Inspection Procedure 1

Communication with Scan Tool MB991502 is Impossible.

Immobilizer-ECU Power Supply, Ground And ECM <M/T> Or PCM <A/T> Communication Line Circuit:

Connectors:

Communication with scan tool MB991502 is impossible
Immobilizer-ECU is energized when the ignition switch is turned "ON," and the MFI relay is turned on. The ECM or PCM transmits a signal from scan tool MB991502 to the immobilizer-ECU as it is. In the same way, a signal from the immobilizer ECU is also transmitted to scan tool MB991502 as it is.

TECHNICAL DESCRIPTION (COMMENT)
- This malfunction may be caused by a defective immobilizer-ECU, ECM or PCM , or a defect in the communication line between the immobilizer-ECU and ECM or PCM . If this malfunction appears when the MFI system and scan tool MB991502 can communicate each other, MFI system DTC P1610 will reset.
- If the MFI system is normal, the MFI relay can be determined as normal. In addition, if the MFI system and scan tool MB991502 can communicate each other, the circuits between the data link connector and the ECM or PCM can determined as normal.

NOTE: If this malfunction appears, MFI system DTC P1610 will be output

TROUBLESHOOTING HINTS
- Malfunction of immobilizer-ECU
- Malfunction of ECM or PCM
- Damaged harness wires or connectors

DIAGNOSIS

Required Special Tools:
- MB991223: Harness Set
- MB991502: Scan Tool (MUT-II)

STEP 1. Check scan tool MB991502 communicates with the MFI system and MFI system DTC output other than P1610.

Q: Can scan tool MB991502 communicate with the MFI system? Does MFI system DTC other than P1610 reset?

YES: Go to step 2.

NO: Refer to Computers and Control Systems/Testing, Diagnosis.

STEP 2. Check the immobilizer-ECU power supply circuit by backprobing.
1. Do not disconnect immobilizer-ECU connector C-79.
2. Turn the ignition switch to the "ON" position.
3. Measure the voltage between terminal 7 and ground by backprobing.

Q: Is the voltage approximately 12 volts (battery positive voltage)?

YES: Go to step 5.

NO: Go To Step 3.

STEP 3. Check immobilizer-ECU connector C-79 and MFI relay connector A-18X for damage.

Q: Are immobilizer-ECU connector C-79 and MFI relay connector A-18X damaged?

YES: Repair or replace them. Refer to Harness Connector Inspection. Confirm that scan tool MB991502 communicates normally.

NO: Go To Step 4.

STEP 4. Check the harness wires between immobilizer-ECU connector C-79 and MFI relay connector A-18X.

NOTE: After checking intermediate connector C-28, check the wires. If intermediate connector C-28 is damaged, repair or replace it. Refer to Harness Connector Inspection.

Q: Are the harness wires between immobilizer-ECU connector C-79 and MFI relay connector A-18X damaged?

YES: Replace them. Confirm that scan tool MB991502 communicates normally.

NO: There is no action to be taken.

STEP 5. Check the immobilizer-ECU ground circuit by back probing.
1. Do not disconnect immobilizer-ECU connector C-79.
2. Measure the resistance between terminal 3 and ground by backprobing.

Q: Is the resistance less than two ohm?

YES: Go to Step 7.

NO: Go to Step 8.

STEP 6. Check immobilizer-ECU connector C-79 for damage.

Q: Is immobilizer-ECU connector C-79 in good condition?

YES: Go to step 7.

NO: Repair or replace it. Refer to Harness Connector Inspection. Confirm that scan tool MB991502 communicates normally.

STEP 7. Check the harness wire between immobilizer-ECU connector C-79 and ground.

Q: Is the harness wire between immobilizer-ECU connector C-79 and ground damaged?

YES: Repair it. Confirm that scan tool MB991502 communicates normally.

NO: There is no action to be taken.

STEP 8. Check the harness wires between immobilizer-ECU connector C-79 and ECM connector C-56 <2.4L M/T>, C-62 <3.0L M/T> or PCM connector C-61 <2.4L A/T>, C-63 <3.0L A/T>.

Q: Are the harness wires between immobilizer-ECU connector C-79 and ECM connector C-56 <2.4L M/T>, C-62 <3.0L M/T> or PCM connector C-41 <2.4L A/T>, C-63 <3.0L A/T> damaged?

YES: Repair them. Confirm that scan tool MB991502 communicates normally.

NO: Go to Step 9.

STEP 9. Replace the immobilizer-ECU or ECM or PCM .
Replace the immobilizer-ECU or ECM or PCM .

Q: Did the communication with MUT-II become possible after replacing the immobilizer-ECU or the power train control module?

YES: Register the password (secret code) and encrypted code. Confirm that scan tool MB991502 communicates normally.

NO: Go To Step 10.

STEP 10. Recheck for malfunction

Q: Is a malfunction eliminated?

YES: This diagnosis is complete. (If no malfunction are not found in all steps, an intermittent malfunction is suspected. Refer to How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction.)

NO: Replace the immobilizer-ECU or ECM or PCM .