Diagnostic trouble code (DTC) information ECM-421B

Condition 

Fig 1: Identifying Evaporative Emission System (EVAP) Valve

Courtesy of VOLVO CARS OF NORTH AMERICA.

The diagnostic trouble code (DTC) is stored if the engine control module (ECM) detects that there is no signal from the evaporative emission system (EVAP) valve.

The diagnostic trouble code (DTC) can be diagnosed when the ignition is switched on.

Substitute Value 

• twin heated oxygen sensor (HO2S) control disabled.

Possible Source 

• Open-circuit in the signal cable
• Damaged evaporative emission system (EVAP) valve
• Contact resistance in the terminals
• Open-circuit in the power cable.

Fault symptom[s] 

• Malfunction indicator lamp (MIL) lit.