P0031
DTC P0031 HO2S HEATER CIRCUIT LOW (BANK 1/ SENSOR 1)Component Location:
COMPONENT LOCATION
GENERAL DESCRIPTION
In order to control emissions of the CO, HC and NOx components of the exhaust gas, heated oxygen sensor (HO2S), mounted on the front side and rear side of 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. The HO2S contains the heater element to reduce its warming-up time and ensure its performance during all driving conditions. The PCM 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
After the Heater is on from Off, the voltage after 5 msec is less than threshold value, the PCM determines that a fault exists and a DTC is stored.
DTC Detecting Condition:
Schematic Diagram:
Signal Waveform:
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 "Power Circuit Inspection" procedure.
POWER SUPPLY CIRCUIT INSPECTION
1. Check Voltage
1. Ignition "OFF"
2. Disconnect HO(2) sensor connector
3. Ignition "ON" & Engine "OFF"
4. Measure voltage between terminal 3 of HO(2) sensor harness connector and chassis ground.
Specification: Approx. B+
5. Is the measured voltage within specification?
YES: Go to "Check for short to ground Heater Control in harness" as below.
NO: Go to "Check for open in harness" as below.
2. Check for open in harness
1. Ignition "OFF"
2. Disconnect HO(2) sensor and Control Relay.
3. Measure resistance between terminal 3 of HO(2) sensor harness connector and terminal 2 of Control Relay harness connector.
Specification: Approx. below 1 Ohms
4. Is the measured resistance within specification?
YES: Go to "Control Circuit Inspection" procedure.
NO:
- Check for open in harness.
- Check that fuse between HO2S and Control Relay is installed or blown off.
- Repair or replace as necessary. And then, go to "Verification of Vehicle Repair" procedure.
CONTROL CIRCUIT INSPECTION
1. Check for short to ground in harness
1. Ignition "OFF"
2. Disconnect HO(2) sensor connector.
3. Measure resistance between terminal 4 of HO(2) sensor harness connector and chassis ground.
Specification: Infinite
4. Is the measured resistance within specification?
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. Check Heater resistance
1. Ignition "OFF"
2. Disconnect HO2S connector
3. Measure resistance between terminals 3 and 4 of the sensor connector(To Component side).
Specification: 3 - 4 Ohms [at 20 °C (68 °F)]
4. Is the measured HO2S heater resistance within specifications?
YES: 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.
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.
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.