DTC P012: No 4X Reference Signal From Ignition Control Module: Action

• PCM turns on the "SERVICE ENGINE SOON" MIL.

NOTE: Numbers in list refer to circled numbers in diagnostic flow chart, see Fig 1. For circuit identification see Fig 2.

1. Check to see if Code P035 is set because a REF LO problem can cause other ignition problems.
2. If Code P012 is current, the condition still exists and can be diagnosed directly. If Code P012 is history, look at snapshot data to determine conditions under which code was set.
3. Check for proper output of the Electronic Ignition System. If the voltmeter reads 4.1 volts or greater, the Ignition Control Module is able to produce 4X reference pulses.
4. Checking to see if Code P012 was set while the vehicle was running or not, if MAP value is 80 kPa or less vehicle was running at code set. Stray CAM pulses at key on engine not running can cause Code P012 to set falsely.
5. Checking for 4X reference pulses on CKT 430 from the Ignition Control Module to the PCM. If PCM terminal "3E2" has between 30 and 100 Hertz, the PCM is receiving 4X reference pulses.
6. Checking if a faulty PCM is pulling the 4X signal low.
7. Checking for short to voltage on CKT 430.
8. Checking if ICM is providing proper reference signal to PCM.

Fig 1: PCM DTC P012: No 4X Reference Signal From Ignition Control Module Flow Chart

Courtesy of GENERAL MOTORS CORP.

Fig 2: PCM DTC P012: No 4X Reference Signal From Ignition Control Module Flow Chart Circuit

Courtesy of GENERAL MOTORS CORP.