Question

check engine is on and codes p1320 and po138 were detected, also KOER Fail. what needs replacement for a Maxima 2000

Answer 1

The repair for the 1320 code is replacement of all 6 ignition coils, however on this year model if you wait long enough it will generally throw a misfire code for the specific cylinder that is causing the issue.

The P0138 is for the rear heated O2 sensor. In most cases replacing the sensor will resolve the issue.