P0056
DTC P0056 HO2S HEATER CONTROL CIRCUIT (BANK 2 / SENSOR 2)Component Location:
GENERAL DESCRIPTION
The normal operating temperature of the HO2S(Heated Oxygen Sensor) ranges from 350 to 850 °C (662 to 1562 °F). The HO2S heater greatly decreases the amount of time required for fuel control to become active. The ECM provides a pulse width modulated control circuit to adjust current through the heater. When the HO2S is cold, the value of the resistance is tow and the current in the circuit is high. On the contrary, if the temperature in the resistor of the sensor rises, the current drops gradually.
DTC DESCRIPTION
The ECM determines when a rear HO2S heater fault occurs and sets DTC P0056 if measured rear HO2S resistance is lower than the predetermined threshold.
The ECM illuminates the MIL on the second consecutive driving cycle that the diagnostic runs and fails.
DTC Detecting Condition:
Specification:
Schematic Diagram:
Signal Waveform:
MONITOR DTC STATUS
1. Connect scan tool and select "Diagnostic Trouble Codes(DTCs)" mode.
2. Press F4(DTAL) to select DTC information from the DTCs menu.
3. Confirm that "DTC Readiness Flag" indicates "Complete". If not, drive the vehicle within conditions noted in the freeze frame data or enable conditions.
4. Read "DTC Status" parameter.
5. Is parameter displayed "History(Not Present) fault"?
NOTE:
- History (Not Present) fault: DTC occurred but has been cleared.
- Present fault: DTC is occurring at present time.
YES: Fault is intermittent caused by poor contact in the sensor's and/or ECM's connector or was repaired and ECM memory was not cleared. Thoroughly check connectors for loose or poor connection, bending, corrosion, contamination, deterioration, or damage. Repair or replace as necessary and go to "Verification of Vehicle Repair" procedure.
NO: Go to next step as below.
TERMINAL AND CONNECTOR INSPECTION
1. Many malfunctions in the electrical system are caused by poor harness(es) 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 Supply Circuit Inspection" procedure.
POWER SUPPLY CIRCUIT INSPECTION
1. Ignition "OFF".
2. Disconnect HO2S connector.
3. Ignition "ON" & Engine "OFF".
4. Measure voltage between terminal 3 of the HO2S heater harness connector and chassis ground.
Specification : B+
5. Is voltage within the specification?
YES: Go to "Control Circuit Inspection" procedure.
NO:
- Check for an open in the power circuit between the main relay and the HO2S.
- Especially check for "10 A Sensor fuse" is installed and not blown.
- Repair as necessary and go to "Verification of Vehicle Repair" procedure.
CONTROL CIRCUIT INSPECTION
1. Check for open in control harness.
1. Ignition "OFF".
2. Disconnect ECM connectors.
3. Measure resistance between terminals 4 of the HO2S heater harness connector and 19 of the ECM harness connector.
Specification : Approx. 0 ohms
4. Is resistance within the specification?
YES: Go to next step as below.
NO: Repair as necessary and go to "Verification of Vehicle Repair" procedure.
2. Check for short to ground in control circuit
1. Measure resistance between terminal 4 of the HO2S heater harness connector and chassis ground.
Specification : Infinite
2. Is resistance within the specification?
YES: Go to next step as below.
NO: Repair open or short to ground in control circuit and go to "Verification of Vehicle Repair" procedure.
3. Check for short to power in control circuit.
1. Ignition "ON" & Engine "OFF".
2. Measure voltage between terminal 4 of the HO2S heater harness connector and chassis ground.
Specification : Approx. 0 V
3. Is voltage within the specification?
YES: Go to "Component Inspection" procedure.
NO: Repair open or short to ground in control circuit and go to "Verification of Vehicle Repair" procedure.
COMPONENT INSPECTION
1. Measure resistance between terminals 3 and 4 of the sensor connector (Component side).
Specification 3-4 ohms [at 20 - 24 °C (68-75 °F)]
2. Is resistance within the specification?
YES: Check for poor connection between ECM and component: backed out terminal, improper mating, broken locks or poor terminal to wire connection. Repair as necessary and go to "Verification of Vehicle Repair" procedure.
NO: Check HO2S for contamination, deterioration, or damage. Substitute with a known-good HO2S and check for proper operation. If the problem is corrected, replace HO2S 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. Connect scan tool and select "Diagnostic Trouble Codes(DTCs)" mode.
2. Press F4DTAL) 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.