Advanced Diagnostics

Advanced Diagnostics - DTC P1172: Rear Air/Fuel Ratio (A/F) Sensor (Bank 1, Sensor 1) Circuit Out of Range High






General Description
If a malfunction causes the rear air/fuel ratio (A/F) sensor (bank 1, sensor 1) signal to the powertrain control module (PCM) to deviate from the normal control area, the rear A/F sensor may still become active after the engine starts, but the air/fuel feedback does not start normally and the emissions deteriorate. When the rear A/F sensor output is out of the normal area, and this condition continues after the rear A/F sensor is active, the PCM detects a malfunction and stores a DTC.

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






Enable Conditions






Malfunction Threshold
A malfunction is detected when the rear A/F sensor (bank 1, sensor 1) output voltage is 4.70 V or more.

Driving Pattern
1. Start the engine. Hold the engine speed at 3,000 rpm without load (in P or N) until the radiator fan comes on, then let it idle.
2. Air/fuel ratio feedback is started while idling, hold for at least 7 seconds.

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.