P0657

What it means

P0657 is the generic code for an open circuit or fault in the actuator supply voltage 'A' circuit. The engine control unit monitors the supply voltage it provides to certain actuators, such as throttle, fuel injection, or other output drivers, and sets the code when that voltage is missing or outside the expected range. Which actuators are on circuit 'A' depends on the make, model and engine.

Symptoms

• Engine warning light on
• Engine cranks but fails to start, or starts and stalls
• Reduced power or limp mode
• Rough running or misfires
• Poor or erratic throttle response
• Other actuator or driver-related codes stored at the same time

Possible causes

• Blown fuse or faulty relay in the actuator supply feedlikely
• Open circuit, chafed wire or high resistance in the supply wiringlikely
• Corroded, loose or damaged connector terminals at the control unit or actuatorslikely
• Poor earth connection or low system voltage from a weak battery or charging faultpossible
• Shorted or failing actuator pulling down the shared supply and blowing the fusepossible
• Internal fault in the engine control unit's supply driverrare

How to diagnose

1. Read all stored codes and freeze frame data, noting any other actuator or voltage codes and the conditions when the fault set.
2. Check battery condition and charging voltage, since low or unstable voltage can trigger this code.
3. Consult the manufacturer's wiring diagram to identify which fuses, relays and actuators are on supply circuit A for this model and engine.
4. Inspect the relevant fuses and relay, and check for voltage at both sides of the fuse with the ignition on.
5. Visually inspect the wiring harness and connectors for chafing, water ingress, corrosion and pushed-out pins.
6. Voltage drop test the supply and earth circuits under load, and check continuity from the supply source to the control unit.
7. Unplug suspect actuators one at a time to see whether a short is pulling the supply down, then test each actuator's resistance against specification.
8. If wiring and actuators test fine, check the control unit's power and earth feeds before considering the unit itself.

How to fix

• Replace the blown fuse or faulty relay, after finding and fixing the cause of the failure.
• Repair or replace damaged wiring and clean or renew corroded connector terminals.
• Restore poor earth connections and repair any charging or battery fault.
• Replace any shorted or failed actuator found during testing.
• Repair or replace the control unit only after all external causes are ruled out, with any required programming done to the manufacturer's procedure.

Can I keep driving?

Nearby codes

• P0656GenericFuel Level Output Circuit
• P0658GenericActuator Supply Voltage A Circuit Low