Engine Speed Signal from Ignition Control Module

1-3-1 ENGINE SPEED SIGNAL FROM IGNITION CONTROL MODULE (ICM)

Condition(s) for DTC
^ The ICM transmits speed signals to the MFI module through the knock enrichment and speed circuits simultaneously. The DTC is recorded if an RPM signal is absent in the speed circuit but not in the knock enrichment circuit.

Substitute value
^ None.

Fault source(s)
^ Open-circuit in signal lead.
^ Signal lead short-circuited to ground or supply.
^ Faulty ICM.

Fault symptom(s)
^ Engine cannot be started.
^ Engine stops when running.

TESTING PROCEDURE





Other DTCs
^ Read other DTCs.

If DI DTC 3-2-4 is recorded:
- Proceed to DTC 3-2-4 TESTING PROCEDURE.
If DI DTC 3-2-4 is not recorded:
- Try to start engine.





Engine starting attempt
^ Try to start engine.

If engine starts:
- Proceed to INTERMITTENT FAULT, FAULTY SIGNAL Section below.
If engine does not start:
- Proceed to PERMANENT FAULT, SIGNAL ABSENT Section below.





PERMANENT FAULT, SIGNAL ABSENT

^ Switch ON ignition.
^ Display engine speed signal on Scantool.
^ Operate starter motor and note speed.

If speed rises during start attempt:
- Clean and grease control module connectors.
If speed remains zero during start attempt:
- Proceed to: TESTING BY TROUBLE CODE / IGNITION SYSTEM / DTC 1-3-1 ENGINE SPEED SENSOR SIGNAL.





Cleaning And Greasing Of Control Module connectors
^ Switch OFF ignition.
^ Remove both control modules (MFI and ICM).
^ Check ECM connectors for contact resistance and oxidation.
^ Reinstall both control modules.
^ Try to start engine.

If engine starts:
- DTC is due to poor contact in control module connectors.
If engine does not start:
- Check RPM sensor signal from Ignition Control Module (ICM).





Checking RPM sensor signal from Ignition Control Module (ICM)
^ Switch OFF ignition.
^ Remove both control modules.
^ Connect test box to Ignition system and check ground terminals.
^ Plug ICM into test box adapter.
^ Connect voltmeter across #51 (ICM B21) and #20 (ICM A20) on test box.
^ Operate starter motor.

Instrument should indicate 4 - 7 Volts.

If reading is correct:
- Check speed signal to MFI module.
If instrument indicates approx. 0 Volts:
- Check signal lead.
If instrument indicates battery voltage:
- Check lead between ICM B21 and MFI module B21 for short-circuit to supply.





Checking signal lead
^ Switch OFF ignition.
^ Unplug ICM from test box adapter.
^ Connect ohmmeter between #51 (ICM B21) and #20 (ICM A20) on test box.

Instrument should indicate infinity (no continuity).

If reading is correct:
- Try with new ICM.
It reading is incorrect:
- Check lead between ICM B21 and MFI module B21 for short-circuit to ground.





Checking RPM sensor signal to MFI module
^ Switch OFF ignition.
^ Disconnect test box from Ignition system.
^ Connect test box to MFI system and check ground terminals.
^ Reconnect ICM.





^ Connect voltmeter across #51 (MFI B21) and #20 (MFI A20) on test box.
^ Operate starter motor

Instrument should indicate 4 - 7 Volts.

If reading is correct:
- Try with new ICM.
If reading is incorrect:
- Check lead between ICM B21 and MFI module B21 for open-circuit.

INTERMITTENT FAULT, FAULTY SIGNAL





Checking wiring and connections
^ Check control module connectors for loose connections, and for contact resistance and oxidation.
^ Check lead between ICM B21 and MFI module B21 for intermittent open-circuit, intermittent short-circuit to ground and intermittent short-circuit to supply.