Oxygen Sensor Heater Monitor (Both Upstream & Downstream O2)

Perform the following:

• Engine running at least 5 minutes.
• Shut the Engine off.
• Minimum battery voltage with engine off is more than 10 volts.
• The PCM delays for 5 seconds.
• The PCM keeps the power to the O2S Heaters off (keeps the ASD Relay off for now).
• The PCM begins pulsing the O2 Sensors with 5 volts for 35 milliseconds every 1.6 Seconds.
• The PCM then monitors the O2S voltage before and during each pulse.

If the initial voltage difference between the Pulse on and Pulse off minus the next Pulse on and Pulse off difference is more than 1.5 volts, the Oxygen Sensors are too cool and all testing is stopped. If the initial voltage difference minus the next voltage difference is less than 1.5 volts, the Oxygen Sensors are properly heated and the testing continues. Next, the cool-down phase begins. The PCM continues to pulse the Oxygen Sensor with 5 volts and then back to .45 volts. The PCM monitors and stores the first Pulse on and the first Pulse off voltages and then subtracts them from each other. The PCM then subtracts the voltage difference from each new set of Pulse on and Pulse off reads, to the difference of the voltage reads taken just before.

Once the PCM sees a difference between readings of at least .490 volts, the sensors have properly cooled and the O2 Sensor Heaters are ready to be tested. If 3:40 minutes have elapsed and still a voltage difference of .490 has not been reached, the PCM begins heating the O2 Sensor that has cooled and disables testing on the O2 Sensor which has not fully cooled. If all Oxygen Sensors have cooled properly, the PCM then grounds the ASD Relay (to provide the O2 Heaters with voltage). The PCM continues to Pulse 5 volts to all O2 Sensors after the ASD Relay is turned on.

The O2 Heaters can pass by one of two methods: First, with the 5-volt Pulse on, the PCM compares to the next 5-Volt Pulse on value. If the voltages between spikes (on Pulses) has decreased by .157 volts. The O2 Heater monitor passes and all testing is stopped this trip. Secondly, the voltage difference between the Pulse on voltage is compared to next Pulse on voltage and is less than the prior voltage Pulse on, for 10 out of the 30 Pulses (33%), this indicates a Heating Trend and the O2 Heater Passes. If neither a Heating Trend nor the Absolute voltage is reached, the O2 Heater monitor fails 1 trip and the Freeze Frame Data is stored.