Code P025, 24X Reference Signal Low: Action

PCM turns on SERVICE VEHICLE SOON light message.

1. Checks to see if Code P035 is present because REF LO problem can cause other ignition problems.
2. Checks ability of ignition control module to produce 24X reference pulses. If system is operating correctly, reading will be 200 Hertz or greater.
3. Checks to see if ICM is providing PCM the proper 24X reference signal.
4. Checks for open or short to ground in circuit No. 647.

Fig 1: Code P025 Schematic, 24X Reference Signal Low

Courtesy of GENERAL MOTORS CORP

Fig 2: Code P025 Diagnostic Flow Chart, 24X Reference Signal Low

Courtesy of GENERAL MOTORS CORP