P0031
DTC P0031 HO2S HEATER CIRCUIT LOW (BANK 1 / SENSOR 1)Component Location:
GENERAL DESCRIPTION
The Engine Coolant Temperature Sensor (ECTS) is located in the engine coolant passage of the cylinder head for detecting the engine coolant temperature. The ECTS uses a thermistor whose resistance changes with the temperature. The electrical resistance of the ECTS decreases as the temperature increases, and increases as the temperature decreases. The reference 5 V in the ECM is supplied to the ECTS via a resistor in the ECM. That is, the resistor in the ECM and the thermistor in the ECTS are connected in series. When the resistance value of the thermistor in the ECTS changes according to the engine coolant temperature, the output voltage also changes. During cold engine operation the ECM increases the fuel injection duration and controls the ignition timing using the information of engine coolant temperature to avoid engine stalling and improve drivability.
DTC DESCRIPTION
If the PCM detects short to ground or open in heater under detecting conditions, PCM sets P0031. MIL (Malfunction Indication Lamp) turns on when the malfunction lasts till consecutive 2 driving cycle.
DTC Detecting Condition:
Specification:
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 DTC STATUS
1. Check DTC Status
1. Connect scantool to Data Link Connector (DLC).
2. IG "ON".
3. Select "Diagnostic Trouble Codes (DTCs)" mode, and then Press F4 (DTAL) to check DTC's information from the DTCs menu
4. Read "DTC Status" parameter.
5. Is parameter displayed "Present fault"?
YES - Go to "Terminal and connector inspection" procedure.
NO - 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.
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 "Component Inspection" procedure.
POWER CIRCUIT INSPECTION
1. IG "OFF" & Disconnect HO2S (B1/S1) connector.
2. IG "ON" & ENG "OFF".
3. Measure resistance between terminal 3 of HO2S (B1/S1) harness connector and chassis ground.
Specification : B+
4. Is the measured voltage within specification ?
YES - Go to "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.
1. IG "OFF" and disconnect HO2S (B1/S1) connector.
2. Measure resistance between terminal 4 of HO2S (B1/S1) harness connector and chassis ground.
Specification : Infinite
3. Is the measured resistance within specification ?
YES - Go to "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
1. IG "OFF" and disconnect HO2S (B1/S1) and PCM connector.
2. Measure resistance between terminal 4 of HO2S (B1/S1) harness connector and terminal 70 of PCM harness connector.
Specification : Approx. below 1 ohm
3. Is the measured resistance within specification ?
YES - Go to "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.
1. IG "OFF" and disconnect HO2S (B1/S1) connector.
2. Measure resistance between terminal 3 and 4 of HO2S (B1/S1) connector (Component Side)
Specification:
3. 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. Connect scan tool and select "Diagnostic Trouble Codes (DTCs)" mode
2. Press F4 (DTAL) and confirm that "DTC Readiness Flag" indicates "Complete". If not, drive the vehicle within conditions noted in the freeze frame data or enable conditions
3. Read "DTC Status" parameter
4. Is parameter displayed "History (Not Present) fault"?
YES - System performing to specification at this time. Clear the DTC
NO - Go to the applicable troubleshooting procedure.