P0622 Code: Generator Field / F Terminal Circuit

The powertrain control module (PCM) controls the alternator/generator and runs diagnostics to make sure it runs properly. When the computer detects the wrong signal from the alternator’s generator field coil control circuit, it will log a code P0622.

What Does the P0622 Code Mean?

The Diagnostic Trouble Code (DTC) P0622 indicates “Generator Field/F Terminal Circuit.”

Most alternators have a field coil around the generator armature. This coil plays a major role in running the generator and charging the battery. Thus, the PCM constantly checks on the generator field control circuit whenever the engine is running.

Whenever you turn on your vehicle’s ignition, the PCM powers up and diagnoses itself several times. Its controller area network (CAN) also checks the signals from the PCM’s individual modules. If the modules aren’t interfacing properly, they may not share important information from the parts they control.

Once the PCM detects a continuity or voltage issue in the generator field control circuit, it will log a code P0622. If the problem repeats itself or proves very serious, the malfunction indicator light may activate.

If you’re looking to diagnose or fix P0622 on your own, make sure you have a comprehensive understanding of automotive charging systems. You can read more about these systems in our in-depth technical discussion about charging and alternators.

Note: The definition of code P0622 may differ according to the vehicle manufacturer. Check the right repair manual or repair database for the exact code definition.

What are the Possible Causes of the P0622 Code?

• Faulty alternator
• Faulty battery
• Faulty powertrain control module
• Problem with the alternator’s wiring

What are the Common Symptoms of the P0622 Code?

• Engine fails to start
• Engine stalls
• Battery warning light

How to Diagnose the P0622 Code

A DTC P0622 is a generic trouble code that may be logged in vehicles from different auto manufacturers. These vehicles can share seemingly identical triggers and symptoms. However, the exact process for diagnosing and repairing your vehicle can vary between various makes and models.

If you don’t think you can run diagnostic tests on your vehicle, it’s a good idea to bring your ride to a professional mechanic. Otherwise, you may go ahead and diagnose the issue yourself. To help you get started, here is a video that may give you an idea of what the process might involve:

How to Fix the P0622 Code

Attempting to fix a P0622 code may become a frustrating task if you don’t have the right tools and know-how to test the PCM. In most cases, it’s best to leave the job to professionals.

For DIYers with advanced technical knowledge and hands-on experience who prefer to test and replace their vehicle’s faulty alternator on their own, it will be helpful to rely on the appropriate repair manual or an online repair database.

An In-Depth Look at Alternators and Charging

The alternator (also known as the generator) is responsible for maintaining battery charge while the engine is running. But the generator doesn’t just pump uncontrolled electricity into the battery and electrical system. The charge level is carefully controlled by some kind of voltage regulation system.

Charging in Older Generators

Older generators (those barrel-shaped ones that looked like an electric motor on late ‘50s vehicles) rectified their output through a commutator and brushes rather than using diodes, but the field strength on those units was still controlled by an electro-mechanical voltage regulator. The field was in the coils around the outside and the current was generated in the spinning armature that was attached to the pulley shaft.

Charging in Alternators

In an alternator, however, the electromagnetic field is created by feeding current through the windings in the spinning rotor, which is connected to the belt-driven pulley-shaft. The rotor spins within a “stator,” which is a trio of wires wound through a laminated metal core and connected to a series of diodes to “rectify” the AC current it creates, converting it to DC current, which is what the battery needs. Earlier alternators had an externally mounted voltage regulator. 

Later alternators had an internal voltage regulator that mounted within the alternator. The voltage regulator on these systems is activated or “turned on,” as it were, by the whisper of voltage passing through the instrument cluster’s battery or charge light bulb as the key is turned to the “on” position during starting.

Typically, within the instrument cluster, a small resistor is wired parallel with the bulb to prevent loss of charging system operation when the bulb blows. If the wire feeding the “L” terminal on the regulator is cut or shorted to ground, the regulator won’t allow the alternator to charge.

This electromagnetic field that saturates the rotor and creates electricity in the wire-wound stator is fed by a pair of spring-loaded sintered metal “brushes” sliding on rings mounted at the end of the rotor, and each end of the rotor’s electromagnetic winding is connected to one of these rings. To control the output of the alternator, the regulation system (whether it’s a voltage regulator or the ECM/PCM itself) will monitor system voltage and increase or decrease alternator output based on system voltage needs.

Charging and DTCs

The ECM/PCM knows system voltage by default, but voltage regulators must have a dedicated battery feed wire to monitor system (battery) voltage for proper charging system control. This same feed is used by some systems to feed the positive brush, and the field is controlled by switching the ground on the negative brush. It’s a duty cycle controlled field.

Chrysler has been controlling the alternator field with its onboard engine controller (ECM/PCM) since the mid 1980s. These days, just about every generator/alternator has its field controlled by the ECM/PCM. The ECM/PCM monitors its control over the field. This is what code P0622 and similar codes are about.

Newer systems also have a current measuring inductive pickup around the positive battery cable so the ECM/PCM can keep track of charging current.