P0138
Heated Oxygen Sensor (rear) Circuit:
Connectors:
CIRCUIT OPERATION
A voltage corresponding to the oxygen concentration in the exhaust gas is sent to the ECM (terminal 75)
- Terminal 2 of the heated oxygen sensor (rear) is grounded with ECM (terminal 92)
TECHNICAL DESCRIPTION
- The output signal of the heated oxygen sensor (front) is compensated by the output signal of the heated oxygen sensor (rear).
- The ECM
DTC SET CONDITIONS
Check Conditions
- 3 minutes or more have passed since the starting sequence was completed.
- Heated oxygen sensor (rear) signal voltage has continued to be 0.15 volt or lower
- Engine coolant temperature is higher than 76 °C (169 °F).
- Engine speed is higher than 1,200 r/min.
- Volumetric efficiency is higher than 25 percent.
- Monitoring time: 7 seconds.
Judgment Criteria
- Input voltage supplied to the ECM
- Only one monitor during one drive cycle.
TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
- Heated oxygen sensor (rear) failed.
- Open circuit in heated oxygen sensor (rear) output line.
- Open circuit in heated oxygen sensor (rear) ground line.
- ECM failed.
- PCM failed.
DIAGNOSIS
Required Special Tools
- MB991502: Scan Tool (MUT-II)
- MB991223: Test Harness Set
STEP 1. Using scan tool MB991502, check data list item 59: Heated Oxygen Sensor (rear).
CAUTION: To prevent damage to scan tool MB991502, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991502.
1. Connect scan tool MB991502 to the data link connector.
2. Start the engine and run at idle.
3. Set scan tool MB991502 to the data reading mode for item 59, Heated Oxygen Sensor (rear).
- Warming up the engine. When the engine is revved, the output voltage should repeat 0 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 How to Use Troubleshooting/Inspection Service Points.
NO: Go to Step 2.
STEP 2. Check the sensor output voltage at heated oxygen sensor (rear) connector C-11 by backprobing.
1. Do not disconnect the connector C-11.
2. Start the engine and run at idle.
3. Measure the voltage between terminal 1 and ground by backprobing.
- Warming up the engine. When the engine is revved, the output voltage should repeat 0 volt and 0.6 to 1.0 volt alternately.
4. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the voltage normal?
YES: Go to Step 3.
NO: Go to Step 7.
STEP 3. Check the sensor output voltage at ECM connector C-115
1. Do not disconnect the connector C-115
2. Start the engine and run at idle.
3. Measure the voltage between terminal 75
- Warming up the engine. When the engine is 2,500 r/min, the output voltage should repeat 0 volt and 0.6 to 1.0 volt alternately.
4. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the voltage normal?
YES: Go to Step 4.
NO: Go to Step 6.
STEP 4. Check connector C-11 at heated oxygen sensor (rear) and connector C-115 at ECM
Q: Is the connector in good condition?
YES: Go to Step 5.
NO: Repair or replace it. Refer to Harness Connector Inspection. Then go to Step 14.
STEP 5. Using scan tool MB991502, check data list item 59: Heated Oxygen Sensor (rear).
CAUTION: To prevent damage to scan tool MB991502, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991502.
1. Connect scan tool MB991502 to the data link connector.
2. Start the engine and run at idle.
3. Set scan tool MB991502 to the data reading mode for item 59, Heated Oxygen Sensor (rear).
- Warming up the engine. When the engine is revved, the output voltage should repeat 0 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 How to Use Troubleshooting/Inspection Service Points.
NO: Replace the ECM or PCM. Then go to Step 14.
STEP 6. Check connector C-11 at heated oxygen sensor (rear) and connector C-115 at ECM
Q: Is the connector in good condition?
YES: Repair harness wire between heated oxygen sensor (rear) connector C-11 terminal 1 and ECM connector C-115 terminal 75
NO: Repair or replace it. Refer to Harness Connector Inspection. Then go to Step 14.
STEP 7. Check connector C-11 at heated oxygen sensor (rear) for damage.
Q: Is the connector in good condition?
YES: Go to Step 5.
NO: Repair or replace it. Refer to Harness Connector Inspection. Then go to Step 14.
STEP 8. Check the continuity at heated oxygen sensor (rear) harness side connector C-11.
1. Disconnect the connector C-11 and measure at the harness side.
2. Check for the continuity between terminal 2 and ground.
- Should be less than 2 ohm.
Q: Is the continuity normal?
YES: Go to Step 11.
NO: Go to Step 9.
STEP 9. Check connector C-115 at ECM
Q: Is the connector in good condition?
YES: Go to Step 10.
NO: Repair or replace it. Refer to Harness Connector Inspection. Then go to Step 14.
STEP 10. Check for open circuit and harness damage between heated oxygen sensor (rear) connector C-11 terminal 2 and ECM connector C-115 terminal 92
Q: Is the harness wire in good condition?
YES: Replace the ECM or PCM. Then go to Step 14.
NO: Repair it. Then go to Step 14.
STEP 11. Check connector C-115 at ECM
Q: Is the connector in good condition?
YES: Go to Step 12.
NO: Repair or replace it. Refer to Harness Connector Inspection. Then go to Step 14.
STEP 12. Check for harness damage between heated oxygen sensor (rear) connector C-11 terminal 2 and ECM connector C-115 terminal 92
Q: Is the harness wire in good condition?
YES: Go to Step 13.
NO: Repair it. Then go to Step 14.
STEP 13. Check the heated oxygen sensor (rear).
1. Disconnect the heated oxygen sensor (rear) connector C-11 and connect test harness special tool, MB991223, to the connector on the heated oxygen sensor (front) side.
2. Warm up the engine until engine coolant 80 °C (176 °F) or higher.
CAUTION: Be very careful when connecting the jumper wires; incorrect connection can damage the heated oxygen sensor (rear).
3. Use the jumper wires to connect terminal 3 to the positive battery terminal and terminal 4 to the negative battery terminal
4. Connect a digital volt meter between terminal 1 and terminal 2.
5. While repeatedly revving the engine, measure the heated oxygen sensor (rear) output voltage.
Standard value: 0.6 - 1.0 volt
Q: Is the voltage at the standard value?
YES: Replace the ECM or PCM. Then go to Step 14.
NO: Replace the heated oxygen sensor (rear). Then go to Step 14.
STEP 14. Test the OBD-II drive cycle.
1. Carry out a test drive with the drive cycle pattern. Refer to, Procedure 6 - Other Monitor.
2. Check the diagnostic trouble code (DTC).
Q: Is the DTC P0138 output?
YES: Retry the troubleshooting.
NO: The inspection is complete.