Diagnostic trouble code (DTC) information ECM-221C

Condition 

Fig 1: Identifying Rear Heated Oxygen Sensor

Courtesy of VOLVO CARS OF NORTH AMERICA.

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 a rich fuel/air mixture. 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 rich fuel / air mixture.

Substitute Value 

• None.

Possible Source 

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

Fault symptom[s] 

• Malfunction indicator lamp (MIL) lit.