Check the 'Possible Causes' listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector pins.
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What is the Cost to Diagnose the Code?
Labor: 1.0
The cost to diagnose the P0621 GMC code is 1.0 hour of labor. The diagnosis time and labor rates at auto repair shops vary depending on the location, make and model of the vehicle, and even the engine type. Most auto repair shops charge between $75 and $150 per hour.
What are Code Possible Symptoms?
Engine Light ON (or Service Engine Soon Warning Light)
What Does the P0621 GMC Code Mean?
The Engine Control Module (ECM) uses the Generator turn ON control circuit to control the load of the generator on the engine. A high-side driver in the ECM applies a duty-cycled voltage to the voltage regulator. The duty cycle controls the voltage regulator to turn the field circuit ON and OFF. The ECM monitors the state of the generator turn ON control circuit. The ECM should detect low voltage on the generator and turn on the control circuit when the ignition is ON and the engine is OFF, or when the charging system malfunctions. With the engine running, the ECM should detect a high voltage when the duty cycle voltage is commanded high and a low voltage when the duty cycle voltage is commanded low on the generator turn on the control circuit. The will be set when the ECM detects greater than 3.5 V on the generator control circuit for 5 s with the ignition ON and engine OFF, or the ECM detects a low or high voltage for 15 s on the generator control circuit with the engine running.
P0621 GMC Code - Generator Lamp L Control Circuit Malfunction