Error Code P0622 is defined as Generator Lamp “L” Control Circuit Malfunction. This is a generic trouble code, meaning it applies to all vehicles equipped with the OBD-II system, especially those made since 1996 up to present. It typically applies (but not limited to) to cars from Chevrolet, Dodge, Ford, Jeep, Land Rover, and Toyota. Specifications on the definition, troubleshooting, and repairs, of course, vary from make, model, and powertrain configuration.

When Error Code P0622 is detected, this means the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) has determined a malfunction with the generator field coil control circuit. The F simply means the lamp control circuit.

The field coil may be the most recognizable from its windings. They’re visible through vent holes on most alternators. Field coil surrounds the generator armature and is kept stationary in the housing of the alternator.

The PCM oversees the continuity and voltage level of the generator field control circuit each time the engine is running. The generator field coil plays a very important part of the general operation and maintaining of battery charge levels.

Every time the ignition is on and the PCM is energized, both the APP sensor and TPS self-tests will commence. Aside from running the internal controller self-test, the CAN (controller area network) also compares signals from each individual module to ensure that each controller is running correctly.

If there’s a problem detected while monitoring the field control circuit, then Error Code P0622 will be stored, and Check Engine light will be activated. Depending on the severity of the condition, it may take multiple failure cycles before the Check Engine light lights up.

Common Symptoms

This code shows a number of drivability issues, such as:

  • Engine drivability issues
  • Engine stalling when idling
  • Inadvertent engine shutoff
  • Delayed engine cranking (especially if it’s cold)

Other codes may be stored.

Possible Causes

  • Defective PCM
  • PCM programming error
  • Open or shorted generator field control circuit
  • Faulty alternator/generator

How to Check

As with most error codes, diagnosing this fault requires a diagnostic scanner, battery/alternator tester, DVOM (digital volt/ohmmeter), and a reliable vehicle information source.

Look for the vehicle information from the TSB (technical service bulletin) that is parallel with the code stored, vehicle (year, make, and model), engine, and symptoms. If you find the right TSB, then this will give you the correct diagnostic information.

Start the diagnosis by connecting the scanner to the vehicle’s diagnostic port and retrieve all stored codes, as well as their freeze frame data. You may write this information down, in case the problem proves to be intermittent. After recording necessary data, clear the codes and then take the vehicle for a test drive until the code resets, or the PCM enters readiness mode. If the PCM enters Readiness Mode, that means the code is intermittent, and the problem must develop further before you can accurately diagnose and do the necessary repair.

Then, test the battery using battery/alternator and make sure it’s charged sufficiently. If it’s not, then test the alternator/generator. Make sure you follow the specifications and instructions set by the manufacturer and the maximum voltage output requirements for the alternator and battery. If the alternator/generator is not charging, then go to the next step.

Use vehicle information source to obtain component locations, connector face views, connector pin-out charts, wiring diagram, and diagnostic flow chart related to your vehicle’s error code.

Then, use the DVOM to the test controller power supply fuses and relays. Next, test and replace any blown fuses as necessary. Fuses must be tested with circuit loaded.

If all fuses and relays are running well, check whether the controller related wiring and harness are in order. You may also want to check chassis and engine ground junctions. Again, use your vehicle information source to obtain ground locations as related circuits. Test ground integrity using the DVOM.

Then, check the system controllers for any signs of water, heat, or collision damage. Any controller that is damaged, especially by water, is considered defective and must be replaced.

If controller power and ground circuits are intact, then there’s a good chance the controller is defective, or there’s a programming error in the controller. Thus, controller replacement requires reprogramming. In some cases, you may want to get aftermarket reprogrammed controllers. Some vehicles and controllers require on-board reprogramming that may be done only through the dealership or a qualified shop.

How to Fix

Depending on your diagnosis, common repairs for this code include:

  • Replacement of faulty electronics
  • Disconnecting all CAN pins and testing them individually
  • Replacement of control module ground strap

There are multiple routes technicians may take when repairing this problem, and this usually depends on which module reported the problem and its status.

This code could potentially cause severe problems for the vehicle, as it could cripple the vehicle’s capabilities. With that being said, the problem with CAN could mean something more widespread on the vehicle’s electrical functions.

The coil field is an integral component of the alternator, and cannot be replaced separately.

Connect the negative test lead of the DVOM to ground, and the positive test lead to battery voltage to test for the controller’s ground integrity.