Diagnostic Trouble Code (DTC) Information ECM-U012087

Condition 

Fig 1: Identifying Alternator Control Module (ACM)

Courtesy of VOLVO CARS CORPORATION

The engine control module (ECM) regulates the alternator charge voltage (via LIN communication) on request of the central electronic module (CEM) (via CAN communication). The diagnostic trouble code is generated if the engine control module (ECM) detects that there is no communication with the alternator control module (ACM).

The diagnostic trouble code can be diagnosed when the ignition is on.

Substitute Value 

• The alternator control module (ACM) (charge regulator) charges with a fixed voltage of 13.8 V.

Possible Source 

• Contact resistance or oxidation on connections
• Short-circuit between the LIN wiring
• Open-circuit in the LIN wiring
• Internal fault in another control module in the same part of the LIN network.
• Damaged alternator control module (ACM) (charge regulator).
• The alternator with charge regulator is not designed for LIN communication.

Fault symptom[s] 

• Battery discharged.
• Low starter motor RPM.
• The engine judders under acceleration