P0135

Diagnostic Chart (Part 1 Of 2):

Diagnostic Chart (Part 2 Of 2):

Engine Controls Schematics: HO2S #1 and HO2S #2:

CIRCUIT DESCRIPTION
Heated Oxygen Sensors (HO2S) are used to minimize the amount of time required for closed loop fuel control operation and to allow accurate catalyst monitoring. The oxygen sensor heater greatly decreases the amount of time required for fuel control sensor HO2S 1 to become active. The oxygen sensor heater is required by catalyst monitor sensor HO2S 2 to maintain a sufficiently high temperature. This allows accurate exhaust oxygen content readings further from the engine.

The PCM will run the heater test only after a cold start (determined by engine coolant and intake air temperature at the time of start-up) and only once during an ignition cycle. When the engine is started the PCM will monitor the HO2S voltage. When the HO2S voltage indicates a sufficiently active sensor, the PCM looks at how much time has elapsed since start-up. If the PCM determines that too much time was required for the HO2S 1 to become active, a DTC P0135 will set. The time it should take the HO2S to reach operating temperature is based on the engine coolant temperature at start up and the average mass air flow since start-up (higher average airflow or higher start-up engine coolant temperature shorter time to HO2S activity).

CONDITIONS FOR RUNNING THE DTC
^ No active TP, MAP, MAF, ECT, IAT sensor, fuel injector circuit, EVAP, AIR, DTCs present.
^ Intake Air Temperature (IAT) is less than 35°C (95°F) at start up.
^ Engine Coolant Temperature (ECT) is less than 35°C (95°F) at start up.
^ IAT and ECT are within 6°C (42°F) of each other at start up.
^ System voltage between 9.0 and 18.0 volts.
^ AIR pump commanded OFF.

CONDITIONS FOR SETTING THE DTC
HO2S 1 voltage remains within 150 mV of the bias voltage (about 450 mV) for a longer amount of time than it should. The amount of time varies depending on engine coolant temperature at start-up and average air flow since start-up, but will not exceed 2.5 minutes.

ACTION TAKEN WHEN THE DTC SETS
^ The PCM will illuminate the Malfunction Indicator Lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.
^ The PCM will store conditions which were present when the DTC set as Freeze Frame and Failure Records data.
^ If the misfire is determined to be catalyst damaging, the PCM will flash the MIL.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The PCM will turn OFF the MIL during the third consecutive trip in which the diagnostic has been run and passed.
^ The History DTC will clear after 40 consecutive warm-up cycle have occurred without a malfunction.
^ The DTC can be cleared by using a scan tool.

DIAGNOSTIC AIDS
Inspect for the following conditions:

IMPORTANT: Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.

^ Poor terminal connection.
Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Use a corresponding mating terminal to test for proper tension. Refer to Diagrams for diagnosis and repair.
^ Damaged harness.
Inspect the wiring harness for damage. If the harness inspection does not reveal a problem, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the scan tool display may indicate the location of the fault. Refer to Diagrams for diagnosis and repair.
^ Inspect the PCM and the engine grounds for clean and secure connections.

If the DTC is determined to be intermittent, reviewing the Failure Records can be useful in determining when the DTC was last set.

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table:
2. The HO2S should be allowed to cool before performing this test. If the HO2S heater is functioning, the signal voltage will gradually increase or decrease as the sensor element warms. If the heater is not functioning, the HO2S signal will remain near the 450 mv bias voltage.
4. This step ensures that the ignition feed circuit to the HO2S is not open or shorted. The test lamp should be connected to a good ground, in case the HO2S low or HO2S heater ground circuit is faulty.
5. This step tests the HO2S heater ground circuit.
6. This step inspects for an open or shorted HO2S heater element. The heater element resistance will vary according to HO2S temperature (a hot HO2S healer element will measure a much higher resistance than a HO2S heater element at room temperature). It is important to allow the HO2S to cool before measuring HO2S heater element resistance.