P0135
DTC P0135 HO2S Heater Circuit Bank1 Sensor1
Circuit Description
IMPORTANT: If the voltage is measured with a 10 Megohm DMM, the voltage may read as low as 0.32 volt.
The HO2S does not produce a voltage at temperatures below 200 °C (392 °F). When the HO2S is below 200 °C (392 °F), the VCM will default to a 450 mV reference voltage. When the HO2S temperature is below 200 °C (392 °F), the oxygen sensor voltage displayed on the scan tool will be near the 450 mV reference signal. The VCM holds the fuel control system in open loop operation until the sensor reaches operating temperature. The HO2S heater provides for a faster sensor warm-up which allows the sensor to become active in a shorter period of time. When the HO2S temperature exceeds 200 °C (392 °F), the sensor begins producing a voltage that varies in response to exhaust oxygen levels. This voltage ranges from a high of approximately 900 mV under rich exhaust conditions, to a low of approximately 100 mV under lean exhaust conditions. These voltage transitions from rich-to-lean and lean-to-rich occur rapidly when the VCM is in control of the air/fuel ratio (closed loop operation).
This DTC determines if the HO2S heater circuit is functioning properly by monitoring the amount of time required for the HO2S to reach operating temperature. This DTC sets when the VCM fails to detect HO2S voltage transitions above and below the bias range within a specified amount of time. Possible cause of this DTC are listed below.
- An open circuit in either the HO2S ignition feed or the HO2S heater ground circuits
- An HO2S heater element problem
Conditions for Running the DTC
IMPORTANT: This test is void if the system voltage remains outside the specified range for more than 4 seconds.
- The system voltage is between 11.7 - 17 volts
- The MAF is less than 27 g/s
- The engine run time is greater than 2 seconds
- The ECT sensor is less than 33 °C (91 °F)
- The IAT is less than 33 °C (91 °F)
- The deference between the ECT and IAT is no more than 5 °C (41 °F)
Conditions for Setting the DTC
The O2 sensor voltage remains within 150 mV of its startup voltage for 130 seconds after cold start.
Action Taken When the DTC Sets
The VCM illuminates the MIL after 2 consecutive test failures.
Conditions for Clearing the MIL/DTC
- The VCM turns OFF the MIL after 3 consecutive drive trips when the test has Run and Passed.
- 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 is more than 70 °C (158 °F) during the same ignition cycle).
- Use the scan tool Clear Information function.
Diagnostic Aids
IMPORTANT: Never solder the HO2S wires. For proper wire and connection repairs, refer to Wiring Repairs or Connector Repairs.
An intermittent may be caused by any of the following conditions:
- A poor connection
- Rubbed through wire insulation
- A broken wire inside the insulation
Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Refer to Intermittents and Poor Connections Diagnosis.
If a repair is necessary, then refer to Wiring Repairs or Connector Repairs.
Step 1:
Steps 2 - 3:
Steps 4 - 6:
Steps 7 - 11:
Steps 12 - 13:
Steps 14 - 15:
Test Description
The number(s) below refer(s) to the step number(s) on the Diagnostic Table
2. As the heater warms the oxygen sensor to operating temperature, the HO2S will output a voltage in relation to the amount of oxygen in the exhaust. With the ignition ON and the engine OFF the exhaust usually contains a high oxygen content. With the engine OFF the HO2S voltage will usually decrease from the initial (bias) voltage due to the high oxygen content.
4. This step checks for proper HO2S heater ignition feed and ground supply.
5. This step checks for proper VCM and signal circuit operation.