The P0621 fault code is a general code that indicates a fault in the generator lamp “L” control circuit . The generator lamp is an indicator light that indicates alternator operation and charging system. The generator lamp control circuit provides communication between the powertrain control module (PCM) and the alternator.
The causes of the P0621 error code may be:
Alternator faulty or damaged
Alternator control module faulty or damaged
There is a problem with the fuse box or fuses.
Generator lamp control circuit is open, shorted or loose
System voltage is abnormal
PCM faulty or damaged
Symptoms of the P0621 error code may include:
Engine fault light on
Alternator not charging or overcharging
Battery dead or corroded
Electrical accessories not working or working incorrectly
Entering the vehicle into safe mode
How to detect error code P0621? You can follow the steps below:
Read and save fault codes from vehicle memory with OBD-II scanner
Check vehicle history, service records and driver complaints
Clear fault codes and take the vehicle for a test drive
If the fault code reoccurs, check the power and ground connections to the PCM.
Visually inspect all components, wiring and connectors of the generator lamp control circuit and check for any damage, cuts, shorts or looseness.
Use the appropriate tester to test the alternator, alternator control module, and fuses.
Make necessary repairs or replacements
To fix the P0621 error code, you can:
Repair or replace alternator, alternator control module or fuses
Repair or replace wiring, connections or connectors in generator lamp control circuit
Check system voltage and repair or replace charging system components if necessary
Repair or reprogram PCM
Clear fault codes and take the vehicle for a test drive
The P0621 error code is quite important because a fault in the generator lamp control circuit can affect the operation, performance and efficiency of the vehicle's electrical system. Also, a generator lamp control circuit fault can cause the vehicle to not start at another time. Therefore, if you see this fault code, you need to take your vehicle to a specialist as soon as possible.
Things to consider regarding the P0621 error code are:
If the PCM is faulty or damaged, check if your vehicle is under warranty. In some cases, replacing this component may be free.
Before checking all components of the generator lamp control circuit, fully charge the battery and clean and tighten the battery cables. This may prevent some false readings.
To find the problem in the generator lamp control circuit, use a multimeter or test lamp and measure the voltage and resistance in the circuit. Locate and repair any opens, shorts or looseness in the circuit.
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