Actuator supply A is a high-side switch feeding several actuators together; its use differs by maker (Ford transmission solenoids, GM shared high-side driver, GM Europe 2.0 CDTI internal 5 V supply). P0657 is the open-circuit code; it is documented at Ford: the high-side switch of the 5R110W and 6R80 automatics feeds all shift solenoids, and the 2023 diesels split them into two supplies (P0657 and P2669), checked continuously. On a fault the solenoids are de-energised and the transmission falls back to a mechanical limp gear with maximum line pressure – harsh shifts and a single forward gear. Ford's 6.8 L V10 reports it with or without the lamp depending on the variant. GM does not use P0657 and reports opens together with ground faults under P0658.
Medium severity. Can I keep driving?If the car is running normally, drive in moderation to a repair shop. If it loses power or another warning appears, do not continue.
Symptoms
- Transmission limp mode (fixed gear)
- Harsh shifts, no upshift
- Check engine light (depending on the variant)
- Codes for individual shift solenoids
Most likely causes
- Open or connector fault at the transmission pass-through connector or wire to the valve body
- Damaged harness
- Internal high-side switch in the engine or transmission module
- Internal transmission harness
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: hard
- It can trigger limp mode.
- It affects emissions.
What each character of P0657 means
- P: Powertrain: engine and transmission
- 0: Generic code: same on every make
- 6: Control modules and outputs
- 57: Specific fault in that system
Frequently asked questions
Can I keep driving with code P0657?
If the car is running normally, drive in moderation to a repair shop. If it loses power or another warning appears, do not continue.
What causes code P0657?
The most common causes are: open or connector fault at the transmission pass-through connector or wire to the valve body; damaged harness; internal high-side switch in the engine or transmission module.
Related codes
- P0658Actuator Supply Voltage A Circuit Low
- P0659Actuator Supply Voltage A Circuit High
- P2669Actuator Supply Voltage B Circuit/Open
- P0750Shift Solenoid A
- P0973Shift Solenoid A Control Circuit Low
Sources
- law.cornell.edu: 13 CCR 1968.2
- newtonnet.co.uk: fordobd2012
- fordservicecontent.com: obd summary diesel 2023
- roushcleantech.com: Roush CleanTech Diagnostics Manual DA 8.5.18
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.