Hi Rich here, new member and thanks for having me. I just replaced the knock sensor on a 1999 and have been popping code 1401 after that. For those of you who get a 1401 code which is the egr temp sensor. Check the harness going to the sensor, I had a broken wire to the sensor tripping the code. Easy fix. in this pic you can see the connector which goes over the top of the motor to the connector for the temp sensor. There was a break there. Shown is the wire tied together to see if the code cleared, it was soldered and shrink tubed for a permanent repair. For reference, you can see the gas filter in this pic so you can Easily locate the connector. Regards Richy