Diagnostic trouble code (DTC) information

Condition 

Fig 1: Identifying Rear Heated Oxygen Sensor (HO2S)

Courtesy of VOLVO CARS OF NORTH AMERICA.

The control module checks the rear heated oxygen sensor (HO2S) dynamics. The control module checks that the probe has registered both lean and rich fuel mixtures. If this is not the case, the control module alters the fuel mixture. Diagnostic trouble code (DTC) ECM-2A1A is stored if the rear probe still does not register lean or rich fuel mixture.

At fuel shut-off, the probe must show lean fuel mixture. Diagnostic trouble code (DTC) ECM-2B1A is stored if the switch over time from lean to rich fuel mixture is too long.

Substitute Value 

• twin heated oxygen sensor (HO2S) control disabled
• Three-way catalytic converter (TWC) diagnostic is disabled

Possible Source 

• leakage in the exhaust system
• defective heated oxygen sensor (HO2S).

Fault symptom[s] 

• malfunction indicator lamp (MIL) lit.