I’ve had my 2004 automatic 350z for about 10 years and it has been running great, a California car, and always kept in my garage when not in use. About a month ago I got a check engine light for the first time ever -- cylinder 1 misfire. Cleared the code and drove it awhile and got the same thing again so took it in to get the coil pack replaced and 3 of the spark plugs. The mechanic replaced those (OEM parts)... but then it refused to start back up for him.

He said the security light hinted at an immobilizer problem or a key mismatch. He replaced the immobilizer and rekeyed my keys and it started up once, but then never again. Then he said he’s not good with electrical, and it could need a new computer or something, so I should take it to a dealer.

I transferred it to a Nissan service center and they say now that there is a “short somewhere within the communication system, that the communication high and communication low should only be receiving 2.5 volts per system but they are receiving 9 volts. So there is a short somewhere in the wiring harness.”

Has anyone else had a short like this happen, and how was it resolved? The dealer shop is saying this could be extremely expensive to diagnose and fix. It seems strange that this all happened so suddenly, and while the car was in the shop for something so simple. Sounds like it could be 20+ hours of labor in the worst case scenario so I'm not sure how to proceed given the car's advancing age.

 

I would start by checking the resistance of the coils. Terminal 1-2, 1-3, 2-3 Shouldn't be 0 or infinity.
and maybe opening up that harness that he touched/looking for chew marks

 

The one time it started did it run correctly? Does the red light above stay solid and only cranks but doesnt start? If so, its probably the all too common NATS failure. NATS delete via Uprev is the go to solution once NATS fails.