MIL Does Not Come ON

MIL Circuit Troubleshooting
1. Turn the ignition switch ON (II) and watch the Malfunction Indicator Light (MIL).
Does the MIL come on and stay on?
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 (7.5 A) fuse in the driver's under-dash fuse/ relay box.
- A loose ACG S (15 A) fuse in the under-hood fuse/relay box.
- A loose No.1 FUEL PUMP (15 A) fuse in the driver's under-dash fuse/relay box.
- A poor connection at ECM/PCM terminal A18.
- An intermittent open in the GRN/ORN wire between the ECM/PCM (A18) and the gauge assembly.
- An intermittent short in the wire between the ECM/PCM (C19) and the MAP sensor.
- An intermittent short in the wire between the ECM/PCM (C28) and the TP sensor, EGR valve lift sensor, fuel tank pressure sensor.
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.9 BACK UP LIGHT, INSTRUMENT LIGHT (7.5 A) fuse in the driver's under-dash fusel relay box.
- A short or open in the wire between No.9 BACK UP LIGHT, INSTRUMENT 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 6.




4. Turn the ignition switch OFF and connect ECM/PCM connector terminal A 18 and body ground with a jumper wire.
5. Turn the ignition switch ON (II).
Is the MIL on?
YES-Substitute a known-good ECM/PCM and recheck. If the symptom/indication goes away, replace the original ECM/PCM.
Diagnostic Strategies

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




6. Turn the ignition switch OFF, then disconnect ECM/PCM connector C (31P) and check for continuity between body ground and ECM/PCM connector terminals C19 and C28 individually.
Is there continuity?
YES-Go to step 7.
NO-Go to step 8.
7. Disconnect the 3P connector from each of these sensors, one at a time, and check for continuity between body ground and ECM/PCM connector terminal C19 and C28 individually.
- MAP Sensor
- EGR valve lift sensor
- Fuel tank pressure sensor
- TP sensor
Is there continuity?
YES-Repair the short to body ground in the wire between ECM/PCM (C19) and the MAP sensor, or ECM/PCM (C28) and the TP sensor, EGR valve lift sensor or fuel tank pressure sensor.
NO-Replace the sensor that made continuity to body ground go away when disconnected.
8. Disconnect the fuel injectors and IAC valve connectors.




9. Turn the ignition switch ON (II), and measure voltage between body ground and ECM/PCM connector terminals B1 and B9 individually.
Is there battery voltage?
YES-Go to step 10.
NO-Check for these problems:
- An open in the wire(s) between the PGM-FI main relay and ECM/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 part.
10. Reconnect the connectors to the sensors, then reconnect ECM/PCM connector C (31P).