Code P023, Ignition Control Circuit Problem: Action

PCM turns on MIL and will not enable spark timing control. Engine will start and run on base timing. PCM disables EGR solenoid. Transaxle shift adapts are maintained at current levels.

1. Checks if Code P035 is set. A REF LO problem can cause other ignition problems.
2. Checks if Code P023 was set during engine crank or while engine was running.
3. Checks for short to voltage on circuit No. 424. Checks if PCM failure is causing ignition control system into by-pass spark control when it should not be.
4. Checks for open in circuit No. 423 to see if ignition control pulses are reaching ignition control module or if pulses are reaching ignition control module but ignition control module is not reacting.
5. Checks for short to voltage in circuit No. 424.
6. Checks if by-pass control is being sent by PCM to ignition control module. If by-pass control is being sent, voltage will be greater than 4.1 volts.
7. Checks if by-pass control being sent by PCM is being received by ignition control module. If circuit No. 424 is good, resistance will be less than 5 ohms.
8. Checks if PCM is providing proper signal to ICM. If PCM terminal 3F3 has 30-100 Hertz, PCM is not at fault.
9. Checks if PCM can produce proper ignition control pulses. If maximum voltage exceeds 3.7 volts, PCM is okay and ICM is at fault.
10. Checks circuit No. 424 for short to ground.
11. Checks if ICM is able to recognize a by-pass signal. If it does, Code P023 will not set again. If Code P023 resets, the ICM is faulty. If does not reset, PCM is faulty.
12. Checks if ICM is causing incorrect voltage or if PCM is supplying incorrect signal.

Fig 1: Code P023 Schematic, Ignition Control Circuit Problem

Courtesy of GENERAL MOTORS CORP