MIL Circuit Troubleshooting

1. Turn the ignition switch ON (II), and watch the Malfunction Indicator Lamp (MIL).

Does the MIL come on and stay on?

YES - If the MIL always come on and stays on, go to step 21. But if the MIL sometimes works normally, first check for these problems.
- An intermittent short in the wire between the ECM (A10) and the data link connector (DLC).
- An intermittent short in the wire between the ECM (A18) and the gauge assembly.

NO - If the MIL is always off, go to step 2. But if the MIL sometimes works normally, first check for these problems.
- A loose No.5 INSTRUMENT LIGHT BACK UP LIGHT (7.5 A) fuse in the under-dash fuse/relay box.
- A loose ACG S (15 A) fuse in the under-hood fuse/relay box.
- A loose No.2 FUEL PUMP SRS (15 A) fuse in the under-dash fuse/relay box.
- A poor connection at ECM terminal A18.
- An intermittent open in the GRN/ORN wire between the ECM (A18) and the gauge assembly.
- An intermittent short in the wire between the ECM (C19) and the MAP sensor.
- An intermittent short in the wire between the ECM (C28) and TP sensor, vehicle speed sensor (VSS), air pump electric current sensor, or fuel tank pressure (FTP) sensor.
- PGM-FI main relay.

2. Turn the ignition switch OFF and then ON (II) again.

Is the low oil pressure light on?

YES - Go to step 3.

NO - Check for these problems.
- A blown No.5 INSTRUMENT LIGHT BACK UP LIGHT (7.5 A) fuse in the under-dash fuse/relay box.
- A short or open in the wire between No.5 INSTRUMENT LIGHT BACK UP LIGHT (7.5 A) fuse and the gauge assembly.

3. Try to start the engine.

Does the engine start?

YES - Go to step 4.

NO - Go to step 7.

4. Turn the ignition switch OFF.




5. Connect ECM connector terminal A18 to body ground with a jumper wire.
6. Turn the ignition switch ON (II).

Is the MIL on?

YES - Substitute a known-good ECM and recheck. If the symptom/indication goes away, replace the original ECM.

NO - Check for an open in the wires between the ECM (A18) and the gauge assembly. Also check for a blown MIL bulb.

7. Turn the ignition switch OFF.
8. Inspect the ACG S (15 A) fuse in the main under-hood fuse/relay box.

Is the fuse OK?

YES - Go to step 9.

NO - Check for these problems.
- A short in the wire between the ACG S (15 A) fuse and the PGM-FI main relay.
- A short in the wire between the PGM-FI main relay and the ECM, injectors, or IAC valve.

9. Inspect the No.2 FUEL PUMP SRS (15 A) fuse in the under-dash fuse/relay box.

Is the fuse OK?

YES - Go to step 10.

NO - Check for these problems.
- A short in the wire between the No.2 FUEL PUMP SRS (15 A) fuse and the PGM-FI main relay or the SRS unit.
- A short in the wire between the PGM-FI main relay and the fuel pump.
- A faulty PGM-FI main relay or faulty fuel pump.

10. Disconnect ECM connector C (31P).




11. Check for continuity between body ground and ECM connector terminals C19 and C28 individually.

Is there continuity?

YES - Go to step 12.

NO - Go to step 13.

12. Disconnect the 3P connector from each of these sensors, one at a time, and check for continuity between body ground and ECM connector terminal C19 and C28 individually.
- MAP sensor
- Vehicle speed sensor (VSS)
- Fuel tank pressure (FTP) sensor
- TP sensor
- Air pump electrical current sensor

Is there continuity?

YES - Repair short to body ground in the wire between the ECM (C19) and the MAP sensor, or the ECM (C28) and the TP sensor, VSS, FTP sensor or air pump electrical current sensor.

NO - Replace the sensor that made continuity to body ground go away when disconnected.

13. Disconnect the injectors and IAC valve connectors.
14. Turn the ignition switch ON (II).




15. Measure voltage between body ground and ECM connector terminals B1 and B9 individually.

Is there battery voltage?

YES - Go to step 16.

NO - Check for these problems:
- An open in the wire(s) between the PGM-FI main relay and ECM connector terminals B1 and B9.
- Poor connections at the PGM-FI main relay.
- A faulty PGM-FI main relay. Repair or replace parts as needed.

16. Turn the ignition switch OFF.
17. Reconnect the connectors to the sensors, then reconnect ECM connector C (31P)
18. Turn the ignition switch ON (II).




19. Measure voltage between body ground and ECM connector terminals B2, B10, B20, and B22 individually.

Is there less than 1.0 V?

YES - Substitute a known-good ECM and recheck. If the symptom/indication goes away, replace the original ECM.

NO - Repair open in the wire(s) that had more than 1.0 V between G101 and the ECM (B2, B10, B20, B22).

20. Turn the ignition switch OFF.
21. Connect an OBD II scan tool/Honda PGM Tester.
22. Turn the ignition switch ON (II).
23. Read the OBD II scan tool/Honda PGM Tester.

Are any DTCs indicated?

YES - Go to the DTC Troubleshooting Index.

NO - Go to step 24.

24. Turn the ignition switch OFF.
25. Disconnect ECM connector A (32P).




26. Check for continuity between body ground and Data Link Connector (DLC) (16P) terminal No.15.

Is there continuity?

YES - Repair short in the wire between the DLC and the ECM (A21).

NO - Go to step 27.

27. Turn the ignition switch ON (II).




28. Measure voltage between ECM connector terminal A10 and body ground.

Is there about 5 V?

YES - Go to step 29.

NO - Repair short in the wire between the DLC and the ECM (A10).

29. Turn the ignition switch OFF.
30. Disconnect ECM connector A (32P).
31. Reconnect the negative cable to the battery.
32. Turn the ignition switch ON (II).

Is the MIL on?

YES - Repair short in the wire between the gauge assembly and the ECM (A18).

NO - Substitute a known-good ECM and recheck. If the symptom/indication goes away, replace the original ECM.