P025

Diagnostic Trouble Code Chart P025:

Ignition Control Module Circuit:

CIRCUIT DESCRIPTION
In this diagnostic test, the Powertrain Control Module (PCM) checks for 4X reference pulses being received without 24X reference pulses. When the engine is running and the PCM is receiving 4X reference pulses without 24X reference pulses and the 24X reference signal line is low for 4 seconds, Code P025 is set.

TEST CONDITIONS
1. Codes P035 and P041 are not set.
2. A CAM reference pulse was received.
3. Engine speed greater than 496 rpm and less than 1200 rpm.
4. Ignition control not in bypass.

FAILURE CONDITION
1. No 24X reference pulses received by the PCM and the line is low for 4 seconds.

ACTION TAKEN
1. PCM turns "ON" the "Service Vehicle Soon" message.

NOTES ON FAULT TREE
1. Check to see if Code P035 is set because a REF LO problem can cause other ignition problems.
2. Check ignition control modules ability to produce 24X reference pulses. If system is operating correctly, you will measure 200 Hertz or greater.
3. Checking to see if Ignition Control Module (ICM) is providing PCM the proper 24X reference signal.
4. Checking for open or short to ground on CKT 647.