P0622Generic code

P0622 Code: Generator Field "F" Control Circuit Malfunction

The P0622 code means the computer found an electrical fault in the alternator field "F" control circuit. It can cause the battery to stop charging or to charge too much. Check the fuse, relay, connector and wiring before you replace the alternator.

Severity
High
Can I keep driving?
Yes, but with caution
Estimated cost
$30 to $700
Difficulty
Medium
System
Computer and Outputs
Applies to
All OBD2 vehicles

Updated Reviewed by Renzo Chacca

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What the P0622 code means

On many modern vehicles the computer controls how much the alternator charges. It sends a command signal (a field terminal or a LIN communication line) and gets a status signal back. That lets it adjust the charging voltage to the temperature, the electrical load and the condition of the battery.

The computer watches the control circuit from its own driver transistor. The P0622 code flags an electrical fault in that control circuit. Before you replace the component, check the fuse, relay, connector and wiring, which are the most common causes.

If communication with the alternator fails, it usually charges at a fixed safe voltage, or it stops charging and the battery light comes on. Always measure the charging voltage with the engine running. It is the quickest way to find out whether the alternator is charging.

Always start with the simplest checks: fuse, relay and connector. Then check power, ground and signal with the component connected (using back-probes) and, last, the continuity of each wire to the computer. Replace the component only when all of that checks out.

P0622 code symptoms

  • Check engine light or another warning light on.
  • The battery does not charge, or it overcharges.
  • Battery light on.
  • A battery that keeps going flat.
  • A fixed or abnormal charging voltage.

Likely causes of the P0622 code

  1. Damaged connector. Loose, broken or corroded.
  2. Blown or defective fuse or relay.
  3. Wiring cut or shorted between the component and the computer.
  4. Failed component. The coil, the motor or the internal electronics.

How to diagnose the P0622 code step by step

  1. Activate the component with the scan tool and check whether it responds.
  2. Check the fuse and relay. Measure the voltage on both sides of the fuse, and swap the relay with an identical one.
  3. Measure the supply at the connector. You should see battery voltage with the key on or when the component is activated.
  4. Measure the resistance of the component and compare it with the manual. Also check the insulation to ground.
  5. Check the control wire for continuity to the computer and for shorts.
  6. Measure the charging voltage with the engine running: 13.5 to 14.7 volts.
  7. Inspect the small connector on the alternator. It tends to corrode.

How to fix the P0622 code

  • Repair the connector, the wiring or the power supply.
  • Replace the alternator (computer controlled) if it does not respond even with correct power and command signals.
  • Clear the codes and verify the repair.

Technical reference data

  • Normal charging voltage: 13.5 to 14.7 volts (it varies on managed charging systems).
  • Reference values: check the manufacturer data for your vehicle.

Brand-specific notes

This code is common on several makes. The control method differs, so make sure you know which kind of alternator control your vehicle uses before you start testing.

P0622 on Ford

Very common on Ford, where the computer commands the alternator through a control terminal.

P0622 on GM

Also common on GM vehicles, which use the same kind of computer controlled charging.

P0622 on Volkswagen

Common on Volkswagen, where the alternator is commanded over a LIN line.

Frequently asked questions about P0622

Can I drive with a P0622 code?
With caution. If the alternator is not charging, the vehicle will run only until the battery goes flat, so keep trips short and head to a shop.
What does the alternator field circuit do?
On many modern vehicles the computer controls the alternator through its field terminal or a LIN line, and it gets a status signal back. That lets it adjust charging to the temperature, the load and the battery condition.
Do I always have to replace the alternator?
No. Check the fuses, relays, connectors and wiring first, because they are the most common cause.
How much does it cost to fix P0622?
As a rough guide, between $30 and $700. A fuse or connector repair is at the low end, and a new alternator is at the high end.
What does the P0622 code mean?
It is a generic OBD2 code that means the computer found an electrical fault in the alternator field control circuit. The battery may not charge or may charge too much.
What is the most common cause of P0622?
With a P0622 code, the usual culprit is a damaged connector, a blown fuse or a wiring fault. The small connector on the alternator corrodes often, so check it early.

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