DIAGNOSIS Required Special Tools: • MB991958: Scan Tool (MUT-III Sub Assembly) MB991824: V.C.I MB991827: USB Cable MB991911: Main Harness B

STEP 1. Using scan tool MB991958, read the diagnostic trouble code (DTC).

To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958. (1) Connect scan tool MB99958 to the data link connector. (2) Turn the ignition switch to the "ON" position. (3) Erase the DTC. (4) Start the engine and run it at idle. (5) Read the DTC. (6) Turn the ignition switch to the "LOCK" (OFF) position. Q: Is DTC P1603 set? YES: Go to Step 2. NO: The procedure is complete.

STEP 2. Measure the backup power supply voltage at PCM connector C-90 by backprobing.

(1) Do not disconnect the PCM connector C-90.

(2) Measure the voltage between terminal No. 66 and ground by backprobing. • Voltage should be battery positive voltage. Q: Is battery positive voltage (approximately 12 volts) present? YES: Go to Step 5. NO: Go to Step 3.

STEP 3. Measure the backup power supply voltage at PCM harness side connector C-90.

(1) Disconnect the PCM connector C-90 and measure at the harness side.

(2) Measure the voltage between terminal No. 66 and ground. • Voltage should be battery positive voltage. Q: Is battery positive voltage (approximately 12 volts) present? YES: Go to Step 4. NO: Repair harness wire between battery and PCM connector C-90 (terminal No. 66) because of open circuit or short circuit to ground. Then go to Step 6.

STEP 4. Check connector C-90 at PCM for damage.

Q: Is the harness connector in good condition? YES: Repair harness wire between battery and PCM connector C-90 (terminal No. 66) because of harness damage. Then go to Step 6. NO: Repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then go to Step 6.

STEP 5. Check connector C-90 at PCM for damage.

Q: Is the harness connector in good condition? YES: Replace the PCM. Then go to Step 6. NO: Repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then go to Step 6.