Nissan V35 Skyline P0350.
A customer of mine has a Nissan V35 Skyline with the 3.5-litre GQ35 V6 engine
He came in with the malfunction indicator lamp (MIL) on and after a thorough inspection of the secondary ignition we found one of the ignition coils was failing under engine load. A misfire was also noticed on a road test and the faulty coil was replaced. Nissan V35 Skyline P0350 code was set.
The customer asked that the other five coils not be changed because they are reasonably easy to get to and to replace. The car was good for 12 months.
But then the car came back with the same dreaded P0350 fault code (ignition-coil primary/secondary-circuit malfunction). Unlike last time, there was no noticeable misfire when driving and we could not fault the coils on our lab scope. Even the spark looked good and seemed healthy.
Now I could have simply thrown a new set of coils in the car and the problem would have been fixed. However, this was not going to teach me why they all looked good yet we still had the code. Besides, we could have a feedback problem causing the engine control unit (ECU) to log this code or we could even have an ECU issue. I had to be sure why the car was logging the code and, even though I suspected a faulty coil, I was not about to just throw a set of coils at it without good reason.
Sent all of the coils to Rod Maher.
I sent all of the coils to Rod Maher in Grafton, who used his coil bench-tester to stress them out. He found two were leaking in the secondary-coil spark-plug boot. You see, Rod not only stresses out the coils but runs a incandescent test lamp that is earthed to ground – waving the pointed end over the coil boot will bring out any weaknesses the boot may have.
We replaced those two coils. I also checked them on a running engine with a spark tester set to about 35 kilovolts (kV) – using my test lamp the way Rod does – and one of the two was leaking. The other, I found out later, started to break down at 40kV when passing the pointed test lamp past the coil boot.
We cleared the code, road-tested the vehicle and retested for codes. All seemed good. The customer paid for the job and even said how much better the car seemed to drive.
But then, two days later, there was another phone call. The engine light had come back on.
Sure enough, the MIL light was on and we had our dreaded P0350 code again. This time the code would clear but reset as soon as the engine was running. There was no misfiring but it was clear whatever was setting the code was now constant and should make my job easy.
After checking each coil’s primary current and not seeing any evidence there, I retested each coil using the spark kV tester set to 40kV. Every coil passed the running test using a test lamp and did not show any leakage.
The spark plugs were only a year old but we had to rule them out, so a new set went in. There was no change.
Nissan V35 Skyline P0350 code – possible causes
• Faulty ignition-coil primary.
• Faulty secondary ignition-coil primary.
• Open secondary harness or shorted ignition-coil primary.
• Poor electrical connection of secondary circuit.
• Faulty engine-control unit (ECU).
It seemed the only thing left was to check the ECU coil-feedback signal that goes to and from the coil. If the signal was there and all was good we would then have to check the ECU powers and grounds. If they were OK then the problem would have to be the ECU.
Pico scope pattern
I hooked my scope up and checked the three right-hand-bank coils first. All voltage coil feedbacks looked the same and even voltage was going to all coils. When I repeated the test on the left bank, however, one of the feedback voltages was noticeably higher than the other five coils that had been checked.
There were two possible causes for this – it could have been a coil or a voltage leakage in the ECU. So I got out one of the old coils that we’d replaced earlier, swapped it and rechecked the voltage. This time the feedback voltage was normal. The code was cleared and did not return.
Finally, I had the confidence to replace the rest of the coils. Should I have replaced them all at the beginning? Of course I should have. That means I have to ask myself another question – do I give my customers the choice or do I take that away from them by telling them all of their coils will need replacing. In the future I think I’ll be strongly recommending all coils get replaced.