats on 2 of my dad's cars, one with a 250 c.i. (Chevy built) inline 6 and another with a 260 c.i. (Olds built) small block V8. Piece of cake: just plug wires and a few vacuum hoses in those cars that he kept forever, sitting right up front and looking straight at you, almost begging to be changed.

 

Thanks for pointing this out.

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