P0134

DTC P0134

CIRCUIT DESCRIPTION
The heated oxygen sensors (HO2S) are used for fuel control and catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the engine is started, the control module operates in an Open Loop mode, ignoring the HO2S signal voltage while calculating the air-to-fuel ratio. The control module supplies the HO2S with a reference, or bias voltage of approximately 450 mV. While the engine runs, the HO2S heats up and begins to generate a voltage within a range of 0-1,000 mV. This voltage will fluctuate above and below the bias voltage. Once sufficient HO2S voltage fluctuation is observed by the control module, Closed Loop is entered. The control module uses the HO2S voltage to determine the air-to-fuel ratio. An HO2S voltage that increases above bias voltage toward 1,000 mV indicates a rich fuel mixture. An HO2S voltage that decreases below bias voltage toward 0 mV indicates a lean fuel mixture.

The heating elements inside each HO2S heat the sensor to bring the sensor up to operating conditions faster. This allows the system to enter Closed Loop earlier and the control module to calculate the air-to-fuel ratio sooner.

The HO2S utilizes the following circuits:
- A signal circuit
- A low reference circuit
- An ignition 1 voltage circuit
- A heater control circuit

If the ECM detects that the HO2S voltage remains within the bias voltage range, DTC P0134 will set.

DTC DESCRIPTOR
This diagnostic procedure supports the following DTC:
DTC P0134 HO2S Circuit Insufficient Activity Sensor 1

CONDITIONS FOR RUNNING THE DTC
- DTCs P0106, P0107, P0108, P0117, P0118, P0122, P0123, P0171, P0172, P0201-P0204, P0300, P0336, P0337, P0351, P0352, P0401, P0402, P0404, P0405, P0406, P0441, P0443, P0488, P0502, P0506, and P0507 are not set.
- The engine coolant temperature is more than 60°C (140°F).
- The ignition 1 voltage is more than 10 volts.
- The fuel system is in closed loop.
- The calculated airflow is more than 9 g/s.
- The engine run time is more than 60 seconds.
- DTC P0134 runs continuously once the above conditions are met for 2 seconds.

CONDITIONS FOR SETTING THE DTC
The ECM detects that the HO2S 1 voltage is between 300-600 mV for 10 seconds.

ACTION TAKEN WHEN THE DTC SETS
- The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
- The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/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

Steps 1-3:

Steps 4-6:

Steps 7-9:

Steps 10-14:

The numbers below refer to the step numbers on the diagnostic table.
4. This step tests for a short to voltage to the signal circuit of the HO2S 1.
5. This step tests the HO2S 1 signal and the low reference circuit for an open. The HO2S voltage should go low.