P0622 is a somewhat rare OBD2 fault code. It is a general code, meaning it has the same definition for all vehicles. Indicates that the generator field coil control circuit is malfunctioning and may be difficult to diagnose.
P0622 Meaning: Generator field coil control circuit failure
“Generator field coil” is not a term that is used much, even if you are familiar with working on cars and trucks. Here’s a quick explanation of what exactly P0622 means:
Generator field control circuit F
The generator field coil is a fixed part of the alternator. If you’ve ever held a new alternator, you’ll be able to see the copper windings inside. It’s not as easy to see once it’s dirty. In the photo above you can easily see the generator field coil.
The generator field control circuit controls the generator field coil. The PCM will send the ignition signal from the generator to the alternator. Afterward, the voltage regulator will begin to control the alternator output on its own.
You cannot replace the generator field coil by itself. The entire alternator would have to be replaced.
When the PCM commands the alternator to start, it can detect a problem in the generator field control circuit. If it does, it will throw P0622.
Symptoms of P0622 include:
- Dead battery
- Ignition failures (due to low voltage)
- Slow start/Won’t start
- Battery or alternator light comes on
- Check engine light with P0622 (potentially with other codes)
Most P0622 symptoms are related to low voltage coming from the alternator.
P0622 Causes + Diagnosis
Here are the probable causes of P0622, as well as a good order to view them.
P0622 is difficult to diagnose at home, as it requires special diagnostic equipment that most people do not have for some parts.
1. Check other codes
Other codes related to the charging system can help you narrow down the reason why P0622 appeared in your PCM memory.
Make sure to record the codes that appeared and then clear the memory. You should also record the freeze frame data if you know how to read it. It will be valuable if the code ends up appearing intermittently.
Now that you’ve captured this data, it’s time to clear the codes and see if you can get the code to appear again.
2. Check the battery/chassis/motor ground cable
Although not the most likely cause of P0622, bad chassis ground wires are known to cause problems with the generator field control circuit.
If you find a loose or corroded ground wire, clean it, make sure it is securely screwed down, and clear the code. Maybe you’ll get lucky and that will be solved.
3. Check the generator field control circuit
This is going to involve getting the wiring diagram for your exact model year and engine combination. Once you have them, you can start testing the wiring harness.
- Make sure the battery is sufficiently charged.
- Confirms that there is battery voltage in the generator field control circuit. (If there is, the alternator will probably need to be replaced.) If there is no tension, you will have to find out why.
- If the alternator outputs a proper voltage, check the field control circuit fuses and relays to ensure they are receiving power.
- Inspect the wiring harness for signs of damage. Being in the engine compartment can be difficult for the wiring harness.
- If all the wiring seems fine, it’s time to consider a new controller. You will most likely have to program it for your vehicle if you buy it secondhand.
4. Bad alternator
A bad alternator can cause the P0622 code, but it is not very likely. People often replace the alternator and battery when the code appears and still have the battery light on, and the P0622 code appears again.
While the generator field coil is inside the alternator, the controller is not. Therefore, there is no guarantee that replacing the alternator will solve the problem causing the code.
P0622 can be a difficult code to diagnose at home. Although there are some things you can do, you may have to leave it to a professional.