Why is my car running fine, but the check engine light came on? The code reader I have shows ISO9141. This is a 2002 Chevrolet Cavalier Sport model.

Hello:

ISO9141 is not a Diagnostic Troubleshoot Code, it is a protocol language used by car manufacturers.

There are basically 5 types of language protocols used by auto manufacturers:
1.) J1850VPM (Variable Pulse Width Modulation at 41.6 Kbps)
2.) J1850PWM (Pulse Width Modulation at 10.4 / 41.6 Kbps)
3.) ISO 9141-2 (Asynchronous serial communication at 10.4 Kbaud)
4.) ISO 9141-2 and KWP2000 (Asynchronous serial communication at 10.4 Kbaud)
5.) ISO 15765 CAN (250Kbps or 500Kbps)

What does this mean to you?
It means that each protocol differs electrically and by communication format.
The Code Reader or Scan Tool you are using must be compatible with the vehicle's specific protocol in order to communicate.

So if your reader is not ISO9141 compliant- you will never be able to pull the codes from the OBDII module.

Hope this explanation helps.

Hi, that is diagnostic protocol not a trouble code. According to my information.