P0134

Code P0134, Heated Oxygen Sensor (HO2S) Circuit (Open Circuit):

Heated Oxygen Sensor (HO2S) Circuit:

CIRCUIT DESCRIPTION
The PCM supplies a voltage of about 0.45 volt (450 mV) between terminals "BF9" and "BF10". (If measured with a 10 megohm digital voltmeter, this may read as low as 0.32 volt.) The Heated Oxygen Sensor (HO2S) varies the voltage within a range of about 1 volt (1000 mV) if the exhaust is rich, down to about 0.10 volt (100 mV) if exhaust is lean.

The sensor is like an open circuit and produces no voltage when it is below about 360°C (600°F). DTC P0131, P0132 or an open sensor circuit or cold sensor causes "Open Loop" operation.

DTC P0134 WILL SET WHEN:
^ Engine coolant temperature above 43°C (110°F).
^ Engine run time more than 40 seconds.
^ HO2S signal voltage is steady between 350 mV and 557 mV.
^ Throttle angle above 3%.
^ All conditions must be met for about 30 seconds.

Action Taken (PCM will default to):
With a current DTC P0134 set, the system will operate in "Open Loop." The MIL (Service Engine Soon) will be illuminated.

TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. If the conditions for DTC P0134 exist, the system will not go into "Closed Loop."
2. This will determine if the sensor or the wiring is the cause of DTC P0134.

DIAGNOSTIC AIDS
An intermittent may be caused by a poor connection, rubbed through wire insulation, or a wire broken inside the insulation. Check for:
^ Poor connection or damaged harness - Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.

^ Faulty HO2S heater or heater circuit - With the ignition "ON," engine "OFF," the HO2S voltage displayed on a Tech 1 should gradually drop to below 0.25 volt, indicating that the heater is working properly. If not, disconnect the HO2S and connect a test light between terminals "C" and "D" If the test light does not light, repair open CKT 1450 or 639. If the test light lights, replace HO2S.

^ Intermittent test - With Tech-1, monitor HO2S signal voltage while moving related connectors and wiring harness, with warm engine running at part throttle in "Closed Loop." If the failure is induced, the HO2S signal voltage reading will change from its normal fluctuating voltage (above 600 mV and below 300 mV) to a fixed value around 450 mV. This may help to isolate the location of the malfunction.