P0135

Diagnostic Chart:

Wiring Diagram:

Circuit Description
The VCM supplies a voltage of approximately 0.45 volt (450 mV) between the HO2S High and HO2S Low circuits. If a 10 megohm digital voltmeter measures this voltage, the voltage may read as low as 0.32 volt. The Heated Oxygen Sensor (HO2S) varies the voltage within a range of about 1.0 volt (1000 mV) if the exhaust is rich to as low as 0.1 volt (100 mV) if the exhaust is lean.

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 an active in a shorter period of time. The sensor will remain active during a long extended idle. The Diagnostic Trouble Code (DTC) P0135 determines if the HO2S is functioning properly by checking the response time of the sensor. This DTC is a type B DTC.

Conditions for Setting the 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 45 grams per second.
^ 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 8°C.
^ The elapsed time to obtain the +/-0.150 volts from the HO2S bias voltage (0.300-0.600 volts) is greater than the calculated value.

Action Taken When the DTC Sets
With a current DTC set, the VCM turns on the Malfunction Indicator Lamp (MIL) after 2 consecutive test failures.

Conditions for Clearing the MIL/DTC
The VCM turns the MIL off after 3 consecutive driving trips without a fault condition present. A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (coolant temperature has risen 40°F from the start-up coolant temperature and the engine coolant temperature exceeds 160°F during that same ignition cycle) or the scan tool clearing feature has been used.

Diagnostic Aids

^ 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.
- Poor terminal to wire connection.
- Damaged harness.

NOTE: Never solder the HO2S wires. For proper wire and connection repairs refer to Wiring Repairs in Engine Electrical.

Test Description
The numbers below refer to the step numbers on the diagnostic table.

2. This step determines if the DTC P0135 is the result of a hard failure or an intermittent condition present. With the ignition ON and the engine off, the HO2S Bank 1, Sensor 1 voltage displayed on the scan tool should gradually change to 0.150 volt, indicating that the heater is working properly. The HO2S voltage can rise as high as 975 mV before it toggles back down. The main thing to look for is a change.
3. Probing the terminal D of the HO2S Bank 1, Sensor 1 connector verifies if the voltage is available to the HO2S Bank 1, Sensor 1 heater.