1995 J Series Update Manual: Overview

1995 J Series Update Manual has been revised (See attachments.) Information not included with this bulletin has not been revised.

Please make a note of these revisions in your Service Manuals.

Diagnostic Aids

^ A small amount of resistance in the Keep Alive Memory circuit may cause a no start with a functioning MIL. Check circuit J2-03 for resistance if suspected of causing the no start condition.

^ Check for TP sensor binding or sticking in Wide Open Throttle (WOT) position or intermittently shorted or open.

^ Check "THEFT SYSTEM" telltale for flashing on the Instrument Panel Cluster (IPC) If Passlock System has been activated, refer to the IPC for further diagnosis.

^ Check for water or foreign material in fuel.

^ Check for a basic engine problem (low compression, i.e., timing chain failure).

^ Verify that only resistor spark plugs are used.

^ A scan tool can be used to energize the fuel pump "ON" to check fuel pump operation and for ignition voltage at the injector harness.

Test Description

Number(s) below refer to the step number(s) on the Diagnostic Chart.

2. Diagnosis of set DTC's may lead to the cause of the cranks but will not run complaint.

3. PCM grounds will only cause a problem if all the grounds are not making a good connection. If a problem ground is suspected, the most probable place to check is where all the grounds meet at the engine block.

7. Locate and repair any shorts that may have caused the fuse to open before replacement.

8. A TP sensor that reads too high can cause an incorrect fueling condition.

9. An engine that has not been started recently should display ECT and IAT temperatures that are relatively close to each other. In warmer weather the IAT readings may be slightly higher than the ECT readings.

10. This step looks for a normal barometer reading and a change in MAP sensor values while cranking the engine. This step verifies the MAP sensor can detect the change in the manifold pressure that occurs while cranking the engine. Compare any questionable barometer readings with readings from another vehicle.

11. While cranking the engine, the CKP Activity Counter (7X reference) should increment to 255 then rollover to 0.

12. If the scan tool loses serial data only while cranking, the ignition switch is not sending voltage to the PCM while in the crank position.

13. Check for possible voltage loss to the PCM including the ignition switch itself.

14. Battery voltage should be available at the ignition feed terminal (L) of the ICM 11 pin harness connector, and the ground terminal (K), should be a good ground.

17. The CKP sensor core is a magnet, therefore it should be magnetized.

18. The CKP sensor should output a voltage near 1100 to 1300 mV as the crankshaft turns. It is possible to trigger the ICM with a voltage as low as 200 mV. If no voltage is produced, a poor sensor connection or faulty sensor is indicated.

19. The test light connected to B+ simulates a reference signal to the PCM. An injector test light can be installed and will blink for every other touch of the test light if the CKP Activity (7X reference) circuit, the PCM and the injector driver are all functioning properly.

23. If the test light illuminates while probing the CKP Activity (7X reference) circuit, the CKP Activity (7X reference) circuit is shorted to ground. If the test light remains "OFF" and the CKP Activity Counter does not increment on the scan tool, the CKP Activity (7X reference) circuit is open. If the CKP Activity Counter increments several counts when the Reference Low (cavity H) circuit is probed, the CKP Activity (7X reference) circuit is shorted to voltage.

25. Replacement PCM's must be reprogrammed. Refer to the latest Techline information for programming procedures.

26. Battery voltage should be available at the injector ignition feed circuit whenever the fuel pump power feed circuit is switched "ON" and when the PCM is receiving ignition pulses during engine cranking or when running.

27. By installing the spark plug jumper leads and testing for spark on all 4 plug wire leads, each ignition coil's ability to produce at least 25,000 volts is verified.

28. The fuel pump is turned "ON" by the PCM for 2-3 seconds after the ignition is first turned "ON". This step checks to see if the fuel pump and fuel pump relay are operating correctly and if the fuel pressure is within the proper range. Refer to Chart A-7 - Fuel System Diagnosis for the fuel pressure gage installation procedure.

30. Ignition voltage is supplied to the injectors and fuel pump for the first 2 seconds when the ignition is turned "ON" and continuously when the engine is cranked. If the fuel pump runs but the injector test light did not blink, then the injector ignition feed circuit is open between the injector and the splice from the ignition feed circuit.

31. This step verifies that the PCM is sending a signal to the ICM to fire the ignition coils. If the test light blinks, then the signal is OK to this point and the no spark condition lies in the ignition coil harness or the ignition coil that did not produce spark.

32. The ignition coil harness can easily be checked by performing the previous step with the ignition coil harness connected to the CM. Check for a voltage and ground signals to the ignition coils at the ignition coil electrical connector.

33. This step checks the ignition control circuits and the PCM.