P0131
DTC P0131 HO2S CIRCUIT LOW VOLTAGE (BANK 1/ SENSOR 1)Component Location:
COMPONENT LOCATION
GENERAL DESCRIPTION
The HO2S is used to supply the PCM with information regarding the composition of the air/fuel mixture. The HO2S is positioned in the exhaust pipe ahead of the TWC. To measure the oxygen content, the HO2S requires a supply of ambient air as a reference. The HO2S produces a voltage that varies between 0.1 V and 0.9 V under normal operating conditions. The Powertrain Control Module (PCM) monitors this voltage and determines if the exhaust gas is lean or rich. If the voltage input at the PCM is under approx. 0.45 V the exhaust is lean, and if the voltage input is over approx. 0.45 V the exhaust is rich. The PCM constantly monitors the HO2S signal during closed loop operation and compensates for a rich or lean condition by decreasing or increasing injector pulse width as necessary.
DTC DESCRIPTION
If HO2S signal voltage has continued to be lower than 0.1 V when air-fuel ratio is made to be rich, the PCM determines that a fault exists and a DTC is stored.
DTC Detecting Condition:
Schematic Diagram:
Signal Waveform & Data:
MONITOR SCANTOOL DATA
1. Warm up the engine to normal operating temperature.
2. Connect Scantool then, Ignition "ON" & Engine "ON"
3. Monitor the "HO2S VOLTAGE(B1S1)" parameter on scantool.
Specification:
Verify that the signal is varying from rich(above 0.45 V) to lean(below 0.45 V) a minimum of 3 times in 10 seconds (voltage will vary between 0.1 and 0.9 V).
4. Is the HO2S VOLT. (B1/S1) parameter displayed within specification?
YES: Fault is intermittent caused by poor contact in the sensor's and/or PCM's connector or was repaired and PCM memory was not cleared. Thoroughly check connectors for looseness, poor connection, bending, corrosion, contamination, deterioration, or damage. Repair or replace as necessary and go to "Verification of Vehicle Repair" procedure.
NO: Go to "W/Harness Inspection" procedure.
TERMINAL & CONNECTOR INSPECTION
1. Many malfunctions in the electrical system are caused by poor harness and terminals.
Faults can also be caused by interference from other electrical systems, and mechanical or chemical damage.
2. Thoroughly check connectors for looseness, poor connection, bending, corrosion, contamination, deterioration, or damage.
3. Has a problem been found?
YES: Repair as necessary and go to "Verification of Vehicle Repair" procedure.
NO: Go to "Signal Circuit Inspection " procedure.
SIGNAL CIRCUIT INSPECTION
1. Check for short to ground in harness
1. Ignition "OFF"
2. Disconnect HO(2) sensor connector.
3. Measure resistance between terminal 1 of HO(2) sensor harness connector and chassis ground.
Specification: Infinite
4. Is the measured voltage within specifications?
YES: Go to "Component Inspection" procedure.
NO:
- Check for short to ground in harness.
- Repair or replace as necessary. And then, go to "Verification of Vehicle Repair" procedure.
COMPONENT INSPECTION
1. Visual Inspection of HO2S
1. Visually/physically inspect following items:
- Inspect the front HO2S for Contaminated, deteriorated or aged Front HO2S.
- If contamination is evident on the HO2S, replace contaminated sensor.
2. Is the HO2S visually / physically O.K?
YES: Go to "Check Performance of HO2S" as below.
NO:
- Substitute with a known - good HO2S and check for proper operation.
- If the problem is corrected, replace HO2S and go to "Verification of Vehicle Repair" procedure.
2. Check performance of HO2S
1. Warm-up the engine to normal engine temperature.
2. Connect scantool and Engine "ON"
3. Monitor HO2S voltage(B1/S1) parameter on scantool.
Specification: Verify that the signal is switching from rich(above 0.45 V) to lean(below 0.45 V) a minimum of 3 times in 10 seconds (voltage will vary between 0.1 and 0.9 V).
4. Is the sensor switching properly?
YES: Go to "Check PCM" as below.
NO:
- Substitute with a known - good HO2S and check for proper operation.
- If the problem is corrected, replace HO2S and go to "Verification of Vehicle Repair" procedure.
3. Check PCM
1. Ignition "OFF" & Engine "OFF"
2. Connect Scantool and Ignition "ON"
3. Select simulation function on scantool.
4. Simulate voltage at terminal 1 of HO(2) sensor signal connector.
5. Does the HO(2) sensor signal value changes according to simulation voltage?
YES: Fault is intermittent caused by poor contact in the sensor's and/or PCM's connector. Thoroughly check connectors for looseness, poor connection, bending, corrosion, contamination, deterioration, or damage. Repair or replace as necessary and go to "Verification of Vehicle Repair" procedure.
NO: Substitute with a known - good PCM and check for proper operation.
If the problem is corrected, replace PCM and go to "Verification of Vehicle Repair" procedure.
VERIFICATION OF VEHICLE REPAIR
After a repair, it is essential to verify that the fault has been corrected.
1. Monitor and record the Freeze Frame Data for the Diagnostic Trouble Code(DTC) which has been diagnosed.
2. Using a Scantool, Clear the DTCs.
3. Operate the vehicle within conditions noted in the freeze frame data or enable conditions.
4. Monitor that all readiness tests have been verified as "Complete"
5. Are any DTCs present?
YES: Go to the applicable troubleshooting procedure.
NO: System is performing to specification at this time.