MIL Circuit Troubleshooting

Does the MIL come on and stay on? 

1. 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 ECM (A10) and the data link connector (DLC).
   • An intermittent short in the wire between the ECM (A18) and the gauge assembly.
2. 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 manifold absolute pressure (MAP) sensor.
   • An intermittent short in the wire between the ECM (C28) and throttle position (TP) sensor, vehicle speed sensor (VSS), air pump electric current sensor, or fuel tank pressure (FTP) sensor.
   • Faulty PGM-FI main relay.

Is the low oil pressure indicator on? 

1. YES -  Go to step 3.
2. 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 the No. 5 INSTRUMENT LIGHT BACK UP LIGHT (7.5 A) fuse and the gauge assembly.

Does the engine start? 

1. YES -  Go to step 4.
2. NO -  Go to step  7.

Is the MIL on? 

1. YES -  Substitute a known-good ECM (see HOW TO SUBSTITUTE THE ECM FOR TESTING PURPOSES ) and recheck. If the symptom/indication goes away, replace the original ECM (see ECM REPLACEMENT  ).
2. NO -  Check for an open in the wires between the ECM (A18) and the gauge assembly. Also check for a blown MIL bulb.

Is the fuse OK? 

1. YES -  Go to step 9.
2. 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.

Is the fuse OK? 

1. YES -  Go to step 10.
2. 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.

Fig 2: Checking Continuity Between Body Ground And ECM Connector Terminals C19 And C28

Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there continuity? 

1. YES -  Go to step 12.
2. NO -  Go to step  13.

• Manifold absolute pressure (MAP) sensor
• Vehicle speed sensor (VSS)
• Fuel tank pressure (FTP) sensor
• Throttle position (TP) sensor
• Air pump electrical current sensor

Is there continuity? 

1. 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.
2. NO -  Replace the sensor that made continuity to body ground go away when disconnected.

Fig 3: Measuring Voltage Between Body Ground And ECM Connector Terminals B1 And B9

Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there battery voltage? 

1. YES -  Go to step 16.
2. 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 (see PGM-FI MAIN RELAY CIRCUIT TROUBLESHOOTING ). Repair or replace parts as needed.

Fig 4: Measuring Voltage Between Body Ground And ECM Connector Terminals B2, B10, B20

Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there less than 1.0 V? 

1. YES -  Substitute a known-good ECM (see HOW TO SUBSTITUTE THE ECM FOR TESTING PURPOSES ) and recheck. If the symptom/indication goes away, replace the original ECM (see ECM REPLACEMENT  ).
2. NO -  Repair open in the wire(s) that had more than 1.0 V between G101 and the ECM (B2, B10, B20, B22).

Are any DTCs indicated? 

1. YES -  Go to the indicated DTC's troubleshooting .
2. NO -  Go to step 24.

Fig 5: Checking Continuity Between Body Ground And Data Link Connector (DLC) (16P) Terminal

Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there continuity? 

1. YES -  Repair short in the wire between the DLC and the ECM (A21).
2. NO -  Go to step 27.

Fig 6: Measuring Voltage Between ECM Connector Terminal A10 And Body Ground

Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there about 5 V? 

1. YES -  Go to step 29.
2. NO -  Repair short in the wire between the DLC and the ECM (A10).

Is the MIL on? 

1. YES -  Repair short in the wire between the gauge assembly and the ECM (A18).
2. NO -  Substitute a known-good ECM (see HOW TO SUBSTITUTE THE ECM FOR TESTING PURPOSES ) and recheck. If the symptom/indication goes away, replace the original ECM (see ECM REPLACEMENT  ).