Circuit Description

PCM provides about .45 volt reference to Heated Oxygen Sensor (HO2S). HO2S sensor signal varies from about one volt when exhaust is rich to about .1 volt when exhaust is lean. When ignition is turned on, battery voltage is supplied to HO2S heater to provide for faster sensor warm-up, allowing sensor to become active in a shorter period of time. PCM reads amount of time necessary for sensor to become active after start-up. If too much time was required for HO2S to become active, DTC P0135 will set.

Conditions required to set DTC are:

• No related DTCs set.
• ECT and IAT less than 90°F (32°C) at start-up.
• Difference between ECT and IAT no greater than 9°F (5°C).
• Ignition voltage is 11-16.6 volts.
• MAF less than 18 grams per second during sample period.
• TP sensor angle is less than 40 percent.
• Front HO2S voltage does not change more than 148 mV from bias voltage (.4-.5 volts) for an extended period.