P0031
DTC P0031 02 SENSOR HEATER CIRCUIT LOW (BANK 1,SENSOR 1)Component Location:
GENERAL DESCRIPTION
In order to control the emission of the CO, HC and NOx components of the exhaust gas, a heated oxygen sensor (HO2S), mounted on the front side and rear side of the catalytic converter, detects the oxygen content in the exhaust gas. The front HO2S signal is used to control air/fuel ratio (closed loop fuel control) and the rear HO2S signal is used to monitor front HO2S and catalyst for proper operation. The HO2S requires a minimum temperature to operate properly and provide a closed loop fuel control system. So the HO2S contains a heater element to reduce warm-up time and ensure proper performance during all driving conditions, which allows for closed loop fuel control or catalyst monitoring immediately upon engine start-up. The ECM controls this heater element by duty cycle. The main relay supplies voltage to the heater and the PCM provides a ground circuit for activating the heater.
DTC DESCRIPTION
PCM sets DTC P0031 if the PCM detects that the front HO2S heater control line is short to ground.
DTC Detecting Condition:
Specification:
Schematic Diagram:
SCHEMATIC DIAGRAM
Signal Waveform & Data:
SIGNAL WAVEFORM & DATA
MONITOR DTC STATUS
This is the inspection procedure to determine whether it is present DTC or memoried one by monitoring the current signal or by using the function of oscilloscope with Hi-scan pro.
1. Connect scantool to Data Link Connector(DLC).
2. Warm up the engine to normal operating temperature.
3. Monitor the "A/F CLOSE LOOP" parameter on the scantool.
NOTE: The data shown above is only for reference and there may be a little difference actually.
4. Is parameter displayed within specifications?
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 then go to "Verification of Vehicle Repair" procedure.
NO: Go to "W/Harness Inspection" procedure
TERMINAL AND 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 "Power Circuit inspection" procedure.
POWER CIRCUIT INSPECTION
1. Ignition "OFF"
2. Disconnect HO2S sensor connector.
3. Ignition "ON" & Engine "OFF"
4. Measure voltage between terminal 4 of sensor harness connector and chassis ground.
Specification: approximately B+
5. Is measure voltage within Specification?
YES: Go to "Control circuit inspection" procedure.
NO:
- Open or short circuit to chassis ground between HO2S harness connector and control relay.
- Repair as necessary and then go to "Verification of Vehicle Repair" procedure.
NOTE: In case, when checking sensor voltage, the output voltage is 0 V
- Possible cause: Blown fuse or open circuit in harness between E/C-J/BOX and terminal 4 of HO2S heater.
CONTROL CIRCUIT INSPECTION
1. Ignition "OFF"
2. Disconnect HO2S sensor connector.
3. Ignition "ON" & Engine "OFF".
4. Measure voltage between terminal 3 of sensor harness connector.
Specification approximately 3.7 V
5. Is measure voltage within Specification?
YES: Go to "Component Inspection" procedure.
NO:
- Check for open or Short to ground in control circuit.
- Repair as necessary and then go to "Verification of Vehicle Repair" procedure.
COMPONENT INSPECTION
1. Check HO2S heater
1. Measure resistance between terminal 3 and 4 of sensor connector(To sensor side)
Specification: 80 °C: 8.0 - 14.0 Ohms
2. Is measure resistance within Specification?
YES: Substitute with a known good PCM and check for proper operation. If the problem is corrected, replace PCM and then go to "Verification of Vehicle Repair" procedure.
NO: Substitute with a known-good HO2S heater and check for proper operation. If the problem is corrected, replace HO2S heater and then 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 rediness test 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.