Diagnostic trouble code (DTC) information

Condition

Fig 1: Identifying Rear Heated Oxygen Sensor (HO2S)

Courtesy of VOLVO CARS OF NORTH AMERICA.

The control module controls preheating by pulsing the current to the PTC-element. Pulse lengths are dependent on heated oxygen sensor (H02S) temperature.

Diagnostic trouble code (DTC) ECM-2B2A is stored if the control module registers that the signal is constantly 2.5 V, higher than 3.5 V at current pulse or lower than 2.3 V at no pulse.

The control module also registers the heated oxygen sensor (H02S) temperature by measuring resistance in the PTC-element. The probe temperature is then compared with a calculated temperature.

Diagnostic trouble code (DTC) ECM-2B2A is stored for a faulty signal if the control module registers that the actual probe temperature is lower than the calculated temperature.

Substitute Value

fuel trim shut off.

Possible Source

Signal too high:

short-circuit to supply voltage in the signal cable
defective heated oxygen sensor (HO2S).

Signal too low:

short-circuit to ground in the signal cable
defective heated oxygen sensor (HO2S).

Signal missing:

contact resistance and oxidation
open-circuit in power supply from system relay.

Faulty signal:

defective heated oxygen sensor (HO2S).

Fault symptom[s]

MIL-lamp lights.