P1134

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 of the exhaust stream. When the vehicle is first started, the powertrain control module (PCM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air-to-fuel ratio. The PCM supplies the HO2S with a reference, or bias, voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1,000 mV that fluctuates above and below bias voltage once in Closed Loop. A high HO2S voltage output indicates a rich fuel mixture. A low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and to provide an accurate voltage signal. The PCM calculates a transition time ratio for rich-to-lean and lean-to-rich HO2S voltage switches. If the PCM detects that the calculated transition time ratio is incorrect, DTC P1134 will set.

Each HO2S 1 has the following circuits:
- HO2S 1 high signal
- HO2S 1 low reference
- HO2S 1 heater ignition voltage
- HO2S 1 heater low control
- Low reference loop

CONDITIONS FOR RUNNING THE DTC
- DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0201, P0202, P0203, P0204, P0205, P0206, P0410, P0440, P0442, P0443, P0446, P0449, P1441 are not set.
- The vehicle is not in Park or Neutral.
- The Engine Run Time parameter is at least 60 seconds.
- The Loop Status parameter is closed.
- The MAF sensor parameter is between 13-30 g/s.
- The Engine Speed parameter is between 1,300-3,000 RPM.
- The ECT Sensor parameter is more than 70°C (158°F).
- The system voltage is between 9-18 volts.

CONDITIONS FOR SETTING THE DTC
The PCM detects that the average transition time ratio is not within 0.4-4.2 during a 100 second monitoring period.

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

Steps 1-4:

Steps 5-8:

Step 9:

Steps 10-15:

The numbers below refer to the step numbers on the diagnostic table.
2. A normally functioning HO2S 1 voltage signal will fluctuate above and below the bias voltage amount.
4. A voltage reading other than the specified amount in this step indicates an open circuit condition in the high signal circuit or the PCM.
6. This step tests the HO2S 1 signal circuits from the HO2S connector and the PCM connectors, including the low reference loop between the PCM connectors.
8. This step tests for correct HO2S 1 heater circuit operation up to the HO2S connector. The heater low control is controlled by the PCM. The engine must be running to enable the HO2S heater.
9. The conditions listed in the table may contribute to the failure of the HO2S. The conditions listed apply only to this type of failure.