Hey guys so i bought this 1991 300zx I went to get the car smogged but they said it was going to fail due to a functional test ... they stepped in the car turned the switch on and said the check engine light was not lighting up .. i took it to a mechanic and he said the bulb was fine so my question is ... anyone know what could be going on ? what to check for ? possible fuses ? i tried plugging in my machine so it can communicate with the ecu but it cant connect ? anyone with any info i would really appreciate it i want to sell the car but i don't want to sell it knowing its not going to pass smog. Just for the record the car turns on and idles fine runs fine etc...

 

Welcome to ZDriver!

Z32s are not my thing. In a Z31, first thing I would check is the ignition switch itself. They get worn or corroded over time and need to be replaced. No big expense if you go aftermarket.

Also suspect the harness connections to and from your ECU. Disconnect them, clean, dry and reconnect. Seems to me the ECU would have to monitor all of the sensors involved in turning the Check Engine system on and off. If your factory service manual electrical diagrams are available (XenonZ32.com Reference) you can multimeter the feed to the warning light when you turn the key on. If no power at the light, start tracing backwards to find where the circuit goes dead. Let us know what you find. Thanks.

 

I'm assuming you live in California? Because nowhere else on earth would be so picky about a CEL that doesn't matter at all. It's only 96+ cars that are subjected to the CEL working or not. I'd personally find another shop or do some smog law research. You can also run an ecu self diagnosis to see if it spits out any codes.