Advanced Diagnostics

Advanced Diagnostics - DTC P0134: Air/Fuel Ratio (A/F) Sensor (Sensor 1) Heater System Malfunction (Engine Type: K20Z3)






General Description
The air/fuel ratio (A/F) sensor (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 A/F sensor does not activate, and the exhaust emissions deteriorate. The engine control module (ECM) monitors the A/F sensor internal resistance.

1. When the A/F sensor does not activate for a set time after the A/F sensor heater is turned on (with high A/F sensor internal resistance), a malfunction of the A/F sensor heater is detected, and a DTC is stored.
2. When the A/F sensor heater cycles ON and OFF for a set time. The heater's state is detected by monitoring the internal resistance of the A/F sensor. If the resistance remains high when the heater is ON, a malfunction of the A/F sensor heater is detected, and a DTC is stored.
Because the effect on engine control differs according to the A/F sensor internal resistance, there are two types of malfunction detection threshold levels. When either one is reached, a malfunction is detected.

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






Enable Conditions






Malfunction Threshold

Malfunction determination 1 - From start up
The A/F sensor internal resistance value is 90 Ohms or more for at least 40 seconds right after the engine starts.

Malfunction determination 2 - Hot
- The A/F sensor internal resistance value is 70 Ohms or more for at least 15 seconds.
- The A/F sensor internal resistance value is 90 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 50 °F (10 °C) or less, leave the vehicle for 2 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 ECM 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.