P0031
DTC P0031
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
If the HO2S heater output voltage is lower than threshold value for more than 5 seconds while enable condition is met. PCM determines that a fault exists and a DTC is stored. MIL(Malfunction Indication Lamp) turns on when the malfunction lasts till consecutive 2 driving cycle.
DTC Detecting Condition:
DTC DETECTING CONDITION
SPECIFICATION
Heater Resistance (ohms): 8.1 - 11.1 ohms at 21 °C (69.8 °F)
Schematic Diagram:
SCHEMATIC DIAGRAM
Signal Waveform And Data:
SIGNAL WAVEFORM AND DATA
The HO2S requires a minimum temperature to provide a closed loop fuel control system. So the HO2S contains a heater element to reduce its warm-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.
MONITOR SCANTOOL DATA
1. IG "OFF"& connect Scantool.
2. ENG "ON" and warm -up the engine to normal operating temperature.
3. Monitor "HO2S(B1/S1)" status on the service data.
4. Is the "HO2S Heater(B1/S1)" data displayed correctly?
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, ending, corrosion, contamination, deterioration, or damage. Repair or replace as necessary and go to "Verification of Vehicle Repair" procedure
NO - Go to "Terminal and connector 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. IG "OFF"& Disconnect HO2S(B1/S1) connector.
2. IG "ON"& ENG "OFF".
3. Measure voltage between terminal 1 of HO2S(B1/S1) harness connector and chassis ground.
Specification : B+
4. Is the measured voltage within specification?
YES - Go to HO2S(B1/S1) heater "Control Circuit Inspection" procedure.
NO - Repair open or short to ground in HO2S(B1/S1) Heater power circuit then, go to "Verification of Vehicle Repair" procedure.
CONTROL CIRCUIT INSPECTION
1. Check short to ground in harness.
a. IG "OFF" and disconnect HO2S(B1/S1) connector.
b. Measure resistance between terminal 2 of HO2S(B1/S1) harness connector and chassis ground.
Specification : Infinite
c. Is the measured resistance within specification?
YES - Go to HO2S(B1/S1) "Check Open in harness" as follows.
NO - Repair short to ground in HO2S (B1/S1) heater control circuit and go to "Verification of Vehicle Repair" procedure.
2. Check open in harness
a. IG "OFF" and disconnect HO2S(B1/S1) and PCM connector.
b. Measure resistance between terminal 2 of HO2S(B1/S1) harness connector and terminal 70 of PCM harness connector.
Specification : Approx. below 1 Ohm.
c. Is the measured resistance within specification?
YES - Go to HO2S(B1/S1) "Component Inspection" procedure.
NO - Repair open in HO2S(B1/S1) heater control circuit and go to "Verification of Vehicle Repair" procedure.
COMPONENT INSPECTION
1. Check HO2S(B1/S1) Heater resistance.
a. IG "OFF" and disconnect HO2S(B1/S1) connector.
b. Measure resistance between terminal 1 and 2 of HO2S(B1/S1)connector (Component Side)
Specification :
Heater Resistance (ohms): 8.1 - 11.1 ohms at 21 °C (69.8 °F)
c. Is the measured resistance within specification?
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.
NOTE: There is a memory reset function on Scantool that can erase optional parts automatically detected and memorized by PCM.Before or after testing PCM on the vehicle, use this function to reuse the PCM on the others.
NO - Substitute with a known - good HO2S(B1/S1) and check for proper operation. If the problem is corrected, replace HO2S(B1/S1) 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 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.