P0135

Heated Oxygen Sensor (HO2S) Heater Circuit Sensor 1:

Heated Oxygen Sensor (HO2S) Heater Circuit Sensor 1 (continued):

Heated Oxygen Sensor (HO2S) Circuit Sensor 1:

Circuit Description

Heated oxygen sensors 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 (HO2S sensor 1) to become active. The oxygen sensor heater is required by catalyst monitor (HO2S sensor 2) to maintain a sufficiently high temperature. This allows accurate exhaust oxygen content readings from the engine.


Conditions for Setting the DTC

^ Resistor voltage less than 2.5 volts with the heater off.

^ Resistor voltage greater than 0.31 volts with the heater on.

^ One of the above conditions present for 5 seconds.


Action Taken When the DTC Sets

^ The Malfunction indicator Lamp (MIL) will illuminate after two consecutive ignition cycles in which the diagnostic runs with the fault active.

^ The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame buffer.

Conditions for Clearing the MIL/DTC

^ The MIL will turn "OFF" after three consecutively passing cycles without a fault present.

^ A History DTC will clear after 40 consecutive warm-up cycles without a fault.

^ DTC(s) can be cleared by using a scan tool or by disconnecting the PCM battery feed.

Diagnostic Aids

Check the following conditions:

^ Poor connection at PCM. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.

^ Damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the HO2S 1 display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the HO2S 1 display will indicate the location of the fault.

If DTC P0135 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set.

If any wiring repairs need to be made, Refer to Repair Procedures in Diagrams.

Test Description

Number(s) below refer to the step number(s) on the Diagnostic Table.


1. The Powertrain OBD system check prompts the technician to complete some basic checks and store the freeze frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

2. Determines if the fault is present.

3. The HO2S 1 is powered by the IG fuse located in the Junction Block.

5. Measures the resistance of the heater portion of the HO2S 1.