P0623 OBD-II Trouble Code: Generator Lamp Control Circuit

Check Engine Light

P0623 trouble code definition

A P0623 trouble code is related to a vehicle’s engine control unit (ECU) and its connection with the battery’s voltage.

What the P0623 code means

P0623 is an OBD-II generic code for a voltage problem between the ECU and the generator control module that helps a vehicle start properly.

What causes the P0623 code?

There could be a variety of causes for a P0623, but the most common culprits are:

  • Bad battery connection
  • Bad alternator connection
  • Weak or dead battery
  • Bad alternator
  • Bad ECU

What are the symptoms of the P0623 code?

Symptoms can vary for a P0623, and some codes will have no impact on the vehicle. Other symptoms include:

  • Weak starting
  • No starting
  • Weak charging
  • No charging

How does a mechanic diagnose the P0623 code?

Because a P0623 is mostly related to a vehicle’s battery and alternator, your mechanic will first test both to ensure voltage and output are within the manufacturer’s parameters. If they are not, either faulty part will be replaced. If they check out however, your mechanic will then ensure wiring and connectors are in good condition, replacing as necessary.

A good cleaning of battery terminals, wire connections and grounds can also help ensure an intermittent code does not return after it’s cleared.

Common mistakes when diagnosing the P0623 code

Like any generic ECU control circuit code, the cause can difficult to find, so it’s important to start with the easiest first before replacement parts like an alternator, battery or ECU are bought. While this may not save time, it will save money.

How serious is the P0623 code?

A P0623 may cause a vehicle not to start or worse, charge while you’re out driving. How the vehicle drives with this code will determine how severe the problem is.

What repairs can fix the P0623 code?

The most common repairs for a P0623 are as follows:

Additional comments for consideration regarding the P0623 code

P0623s are not very common codes, but if you get one, chances are you’re driving a diesel. Because this code is mostly undocumented, chances are high it will coincidental to a different, more obvious issue, i.e. low battery voltage.

Need help with a P0623 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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