Diagnostic Trouble Code (DTC) Information ECM-221B

Condition

Fig 1: Identifying Rear Heated Oxygen Sensor

Courtesy of VOLVO CARS CORPORATION

The engine control module (ECM) monitors the operation of the rear heated oxygen sensor (HO2S) by checking its signal. The engine control module (ECM) checks that the probe has registered both rich and lean fuel/air mixtures. If this is not the case, the engine control module (ECM) changes the fuel/air mixture. The diagnostic trouble code (DTC) is stored if the rear probe has still not registered a lean or rich fuel / air mixture.

NOTE:

At fuel shut-off, the probe must show a lean fuel/air mixture. The diagnostic trouble code (DTC) is stored if the switch-over time to a lean fuel/air mixture is too long.

Substitute Value

None.

Possible Source

Leakage in the exhaust system
Damaged rear heated oxygen sensor (HO2S).

Fault symptom[s]

Malfunction indicator lamp (MIL) lit.