I ran my scan tool and had a pending code. Since I had the previous problem of a wet coil I wanted to clear the ecm. So I went - disconnected the neg battery cable, stepped on the brake and went to bed for the night. Some 8 hours later I reconnect the battery cable (I stuck a key in the ignition so as to not cause the neighbors to think the car was being broken into with with the security alarm going off). I reconnected got in the car and it wanted, as expected) to set the parking breaking. The A and B mileage meter was reset to zero. The clock was reset. My radio stations held on, but had to reset tone levels on all bands/cd and reset the climate control. However when I started the car and then turned off, i ran the scan tool on the KOEO mode and it showed the same pending code and showed the IM tests that had been previously ran. Of course, I erased the codes, but wondered why they still showed after an 8 hour reset.

Do I need to locate the fuse to the ecm and remove it as well or do I need to disconnect the positive side of the battery as well or did I reset correctly and the codes stayed a part of the ecm by default and now once removed the car will go back to learning properly???

This, I know is a very basic and simple question and perhaps everything went normally and I am just being stupid, however I would assumed the codes should have been gone from the ecm or am I incorrect on that assumption.

Thanks - as always for your expert type assistance.

Tom in Dallas

2005 S-Type 3.0 (75k- exactly)

 

Tom, your incorrect.

The only way to erase a code is to erase it through an OBDII scanner or have enough successful warm up - drive cycles where the "pending" or "flagged" code does not get picked up by the PCM.

Hope this helps....

 

Not really and I do not mean this is a rude sense, but this I already know. As I indicated above ( Of course, I erased the codes, but wondered why they still showed after an 8 hour reset).

My question is this- if before I do a reset of the ecm, I use my ODBII scanner and see pending codes or 4 completed and 3 inc IM's or whatever, if I do a hard reset as I thought I had done, should all of that had disappeared from history and force the ECM to re-learn or is the fact that they stayed in the volatile memory of the ECM and I had to erase with a scanner, mean I did not reset the ECM completely???

Thanks

Tom

 

I understand you can clear learned engine settings by the hard reset but need an OBD tool to clear codes. You should always have a pending P1000 after that and it should turn into a P1111 after enough relearning - if there are no faults stopping that. In the latter case you may not get codes flagging and may also not get the monitors to complete, in which case diagnosis can be awkward! (Which is why ideally you only clear codes after you believe the cause is fixed.)

 

Thanks= that is my answer. I just found it strange and ha not paid attention until this time about resetting the ecm ad then looking at the ecm through the scanner,. I assume that 8 hours without power is sufficient and that since I have reset codes to default (zero- so as to speak) by scanner) I have done the reset.

Thanks again

Tom in Dallas

 

Tom- disconnecting the battery will not erase OBDII codes so there's no benefit doing so. The delete codes function of your scanner is the sole method of erasing them AFAIK.

 

Tom, no harm, no foul - again, any code after a reset (besides P1000 or P1111) means the fault is still present... whether pending or stored...

 

The good thing about a hard reset (battery off) is when you want to clear emissions-related learned values (in "KAM") such as after fitting a new O2 sensor. OBD code clear won't clear KAM.