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 the heater and by maintaining it at a steady high temperature to accurately calculate the air/fuel (A/F) ratio. The rear A/F sensor does not become active when the element is not properly heated due to a heater malfunction, 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 within a set time after the rear A/F sensor heater starts to warm up (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 within a set time, and the resistance remains high when the heater is ON, a malfunction in 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
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
The rear A/F sensor (bank 1, sensor 1) internal resistance value is 270 ohms or more for at least 1 second.

Driving Pattern
Start the engine, then 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.