P0135

Diagnostic Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION

IMPORTANT: if the voltage is measured with a 10 Megaohm Digital Voltmeter, the voltage may read as low as 0.32 volt (320 mV).

The VCM supplies a voltage of approximately 0.45 volt (450 mV) between the HO2S High and HO2S Low circuits. The Heated Oxygen Sensor (HO2S) varies the voltage from approximately 1.0 volt (1000 mV) during rich conditions to 0.10 volt (100 mV) during lean conditions.

When the HO2S temperature measures below 360°C (600°F) the sensor will not produce any voltage and will behave like an open circuit. This will result in an Open Loop operation.

The HO2S heater provides for a faster sensor warm-up which allows the sensor to become active in a shorter period of time. The sensor will remain active during a long extended idle. The DTC P0135 determines if the HO2S is functioning properly by checking the response time of the sensor.

CONDITIONS FOR SETTING THE DTC

The following conditions will set this DTC:

^ The system voltage is greater than 9.0 volts but less than 17.0 volts,( if voltage remains outside this window for 4 consecutive seconds, the test is void for this cold start.)

^ The MAF is less than 27 grams

^ The engine run time is greater than 2 seconds

^ The ECT sensor is less than 32°C

^ The IAT is less than 32°C

^ The difference between the ECT and IAT is no more than 5°C

^ The elapsed time is excessive to obtain 0.300-0.600 volts from the HO2S bias voltage

^ An excessive amount of time for the HO2S to become active after startup

ACTION TAKEN WHEN THE DTC SETS

The VCM turns the MIL ON after 2 consecutive test failures.

CONDITIONS FOR CLEARING THE MIL/DTC

^ The VCM turns the MIL OFF after 3 consecutive drive trips when the test has Run and Passed and not Failed.

^ A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant temperature exceeds 70°C (160°F) during the same ignition cycle).

^ Use the scan tool Clear Information function.

^ Disconnect the VCM battery feed for 30 seconds.

DIAGNOSTIC AIDS

IMPORTANT: Never solder the HO2S wires. For pr9per wire and connection repairs, refer to Wiring Repairs in Engine Electrical.

^ Check for a poor connection or a damaged harness.

^ Inspect the harness for the following conditions:

- Backed out terminals

- Improper mating

- Broken locks

- Improperly formed or damaged terminals

- A poor terminal to wire connection

- A damaged harness

TEST DESCRIPTION

The number(s) below refer to the step number(s) 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 450mv bias voltage,

4. This step determines if the ignition feed circuit to the HO2S is not open or shorted. The test light should be connected to a known good chassis ground, in case the HO2S low or HO2S heater ground circuit is faulty.

5. This step checks the HO2S heater ground circuit.

6. This step checks for an open or shorted HO2S heater element. The heater element resistance will vary according to HO2S temperature (a hot HO2S heater 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 the HO2S heater element resistance.

10. This step checks for an open HO2S signal or low circuit which can cause the HO2S heater to appear not to be operating correctly. It is important to check these circuits before replacing the sensor.