Reset ECM - Bonneville.

[scottyb]

I am helping a buddy with his 99 Bonneville. We want to reset the ECM to see if it codes again after our repairs. Can we reset the ECM without disconnecting the battery?

 

[gofstbuick]

Have you looked at freeze frame data, prior to resetting the ECM? Yes, you can disconnect the battery to reset the ECM, but you'll loose OBD2 freeze frame data and all monitors will return to "not run". Once the monitors return to "not run", you'll have to perform the drive cycle to re-run the monitors. Also, if there are security codes for the sound system, the dealer will have to set those up for you. It would be better to erase the ECM using a OBD2 scanner. But, then again, if you have not recorded or viewed freeze frame data, then how will you know what engine parameters se the code?

 

[scottyb]

He said the light came on this morning, but also noted temp hotter than normal, as did I when I checked it out. It took a gallon of coolant for me to top off the radiator, and now it runs cool again. We took it to AZ and the code was Cyl #6 misfire. My first assumption is it was hot enough to misfire and set the code. I want to reset the code before we start replacing plugs, wires and coilpacks.......

I have read some places that the SES light will go off after 3 cycles without the code condition. Is this true? If so, then no need to reset the ECM.

 

[gofstbuick]

Misfire is a continuous monitor. Was the light flashing? Meaning type 2 higher misfire? If so, since you installed coolant, is the light constanly on? A type 1 misfire will still record freeze frame data for the specific cylinder and you should be able to recreate the rpm and load scenario, to determine if the misfire is still present. If not, then and only then would I clear codes. The more desireable method would be to use a OBD2 scanner.

 

[scottyb]

I'm gonna have him drive it a few days. The SES light is solid, but the engine is smooth as glass. You're saying that if he reproduces the same driving condition and it doesn't misfire, then it will turn off the SES? In other words, it hits the same frame with normal conditions.

 

[gofstbuick]

Eventually, the light will extinguish, if the vehicle is driven on three consecutive trips with a warmup cycle and meets all the code set conditions without the PCM detecting any faults. But the code will remain in memory through 40 warmup cycles. A warmup cycle is a trip where the engine temperature changes 40 degrees and the engine temperature reaches at least 160 degrees. Don't you have a generic OBD2 scanner? You can clear codes with a generic scanner?

 

[scottyb]

We had Auto Zone scan the code. I'm just gonna let him ride for a while and see what happens.

Thanks for your help.

Scott

 

[gofstbuick]

sent you email

 

[scottyb]

He's taking it to the stealership.

2 more rough cold starts, and a gallon short of coolant at lunchtime today. I topped off the water, had him start it, and got just a few good whiffs of exhaust - burning coolant. I hope for his sake it's just an intake issue and not a headgasket. Oil is clear.

 

[TurboJim]

Cyl 6 mosfire and loss of coolant tells me the upper plenum is cracked under the EGR passage and is allowing coolant in the engine. This coolant upon start or restart will cause the engine to misfire until the coolant is burned.

This explains the misfire AND loss of coolant.

This job is now called the 3800 tune up in my shop. VERY common.

Jim