Oxygen Sensor Heater Monitor

The Oxygen Sensor Heater Monitor begins after ignition has been turned OFF. The PCM sends a 5 volt bias to oxygen sensor every 1.6 seconds. The PCM keeps it biased for 35 ms each time. As sensor cools down, resistance increases and PCM reads increase in voltage. Once voltage has increased to a predetermined amount, higher than when test started, oxygen sensor is cool enough to test heater operation.

When oxygen sensor is cool enough, PCM energizes ASD relay. Voltage to O2 sensor begins to increase temperature. As sensor temperature increases, internal resistance decreases. The PCM continues biasing 5 volt signal to sensor. Each time signal is biased, PCM reads a voltage decrease. When PCM detects a voltage decrease of a predetermined value for several biased pulses, test passes.

The heater elements are tested each time engine is turned OFF if all enabling conditions are met. If monitor fails, PCM stores a maturing fault and a Freeze Frame is entered. If 2 consecutive tests fail, a DTC is stored. Because ignition is OFF, MIL is illuminated at beginning of next key cycle.

Enabling Conditions -  The following conditions must be met for PCM to run oxygen sensor heater test:

• Engine run time of at least 5.1 minutes.
• Engine run time at a predetermined speed and throttle opening.
• Key OFF power down.
• Battery voltage of at least 10 volts.
• Sufficient Oxygen Sensor cool down.

Pending Conditions -  There are not conditions or situations that prompt conflict or suspension of testing. The oxygen sensor heater test is not run pending resolution of MIL illumination due to oxygen sensor failure.

Suspend -  There are no conditions which exist for suspending Heater Monitor.