P0056

DTC P0036 or P0056 (w/4.8L)

CIRCUIT DESCRIPTION
Heated oxygen sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content in the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. A heating element inside the HO2S minimizes the time required for the sensor to reach operating temperature. Voltage is provided to the heater by the ignition 1 voltage circuit through a fuse. With the engine running, ground is provided to the heater by the HO2S heater low control circuit, through a low side driver within the engine control module (ECM).

The ECM commands the heater ON or OFF to maintain a specific HO2S operating temperature range. The ECM monitors the voltage on the HO2S heater low control circuit for heater fault diagnosis. If the ECM detects that the HO2S heater low control circuit voltage is not within a specified range, DTC P0036 sets for HO2S bank 1 sensor 2, or DTC P0056 sets for HO2S bank 2 sensor 2.

DTC DESCRIPTORS
This diagnostic procedure supports the following DTCs:
- DTC P0036 HO2S Heater Control Circuit Bank 1 Sensor 2
- DTC P0056 HO2S Heater Control Circuit Bank 2 Sensor 2

CONDITIONS FOR RUNNING THE DTC
- The Ignition 1 Signal parameter is between 10-18 volts.
- This diagnostic runs continuously when the above condition is met.

CONDITIONS FOR SETTING THE DTC
The ECM detects that the affected HO2S heater low control circuit is not within a specified range for 6 seconds.

ACTION TAKEN WHEN THE DTC SETS
- The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
- The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
- The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
- A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
- A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
- Clear the MIL and the DTC with a scan tool.

TEST DESCRIPTION

Step 1 - Step 7:

Step 8 - Step 20:

Step 21:

The number below refers to the step number on the diagnostic table.
7. With no fault present, the test lamp will blink once per second.