My 1999 Nissan Maxima has a service engine soon light came on. The trouble code was P-1320---(Primary Ignition signal or misfire) I was told when I had this trouble before that the ignition coils on the Maxima need to be replaced. I only replaced the #5 ignition coil when I took it to the dealer to troubleshoot the problem. They also suggested that I replace all the coils. These coils are very expensive and I decline and only changed the #5 coil. Now I have changed them all and erase the code with the tester I purchased, and the light returns after a few minutes. What other components should I be looking at?

My 1999 Nissan Maxima has a service engine soon light came on. The trouble code was P-1320---(Primary Ignition signal or misfire) I was told when I had this trouble before that the ignition coils on the Maxima need to be replaced. I only replaced the the #5 ignition coil when I took it to the dealer to troubleshoot the problem. They also suggested that I replace all the coils. These coils are very expensive and I decline and only changed the #5 coil. Now I have changed them all and erase the code with the tester I purchased, and the light returns after a few minutes. What other components should I be looking at?
The fault may be actually in the ECM itself. The driver's for all the coils is controlled by the ECM. If the ECM "thinks" it is requesting an ignition firing, but not seeing that coil fire, based on crankshaft speed variation, it will fault the coil erroneously.
Find a known good ECM (from a junkyard perhaps?) and retest.

Try replacing the spark plugs with the same brand and plug number that originally came with the car. Platinum plugs frequently need to be replaced at about half the recommended mileage.