P0134

Circuit Description
The powertrain control module (PCM) supplies a bias voltage Of about 450 mV between the HO2S signal and low circuits. When measured with a 10 megohm digital voltmeter, this may display as low as 350 mV. The oxygen sensor varies the voltage within a range of about 1000 mV when the exhaust is rich, down through about 10 mV when exhaust is lean. The PCM constantly monitors the HO2S signal during closed loop operation and compensates for a rich or lean condition by decreasing or increasing the injector pulse width as necessary. If the HO2S 1 voltage remains at or near the 450 mV bias for an extended period of time, DTC P0134 is set, indicating an open sensor signal or sensor low circuit.

Conditions for Running the DTC
^ None of the following DTCs are present:
- Throttle position (TP) sensor DTCs
- Evaporative emissions (EVAP) DTCs
- Intake air temperature (IAT) sensor DTCs
- Manifold absolute pressure (MAP) sensor DTCs
- Exhaust gas recirculation (EGR) pintle position DTCs
- Engine coolant temperature (ECT) sensor DTCs
- Crankshaft position (CKP) sensor DTCs
- Mass air flow (MAF) sensor DTCs
- Misfire DTCs
- Fuel trim DTCs
- Fuel injector circuit DTCs
^ An engine run time of more than 240 seconds.

Conditions for Setting the DTC
The HO2S 1 signal voltage remains between 400 mV and 500 mV for longer than 30 seconds.

Action Taken When the DTC Sets
^ The PCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has run and failed.
^ The PCM stores the conditions which were present when the DTC set as Freeze Frame and Fail Records data.

Conditions for Clearing the MIL/DTC
^ The PCM turns the MIL off during the third consecutive trip in which the diagnostic has run and passed.
^ The history DTC clears after 40 consecutive warm-up cycles have occurred without a malfunction.
^ The DTC may be cleared by using the scan tool Clear Info function or by disconnecting the PCM battery feed.

Diagnostic Aids
Inspect for the following conditions:
^ A faulty connection or a damaged harness. Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, faulty terminal to wire connections, and any damage to the harness.
^ A malfunctioning HO2S heater or heater circuit. With the ignition on and the engine not running, the HO2S voltage displayed on a scan tool should gradually drop to less than 250 mV or rise to more than 600 mV. If the voltage remains within this range, disconnect the HO2S and connect a test light between the HO2S ignition feed and heater ground circuits. If the test light does not light, repair the open ignition feed or sensor ground circuit as necessary. If the test lamp illuminates and the HO2S signal and low circuits are OK, replace the HO2S.
^ Perform an intermittent test. With the ignition on, monitor the HO2S signal voltage while moving the wiring harness and related connectors. If the malfunction is induced, the HO2S signal voltage changes. This may help isolate the location of the malfunction.

Review the Fail Records vehicle mileage since the diagnostic test last failed to help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table
12. This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.