DIAGNOSIS Required Special Tools: • MB991958: Scan Tool (MUT-III Sub Assembly) MB991824: V.C.I. MB991827: USB Cable MB991911: Main Harness B • MD998464: Test Harness

STEP 1. Using scan tool MB991958, check data list item 11: Heated Oxygen Sensor (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 (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 - How to Cope with Intermittent Malfunctions . NO: Go to Step 2.

STEP 2. Measure the sensor output voltage at heated oxygen sensor (front) connector B-113 by backprobing.

(1) Do not disconnect connector B-113. (2) Start the engine and run at idle.

(3) Measure the voltage between terminal No. 4 and ground by backprobing. • Warm up the engine. When the engine is 2,500 r/min, the output voltage should repeat 0 to 0.8 volt alternately. (4) Turn the ignition switch to the "LOCK" (OFF) position. Q: Is the measured voltage within the specified range? YES: Go to Step 3. NO: Go to Step 7.

STEP 3. Measure the sensor output voltage at ECM connector C-115 <M/T> or PCM connector C-116 <A/T> by backprobing.

(1) Do not disconnect connector C-115 <M/T> or C-116 <A/T>. (2) Start the engine and run at idle.

(3) Measure the voltage between terminal No. 76 <M/T> or No. 71 <A/T> and ground by backprobing. • Warm up the engine. When the engine is 2,500 r/min, the output voltage should repeat 0 to 0.8 volt alternately. (4) Turn the ignition switch to the "LOCK" (OFF) position. Q: Is the measured voltage within the specified range? YES: Go to Step 4. NO: Go to Step 6.

STEP 4. Check harness connector B-113 at heated oxygen sensor (front) and harness connector C-115 at ECM <M/T> or harness connector C-116 at PCM <A/T> for damage.

Q: Is the harness connector in good condition? YES: Go to Step 5. NO: Repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then go to Step 15.

STEP 5. Using scan tool MB991958, check data list item 11: Heated Oxygen Sensor (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 (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 - How to Cope with Intermittent Malfunctions . NO: Replace the ECM or PCM. Then go to Step 15.

STEP 6. Check harness connector B-113 at heated oxygen sensor (front) and harness connector C-115 at ECM <M/T> or harness connector C-116 at PCM <A/T> for damage.

Q: Is the harness connector in good condition? YES: Repair harness wire between heated oxygen sensor (front) connector B-113 (terminal No. 4) and ECM connector C-115 (terminal No. 76) <M/T> or PCM connector C-116 (terminal No. 71) <A/T> because of open circuit or harness damage. Then go to Step 15. NO: Repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then go to Step 15.

STEP 7. Check harness connector B-113 at heated oxygen sensor (front) for damage.

Q: Is the harness connector in good condition? YES: Go to Step 8. NO: Repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then go to Step 15.

STEP 8. Check for continuity at heated oxygen sensor (front) harness side connector B-113.

(1) Disconnect connector B-113 and measure at the harness side.

(2) Check for the continuity between terminal No. 2 and ground. • Should be less than 2 ohms. Q: Does continuity exist? YES: Go to Step 11. NO: Go to Step 9.

STEP 9. Check harness connector C-115 at ECM <M/T> or harness connector C-118 at PCM <A/T> for damage.

Q: Is the harness connector in good condition? YES: Go to Step 10. NO: Repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then go to Step 15.

STEP 10. Check for open circuit and harness damage between heated oxygen sensor (front) connector B-113 (terminal No. 2) and ECM connector C-115 (terminal No. 92) <M/T> or PCM connector C-118 (terminal No. 57) <A/T>.

Q: Is the harness wire in good condition? YES: Replace the ECM or PCM. Then go to Step 15. NO: Repair it. Then go to Step 15.

STEP 11. Check harness connector C-115 at ECM <M/T> or harness connector C-116 at PCM <A/T> for damage.

Q: Is the harness connector in good condition? YES: Go to Step 12. NO: Repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then go to Step 15.

STEP 12. Check for harness damage between heated oxygen sensor (front) connector B-113 (terminal No. 2) and ECM connector C-115 (terminal No. 92) <M/T> or PCM connector C-118 (terminal No. 57) <A/T>.

Q: Is the harness wire in good condition? YES: Go to Step 13. NO: Repair it. Then go to Step 15.

STEP 13. Check for short circuit to ground and harness damage between heated oxygen sensor (front) connector B-113 (terminal No. 4) and ECM connector C-115 (terminal No. 76) <M/T> or PCM connector C-116 (terminal No. 71) <A/T>.

Q: Is the harness wire in good condition? YES: Go to Step 14. NO: Repair it. Then go to Step 15.

STEP 14. Check the heated oxygen sensor (front).

(1) Disconnect the heated oxygen sensor (front) connector B-113 and connect test harness special tool, MD998464, to the connector on the heated oxygen sensor (front) side. (2) Warm up the engine until engine coolant 80°C (176°F) or higher. (3) Perform a racing for 5 minutes or more with the engine speed of 4,500 r/min.

(4) Connect a digital voltage meter between terminal No. 2 (black clip) and terminal No. 4 (white clip). (5) While repeatedly revving the engine, measure the heated oxygen sensor (front) output voltage. Standard value: 0.6 - 1.0 volt Be very careful when connecting the jumper wires; incorrect connection can damage the heated oxygen sensor (front). Be careful the heater is broken when voltage of beyond 8 volts is applied to the heated oxygen sensor (front) heater. NOTE: If the sufficiently high temperature [of approximate 400°C (752°F) or more] is not reached although the heated oxygen sensor (front) 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) and the terminal No.3 (blue clip) of the heated oxygen sensor (front) with the positive terminal and the negative terminal of 8 volts power supply respectively, then check again. Q: Is the measured voltage between 0.6 and 1.0 volt? YES: Replace the ECM or PCM. Then go to Step 15. NO: Replace the heated oxygen sensor (front). Then go to Step 15.