Help needed on 94 with code issues....

[coves4me]

OK, I solved an aftermarket radio issue by installing the resistors and diode and that made the C72 and H72 codes vanish. I jumped the #4 and #12 pins on the connector under the dash and I still get a C42 code in the "A" module, the Derm (airbag) module. This is a non-issue as I could care less about the airbags and whether they work or not. BUT, my brand new OEM cooling fans still run continuously and the Service Engine Soon (SES) light still illuminates continuously with NO other codes showing. I'm puzzled. I've replaced the MAF sensor with a new AC Delco replacement, the ECT sensor has been replaced, the MAP sensor has been replaced, the EGR valve and EGR vacuum solenoid are new, a new AC Delco fuel cap was installed, a new fuel filter was installed, a new fuel pressure regulator was installed, the catalytic convertors have been replaced and the O2 sensors were replaced the Denso types. Now, I've got new AC Delco O2 sensors to install, but there are no codes showing that indicate the Densos are throwing the SES light. Could the Denso O2 sensors be throwing the SES light with no codes? I'm puzzled and could use some help. Thanks in advance.

Mark

 

[Hib Halverson]

If the MIL is on and the fans run all the time, there is one or more fault codes set in the ECM.

1) Stop "throwing parts" at the problem because in some cases you're probably wasting money.
2) Obtain the Factory Service Manual and use its trouble shooting information.
3) Get a scan tester which supports OBD and read the ECM codes.

A 94 will not display ECM fault codes using flash code diagnostics and may not display ECM codes via the IP display. Also, there may be ECM codes which are only readable by a scan tester.

For more information on ECM diagnostics see:
Corvette Action Center | Tech | A Dose of Digital: Part 1 - The Basics - Page 1 of 5
Corvette Action Center | Tech | A Dose of Digital: Part 2 - Diagnostic Tool Buyer's Guide - Page 1 of 4

 

[coves4me]

Hib, thanks for the input. I read your articles and they were very enlightening. I borrowed a buddy's Actron 9145 scanner and pulled the codes. Guess what, there were none and the SES light remained on. I used the scanner to clear the codes, disconnected the neg. battery cable for about 5 minutes, then re-connected it and the SES light continued to remain on. Based on what I'm seeing it looks like the PCM may be faulty. Oh well, gotta love these money pits!!!!

Thanks for your help.

Mark