Malfunction Indicator Lamp: Testing and Inspection
MIL Circuit Troubleshooting1. Turn the ignition switch ON (II) and watch the Malfunction Indicator Lamp (MIL).
Does the MIL come on and stay on for more than 20 seconds after turning the ignition switch ON (II)?
YES - If the MIL always come on and stays on, go to step 20. But if the MIL sometimes works normally, first check for these problems.
- An intermittent short in the wire between the PCM (A10) and the Data Link Connector (DLC).
- An intermittent open in the wire between the PCM (A21) and the DLC.
- An intermittent short in the wire between the PCM (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.9 BACK UP LIGHT, INSTRUMENT LIGHT (7.5A) fuse in the driver's under-dash fuse/relay box.
- A loose ACG S (15A) fuse in the under-hood fuse/relay box.
- A loose No.1 FUEL PUMP (15A) fuse in the driver's under-dash fuse/relay box.
- A poor connection at PCM terminal A18.
- An intermittent open in the GRN/ORN wire between the PCM (A18) and the gauge assembly.
- An intermittent short in the wire between the PCM (C19), the manifold absolute pressure (MAP) sensor, and the countershaft speed sensor.
- An intermittent short in the wire between the PCM (C28), the throttle position (TP) sensor, exhaust gas recirculation (EGR) valve position sensor, fuel tank pressure (FTP) sensor, and the mainshaft speed sensor.
2. Turn the ignition switch OFF and then ON (II) again.
Is the low oil pressure indicator light on?
YES - Go to step 3.
NO - Check for these problems.
- A blown No.9 BACK UP LIGHT, INSTRUMENT LIGHT (7.5A) fuse in the driver's under-dash fuse/relay box.
- A short or open in the wire between No.9 BACK UP LIGHT, INSTRUMENT LIGHT (7.5A) 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 PCM connector terminal A18 and body ground with a jumper wire.
6. Turn the ignition switch ON (II).
Is the MIL on?
YES - Substitute a known-good PCM and recheck. If the symptom/indication goes away, replace the original PCM.
NO - Check for an open in the wires between the PCM (A18) and the gauge assembly Also check for a blown MIL bulb.
7. Turn the ignition switch OFF.
8. Inspect the ACG S (15A) fuse in the 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 (15A) fuse and the PGM-FI main relay.
- A short in the wire between the PGM-FI main relay and the PCM, injectors, or IAC valve.
- A blown ACG S (15A) fuse in the driver's under-dash fuse/relay box.
9. Inspect the No.1 FUEL PUMP (15A) fuse in the driver's under-dash fuse/relay box.
Is the fuse OK?
YES - Go to step 10.
NO - Check for these problems.
- A blown the No.1 FUEL PUMP (15A) fuse in the driver's under-dash fuse/relay box.
- A short in the wire between the No.1 FUEL PUMP (15A) fuse and the PGM-FI main relay.
- A short in the wire between the PGM-FI main relay and the fuel pump.
- A faulty PGM-FI main relay or faulty pump.
10. Disconnect PCM connector C (31P).
11. Check for continuity between body ground and PCM 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 PCM connector terminal C19 and C28 individually.
- Manifold Absolute Pressure (MAP) sensor
- Exhaust Gas Recirculation (EGR) valve position sensor
- Fuel Tank Pressure (FTP) sensor
- Throttle Position (TP) sensor
- Mainshaft speed sensor
- Countershaft speed sensor
Is there continuity?
YES - Repair short to body ground in the wire between the PCM (C19) and the MAP sensor or countershaft speed sensor, or the PCM (C28) and the TP sensor, EGR valve position sensor, FTP sensor, or mainshaft speed sensor.
NO - Replace the sensor that made continuity body ground go away when disconnected.
13. Disconnect the injectors and idle air control (IAC) valve connectors.
14. Turn the ignition switch ON (II).
15. Measure voltage between body ground and PCM 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 PCM connector terminals B1 and B9.
- Poor connections at the PGM-FI main relay.
- A faulty PGM-FI main relay. If necessary, repair or replace the faulty part.
16. Turn the ignition switch OFF.
17. Reconnect the connectors to the sensors, then reconnect PCM connector C (31P).
18. Turn the ignition switch ON (II).
19. Measure voltage between body ground and PCM connector terminals B2, B10, B20, and B22 individually.
Is there less than 1.0 V?
YES - Substitute a known-good PCM and recheck. If the symptom/indication goes away, replace the original PCM.
NO - Repair open in the wire(s) that had more than 1.0 V between G101 and the PCM (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.
Does the OBD II scan tool/Honda PGM Tester communicate with the PCM?
YES - Go to step 24.
NO - Go to DLC Circuit Troubleshooting.
24. Check the OBD scan tool/Honda PGM Tester for DTCs.
Are any DTCs indicated?
YES - Go to the DTC Troubleshooting Index. Diagnostic Trouble Code Descriptions
NO - Go to step 26.
25. Turn the ignition switch OFF, then turn it back ON (II).
26. Measure voltage between PCM connector terminal A10 and body ground.
Is there about 5 V (or battery voltage)?
YES - Go to step 27.
NO - Repair short in the wire between the DLC and the PCM (A1O).
27. Turn the ignition switch OFF.
28. Disconnect PCM connector A (32P).
29. Turn the ignition switch ON (II).
Is the MIL on?
YES - Repair short in the wire between the gauge assembly and the PCM (A18).
NO - Substitute a known-good PCM and recheck. If the symptom/indication goes away, replace the original PCM.