P0622 is a somewhat rare OBD2 trouble code. It’s a general code, meaning it has the same definition for all vehicles. It indicates the generator field coil control circuit is malfunctioning and can be a bear to diagnose.
P0622 Meaning: Generator Field F Control Circuit Malfunction
“Generator field coil” is not a term that is thrown around a whole lot, even if you are familiar with working on cars and trucks. Here’s a quick explanation of exactly what P0622 means:
Generator Field F Control Circuit
The generator field coil is a stationary part of the alternator. If you’ve ever held a new alternator, you can see the copper windings inside of it. It isn’t so easy to see once it’s dirty. You can see a generator field coil is easily seen in the pic directly above.
The generator field control circuit controls the generator field coil. The PCM will send the generator turn-on signal to the alternator. After that, the voltage regulator will begin controlling the output of the alternator by itself.
You can not replace the generator field coil by itself. The whole alternator would need replacing.
Malfunctioning
When the PCM commands the alternator to turn on, it can detect an issue with the generator field control circuit. If it does, it’ll throw P0622.
Symptoms
Symptoms of P0622 include:
- Dead battery
- Misfiring (due to low voltage)
- Slow crank/No start
- Stalling
- Battery or alternator light illuminated
- Check engine light with P0622 (potentially with other codes)
Most of the symptoms of P0622 are related to the low voltage coming from the alternator.
P0622 Causes + Diagnosis
Here are the likely causes of P0622, as well as a good order to take a look at them in.
P0622 is difficult to diagnose at home, as specialty diagnostic equipment that most folks don’t have is required for some parts.
1. Check for other Codes
Other codes related to the charging system can help you narrow down why P0622 appeared in your PCM’s memory.
Make sure you record any codes that were listed and then clear the memory. You should also record the freeze frame data if you know how to read it. It’ll prove 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 come back.
2. Check the Battery/Chassis/Engine Ground Wire
While it’s not the most likely cause of P0622, bad ground wires to the chassis are known to cause issues with the generator field control circuit.
If you find a loose or corroded ground wire clean it, make sure it’s bolted tightly, and clear the code. Maybe you’ll get lucky, and that’ll take care of it.
3. Check the Generator Field Control Circuit
This is going to involve getting the wiring schematic for your exact model year and engine combination. Once you have them, you can begin testing the wiring harness.
- Make sure that the battery is sufficiently charged.
- Confirm that there is battery voltage on the generator field control circuit. (If there is, then it’s likely that the alternator will need to be replaced). If there’s no voltage, you’re going to need to find out why.
- If the alternator is putting out the proper voltage, check the fuses and relays in the field control circuit to ensure they are getting power.
- Inspect the wiring harness for signs of damage. Being in the engine compartment can be difficult for a wiring harness.
- If all of the wiring looks good, it’s time to consider a new controller. You’ll most likely need to have it programmed for your vehicle if you’re buying it used.
4. Bad Alternator
A bad alternator can cause P0622, but it’s not very likely. People often replace the alternator and the battery when the code comes up and will still end up with the battery light on, and the P0622 code will return.
While the generator field coil is inside the alternator, the controller is not. So it’s no guarantee that replacing the alternator will solve the issue causing the code.
Conclusion
P0622 can be a tough code to diagnose at home. While there are some things you can do, you may have to have it looked at by a professional.