Have a stock 1994 Z28 with 90,000 miles.The service engine light had come on ocasionally over the past year but always went out after a few miles. It finally flat out died on the road. I got it started after it sat for a day. Figured it needed a new Opti-spark, so I replaced withnew one, water pump,plugs, wires. It fired upbut I still have the SES light and itcranks a lot before starting. Took it out for test drive and it died again. Got it restarted and found instructions to retrieve error codes. Problem is that it won't go into diagnostic mode, although the fan does run. SES light comes on but does not blink any codes. It has the 12 pin connector, not the 16. Now the battery is dead from fan running. Other thing odd is the fans com on and stay on right after start-up too. Wondering if I have a temp sensor problem?

The fans usually come up when a code is set. This is part of the limp mode program to prevent engine damage. You cannot flash code on a 94, you need a OBD1 scan tool with an OBD2 cable.

Thanks for the reply. Got it running with a new coolant temp sensor. Still confused on the diagnostics. This car has the OBD1 12 pin connector. I should be able to retrieve fault codes by jumpering A to B as per the manual and everthing elseI have read?

I never had any luckflashing the codeson my car either. Had to use a scan tool.