Federal
Heated Oxygen Sensor (rear) Circuit:
CIRCUIT OPERATION
- A voltage corresponding to the oxygen concentration in the exhaust gas is sent to the PCM (terminal 73) from the output terminal (terminal 1) of the heated oxygen sensor (rear).
- Terminal 2 of the heated oxygen sensor (rear) is grounded with PCM (terminal 57).
TECHNICAL DESCRIPTION
- The output signal of the heated oxygen sensor (front) is counter balanced by the output signal of the heated oxygen sensor (rear).
- The PCM checks for an open circuit in the heated oxygen sensor (rear) output line.
DTC SET CONDITIONS
Check Condition
- Heated oxygen sensor (rear) signal voltage has continued to be 0.15 volt or lower for three minutes or more after starting the engine.
- Engine coolant temperature is higher than 82 °C (180 °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 PCM interface circuit is higher than 4.5 volts when 5 volts is applied to the heated oxygen sensor (rear) output line via a resistor.
- One monitor during one drive cycle
Check Condition
- Heated oxygen sensor (rear) signal voltage remains 0.15 volt or less for at least three minutes after the engine starts.
- Engine coolant temperature is higher than 82 °C (180 °F).
- Engine speed is higher than 1,200 r/min.
- Volumetric efficiency is higher than 25 percent.
- Volume air flow sensor output frequency is 75 Hz or more.
- At least twenty seconds have passed since fuel shut off control was canceled.
- The heated oxygen sensor (front) outputs 0.5 volts or more.
- Monitoring time: 10 seconds
Judgement Criteria
- Making the air/fuel ratio 15 percent for 10 seconds richer does not result in raising the heated oxygen sensor (rear) output voltage beyond 0.15 volt.
- Only one monitor during one drive cycle
Check Condition
- Engine coolant temperature is higher than 82 °C (180 °F).
- Barometric pressure is higher than 76 kPa (11 psi).
- The heated oxygen sensor (front) is active.
- Heated oxygen sensor (rear) output voltage is 0.4 volts or more before fuel shut off commences.
- While fuel is being shut off.
Judgement Criteria
- At least one second has passed before heated oxygen sensor (rear) output voltage falls to 0.40 - 0.15 volts.
or
- At least three seconds have passed before heated oxygen sensor (rear) output voltage falls to 0.15 volts or less.
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.
- PCM failed.
DIAGNOSIS
Required Special Tools:
MB991502: Scan Tool (MUT-II)
MB991658: Test Harness Set
CAUTION: To prevent damage to scan tool MB991502, always turn the ignition switch to "LOCK" (OFF) position before connecting or disconnecting scan tool MB991502.
STEP 1. Using scan tool MB991502, check data list item 59: Heated Oxygen Sensor (rear).
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).
- Warm up the engine. When the engine is revved, the output voltage should repeat 0 volt and 0.6 to 1.0 volt alternately.
If the checks above meet the specification, this malfunction is intermittent. Refer to How to Use Troubleshooting/Inspection Service Points - How to Cope With Intermittent Malfunction.
If the checks above do not meet the specification, go to Step 2.
STEP 2. Check the heated oxygen sensor (rear).
1. Disconnect heated oxygen sensor (rear) connector C-21 and connect test harness special tool, MB991658, to the connector on the heated oxygen sensor (rear) side.
2. Warm up the engine until engine coolant is 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 of the heated oxygen sensor (rear) connector to the positive battery terminal and terminal 4 to the negative battery terminal.
4. Connect a digital voltmeter 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 V
If within specifications, go to Step 3.
If not within specifications, replace the heated oxygen sensor (rear).
Then go to step 7.
STEP 3. Check harness connector C-21 at the heated oxygen sensor (rear) for damage.
If harness connector C-21 is in good condition, go to Step 4.
If harness connector C-21 is damaged, repair or replace it.
Refer to Harness Connector Inspection.
Then go to Step 7.
STEP 4. Check harness connectors C-40, C-41 at the PCM for damage.
If harness connectors C-40, C-41 are in good condition, go to Step 5.
If harness connectors C-40, C-41 are damaged, repair or replace them.
Refer to Harness Connector Inspection.
Then go to Step 7.
STEP 5. Check the harness wire between heated oxygen sensor (rear) connector C-21 and PCM connectors C-40, C-41.
If the wire between heated oxygen sensor (rear) connector C-21 and the PCM connectors C-40, C-41 is not damaged, go to Step 6.
If the wire between heated oxygen sensor (rear) connector C-21 and PCM connectors C-40, C-41 is damaged, repair them. Then go to Step 7.
STEP 6. Replace the heated oxygen sensor (rear).
1. Replace the heated oxygen sensor (rear).
2. Carry out a test drive with the drive cycle pattern. Procedure 4 - Heated Oxygen Sensor Monitor and Procedure 6 - Other Monitor.
3. Check for the diagnostic trouble code (DTC).
If DTC P0136 is not output, the inspection is complete.
If DTC P0136 is output, replace the PCM. Then go to Step 7.
STEP 7. Test the OBD-II drive cycle.
1. Carry out a test drive with the drive cycle pattern. Procedure 4 - Heated Oxygen Sensor Monitor and Procedure 6 - Other Monitor.
2. Read the diagnostic trouble code, and confirm that diagnostic trouble code P0136 does not reset.