DIAGNOSIS Required Special Tools: • MB991958: Scan Tool (MUT-III Sub Assembly) MB991824: V.C.I MB991827: USB Cable MB991911: Main Harness B • MB991316: Test Harness

STEP 1. Using scan tool MB991958, check data list item 11: Heated Oxygen Sensor Bank 2, Sensor 1 (left front).

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 MB991958 to the data link connector. (2) Start the engine and run at idle. (3) Set scan tool MB991958 to the data reading mode for item 11, Heated Oxygen Sensor Bank 2, Sensor 1 (left front). • Warm up the engine. When the engine is revved, the output voltage should measure 0.6 to 1.0 volt. • Warm up the engine. When the engine is idling, the output voltage should repeat 0.4 volt and 0.6 to 1.0 volt alternately. (4) Turn the ignition switch to the "LOCK" (OFF) position. Q: Is the sensor operating properly? YES: It can be assumed that this malfunction is intermittent. Refer to GROUP 00, How to Use Troubleshooting/Inspection Service Points . NO: Go to Step 2.

STEP 2. Check the left bank heated oxygen sensor (front).

(1) Disconnect the left bank heated oxygen sensor (front) connector A-09 and connect test harness special tool, MB991316, to the connector on the left bank heated oxygen sensor (front) side. (2) Warm up the engine until engine coolant 80°C (176°F) or higher.

(3) Perform a tracing for 5 minutes or more with the engine speed of 4,500 r/min. (4) Connect a digital volt meter between terminal No. 2 (black clip) and terminal No. 4 (white clip). (5) While repeatedly revving the engine, measure the left bank heated oxygen sensor (front) output voltage. Standard value: 0.6 - 1.0 volt • Be very careful when connecting the jumper wire; incorrect connection can damage the oxygen sensor. • Be careful the heater is broken when voltage of beyond 8 volts is applied to the oxygen sensor heater. NOTE: If the sufficiently high temperature (of approximate 400°C or more) is not reached although the oxygen sensor is normal, the output voltage would be possibly low although the rich air-fuel ratio. Therefore, if the output voltage is low, use a jumper wire to connect the terminal No.1 (red clip of special tool) and the terminal No. 3 (blue clip of special tool) of the oxygen sensor with a (+) terminal and (-) terminal of 8 volts power supply respectively, then check again. Q: Is the voltage between 0.6 and 1.0 volt? YES: Go to Step 3. NO: Replace the left bank heated oxygen sensor (front). Then go to Step 5.

STEP 3. Check connector A-09 at left bank heated oxygen sensor (front) and connector C-91 at PCM for damage.

Q: Is the connector in good condition? YES: Go to Step 4. NO: Repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then go to Step 5.

STEP 4. Check for short circuit to ground and harness damage between left bank heated oxygen sensor (front) connector A-09 (terminal No. 4) and PCM connector C-91 (terminal No. 71).

Q: Is the harness wire in good condition? YES: Replace the PCM. Then go to Step 5. NO: Repair it. Then go to Step 5.