Advanced Diagnostics

Advanced Diagnostics - DTC P0134: Rear Air/Fuel Ratio (A/F) Sensor (Bank 1, Sensor 1) Heater System Malfunction






General Description
The rear air/fuel ratio (A/F) sensor (bank 1, sensor 1) is activated by warming the element with a heater and by maintaining a steady high temperature to accurately calculate the air/fuel ratio. If the heater does not properly heat the element, the rear A/F sensor does not activate, and the exhaust emissions deteriorate. The powertrain control module (PCM) monitors the rear A/F sensor internal resistance.

1. When the rear A/F sensor does not activate for a set time after the rear A/F sensor heater is turned on (with high rear A/F sensor internal resistance), a malfunction of the rear A/F sensor heater is detected, and a DTC is stored.
2. When the rear A/F sensor heater cycles ON and OFF for a set time, and the resistance remains high when the heater is ON, a malfunction of the rear A/F sensor heater is detected, and a DTC is stored.

Monitor Execution, Sequence, Duration, DTC Type, OBD Status






Enable Conditions






Malfunction Threshold

Malfunction determination 1 - From start up
The rear A/F sensor (bank 1, sensor 1) internal resistance value is 200 Ohms or more for at least 40 seconds right after the engine starts.

Malfunction determination 2 - Hot
The rear A/F sensor (bank 1, sensor 1) internal resistance value is 270 Ohms or more for at least 1.0 second.

Driving Pattern
Start the engine, and let it idle for at least 1 minute. When engine coolant temperature is 14 °F (-10 °C) or less, leave the vehicle for 4 minutes or more.

Diagnosis Details

Conditions for setting the DTC
When a malfunction is detected during the first drive cycle, a Pending DTC is stored in the PCM memory. If the malfunction returns in the next (second) drive cycle, the MIL comes on and a Confirmed DTC and the freeze data are stored.

Conditions for clearing the DTC
The MIL is cleared if the malfunction does not return in three consecutive trips in which the diagnostic runs. The MIL, the Pending DTC, the Confirmed DTC, and the freeze data can be cleared with the scan tool Clear command or by disconnecting the battery.