Thread: Service Engine Light on; But car runs fine

Ok so I have a 2000 Pontiac Grand Prix GT. A few months or so back, the service engine light came on while I was driving. The car didn't stutter or do anything funny, it ran perfectly fine. It did so the whole time the light was on. I had stopped driving it for a few days with not knowing and when i finally got in a drove it, less then a mile just around the street I live on it went out. It hadn't come back on, still ran fine then all of the sudden yesterday it happened again. I was driving and all of the sudden the service engine light came on yet again. Car didn't do anything funny and is still running perfectly fine.

Any ideas as to what would cause it to do this?

I know my AC compressor is going out but doubt it would cause it to come on.

Get the car scanned to see what code its throwing.

Autozone and other parts store can scan car codes for free.

I must have a fail autozone near me, they say they don't do it ._. looks like its off to pepboys lol.

Your car is probably getting ready to explode.

Codes Came up

P0128
P0742
P1629
P1811


And if my car explodes i would honestly not be shocked

P0128 is a Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature) code. Probably need a new thermostat.

P0742 is a Torque Converter Clutch Circuit Stuck On code. I can't tell you what to do for that one besides check your tranny fluid.

P1629 is apparently a theft deterant system code? No advice for you on that one.

P1811 is a code for the abs or wheel speed sensor I guess so you must have a bad hub or wiring or something.

Thanks burgundy.

I checked the tranny fluid and it full and looks brand new. I haven't noticed it running any cooler then normal but I may take it out to see. I don't know much about the theft fuel-enable one except to know if it could be it or not. And it doesnt shift hard, make funny noises when shifting or anything.

I am tempted to just replace my thermostat and well if it goes off sweet if not well at least i know i have a new thermo haha.

DTC P1811 Maximum Adapt and Long Shift
The 1-2, 2-3 or 3-4 shift is longer than 0.7 seconds, twice in one trip.

DTC P0742 Torque Converter Clutch (TCC) System - Stuck On
The TCC release switch is closed, which indicates that the TCC is applied, 6 times for 4 seconds each during one trip.

DTC P1629 Theft Deterrent Fuel Enable Signal Not Received
The ECM has not received the fuel enable password from the BCM within 1 second .

DTC P0128 Engine Coolant Temperature (ECT) Below Thermostat Regulations Temperature
An ECT sensor monitors the temperature of the coolant. This input is used by the control module 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 vehicle has been driven within the 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 the regulating temperature of the thermostat, the diagnostics that use ECT as enabling criteria may not run when expected. If the control module detects the calibrated amount of air flow and engine run time have been met, and the ECT has not met the minimum thermostat regulating temperature, DTC P0128 sets.

Thanks Seachicken.

I'm going to have to get it on he freeway so I can get a feel for the shifting between gears. Other then that gonna end up taking it in to get the problem more pinpointed.

This car just has me at a loss since it is running no different then before.

One thing you aren't taking into account is.. which codes are old and which are current.

When 1811 sets your transmission will slam into gear. You will definately not question if it slammed into gear, you will know. Also this code does not turn on the SES light.

P0742 usually causes your car to stall if the TC is actually locked on.

P1629 is going to cause the car to start and stall out. Typically working the key a couple times will fix this issue. Or replacing the ignition. I think this only sets the security light to be pissed at you once. Although since we all ignore that light... we never know it's mad until it's on solid.

P0128, you should be able to see this on your temperature gauge. Likely it's the only current code that is causing the light to come on. Does your car take a long time to heat up, using more fuel than usual....

If you don't have any of the above symptoms, drive the car further and have it rescanned in a few days. Whatever code you have....it'll come back.

Thank you so much Bill.

Well then I know its definitley not the P1811,0742 or 1629 as the car has none of those symptoms at all. I took it out today and it didn't seem like it was warming up like it normally woul or get to the temp it normally would. As well, i do seem to use more fuel then normal. Gonna take it out for a farther drive to see and really get a good read on the temp but by what you say, I'm gonna bet its the thermostat.

I say skip the extra drive. Buy a thermostat and seal. Remove the two 10mm bolts while it's cold and lift the housing up. Clean your surfaces, swap the stat and put the housing back on with a light amount of RTV on it. Refill the radiator for the cup or two of coolant it lost.

Drive and smile.

Gonna take your advice and just skip the drive and go ahead and replace the thermostat.

Thanks a ton for the info bill

Sweet it went off!

if you have access to a scan tool clear the codes, some dtc's can take 100 drive cycles to clear. im not sure what a p0128 req's

I dont have one or know anyone with one. Im going to invest in one Though I think lol.

I disconnected the Battery left it off a few, reconnected it and the light was off.

Thanks all for the help!