Diagnostic trouble code (DTC) information

Condition 

Fig 1: Identifying Heated Oxygen Sensor (HO2S)

Courtesy of VOLVO CARS OF NORTH AMERICA.

The control module monitors how long it takes for the front heated oxygen sensor (HO2S) to switch between high and low (from rich to lean fuel mixture). Diagnostic trouble code (DTC) ECM-28 is stored if the period is too long or if the difference between the adaptation for the front and rear heated oxygen sensors (HO2S) is greater than a certain value.

Substitute Value 

• None.

Possible Source 

• Contact resistance in the terminals
• Leakage in the exhaust system between the front and the rear heated oxygen sensor (HO2S)
• Leakage in the exhaust system between the exhaust manifold / turbocharger (TC) and the front heated oxygen sensor (HO2S)
• Air leakage in the intake system
• Defective front heated oxygen sensor (HO2S)
• Defective rear heated oxygen sensor (HO2S).

Fault symptom[s] 

• Malfunction indicator lamp (MIL) lit.