P0135

DTC P0135 Heated Oxygen Sensor (HO2S) Heater Circuit Malfunction (Bank 1, Sensor 1):

Heated Oxygen Sensor (HO2S 1) Circuit:

CIRCUIT DESCRIPTION
The Vehicle Control Module-A (VCM-A) supplies a voltage of approximately 0.45 volt (450 mV) between VCM-A pins "BL21" and "BL7".

NOTE: If this voltage is measured using a 10 megohm digital voltmeter, the voltage may read as low as 0.32 volt. The Heated Oxygen Sensor (HO2S) varies the voltage within a range of about 1 volt (1000 mV) if the exhaust is rich to as low as 0.10 volt (100 mV) if the exhaust is lean.

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

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

DTC PO135 WILL SET WHEN
^ Throttle position is less than 37% for 3 seconds.
^ Engine run time is greater than 2 seconds.
^ Engine coolant temperature less than 32°C (89°F).
^ Max time: 120 seconds.
^ Intake Air Temperature (IAT) less than 32°C (89°F).
^ The time to obtain ±0.150V from the mean H02S bias voltage (0.45V) is to long based on a calculated time Value.

ACTION TAKEN (VCM-A WILL DEFAULT TO)
With a current DTC P0135 set, the VCM-A will turn "ON" Malfunction Indicator Lamp (MIL) after 2 consecutive test failures.

DTC P0135 WILL CLEAR WHEN
The VCM-A will turn the MIL "OFF" after three consecutive trips without a fault condition present. A history DTC will be cleared if no fault conditions have been detected for forty warm-up cycles [coolant temperature has risen 22°C (40°F) from start-up coolant temperature and engine coolant temperature exceeds 71°C (160°F) that same ignition cycle] or the Tech 1 clearing feature has been used.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. This step determines if DTC PO135 is the result of a hard failure or an intermittent condition. With the ignition "ON," engine "OFF," the HO2S 1 voltage displayed on the Tech 1 should gradually change 0.150 volt, indicating that the heater is working properly. HO2S voltage can rise as high as 975 mV before it toggles back down. The main thing to look for is a change.
2. Probing terminal "D" of the HO2S 1 connector verifies if voltage is available to the HO2S 1 heater.
3. If voltage is available at the connector, then it becomes a good voltage source to check for a ground at terminal "C".
4. Determines if voltage is not available at the HO2S 1 due to an open fuse or open ignition feed circuit. If the fuse is open, determine if it was due to a short in the ignition feed circuit before replacing the fuse.

DIAGNOSTIC AIDS
An intermittent may be caused by rubbed through wire insulation or a wire contacting the exhaust.

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