OBD-II Trouble Code Description for P0621 GMC

Generator Lamp/L Terminal Circuit

What does this mean?

OBD2 Code P0621 GM definition:
The Engine Control Module (ECM) or Powertrain Control Module (PCM) uses the generator turn on signal circuit to control the load of the generator on the engine. A high side driver in the ECM/PCM applies a voltage to the voltage regulator. This signals the voltage regulator to turn the field circuit ON and OFF. The ECM/PCM monitors the state of the generator turn on signal circuit. The ECM/PCM should detect low voltage on generator turn on signal circuit when the ignition is ON and the engine is OFF, or when the charging system malfunctions. With the engine running, the ECM/PCM should detect high voltage on the generator turn on signal circuit. The ECM/PCM performs Ignition ON and RUN tests to determine the status of the generator turn on signal circuit.

Symptoms

Possible sumptoms of OBD code P0621 GM
– Engine Light ON (or Service Engine Soon Warning Light)

Causes

Possible causes of OBD code P0621 GM
– Generator circuit – Generator circuit short to fround – Generator circuit open/high Resistance – Generator circuit short to voltage – Bad generator/alternator – Faulty ECM/PCM The Error code is generally activated on detection of the following conditions: – During the Ignition ON test, the ECM/PCM detects high voltage on the generator turn on signal circuit for 5 seconds. – During the RUN test, the ECM/PCM detects low voltage on the generator turn on signal circuit for 15 seconds.

Possible Solutions

– Replaced alternator/generator