P0658
PowertrainActuator Supply Voltage A Circuit Low
Most people meet this one when the warning light comes on and the gearbox suddenly starts shifting like it's having a bad day, or the car drops into limp mode for no obvious reason. What's happening underneath is that the control module sends power out to various actuators (often transmission solenoids) through a supply circuit it calls 'A', and it's measuring less voltage on that circuit than it should be seeing. Low voltage there means the actuators can't do their job properly, so the module either flags the fault or pulls everything back to protect itself. It's usually a wiring or connection problem rather than the expensive bits having failed.
ⓘ Information only. This page provides general educational information about fault code P0658. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P0658 mean?
P0658 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Actuator Supply Voltage A Circuit Low.
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • Engine warning light on, sometimes with a transmission warning alongside it
- • Harsh, delayed, or erratic gear changes on automatics
- • Car dropping into limp mode, holding one gear and refusing to shift up
- • Loss of power or hesitation under acceleration
- • On some cars the light comes and goes with no real change in how it drives
- • Knock-on electrical oddities if the same supply feeds other actuators
Possible causes
Causes commonly associated with P0658, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Chafed, corroded, or broken wiring in the actuator supply circuit, the single most common cause. Harnesses that run near the gearbox or under the floor take a beating from heat, vibration, and road salt
- 2. A poor connection at a plug, think bent pins, spread terminals, or green corrosion creeping in where water has got in
- 3. Weak battery or a failing alternator dropping the whole system voltage low enough to trip the code, especially noticeable on cold starts
- 4. Blown fuse or a tired fusible link feeding that circuit
- 5. A failing solenoid or actuator pulling the supply voltage down because it's drawing wrong
- 6. The control module itself faulty internally, the least likely and the last thing you should suspect
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Read all stored codes and the freeze frame first. If you see transmission codes (P0700, P0750 family) sitting next to this one, that tells you which circuit and which actuator the module was worried about
- 2. Load-test the battery and check charging voltage at idle. A car sitting at 11 point something volts will throw all sorts of low-voltage codes, and there's no point chasing wiring until the supply itself is solid
- 3. Get a multimeter on the actuator supply terminals and check what's actually arriving, you want to see battery voltage, roughly 12 to 14V with the engine running. A reading well under that points straight at the wiring or a connection between the module and the actuator
- 4. Wiggle-test the connectors and harness while watching live data. A reading that jumps about when you move the loom has found your fault for you
- 5. Inspect fuses and any fusible link in that circuit, and pull the connectors apart to look for corrosion or pushed-back pins
- 6. If supply voltage is good all the way to the actuator and the wiring checks out, only then start looking at the actuator or the module, and check for manufacturer bulletins before condemning either
Common questions about P0658
What am I likely to pay to sort this out? +
It swings a lot depending on what's behind it. If it turns out to be a corroded connector or a chafed wire, an independent garage might charge an hour or two of labour to find and repair it, so call it £60 to £180. A failed solenoid pack on an automatic gearbox is more like £300 to £600 fitted depending on the car. Replacing a control module is the dear end, easily £600 and upward once you factor in the programming, which is why you don't want anyone jumping to that without proving it first. Independents are usually far better value than a main dealer for this sort of electrical diagnosis, and the diagnosis itself is most of the battle.
How do I work out which of these it actually is on my car? +
Voltage tells you nearly everything. Check the battery and charging system first, because a weak battery can throw this code with nothing else wrong. If the supply is healthy, put your meter on the actuator feed and compare what you measure against battery voltage. A big drop means the problem is in the wiring or a connection between the module and the actuator, and wiggling the loom while you watch the reading will usually find it. If voltage is fine all the way to the actuator and the code still sets, that's when an actuator or module fault becomes the suspect. Look at what other codes are stored too, since transmission codes alongside this one tell you exactly which circuit to chase.
Can I have a go at fixing this myself? +
The cheap, common fixes are within reach if you're handy. Cleaning up a corroded connector, replacing a blown fuse, or repairing a chafed wire are all doable on the driveway with basic tools and a multimeter. A weak battery or failing alternator is straightforward enough to sort yourself too. Where it gets beyond most home jobs is solenoid replacement inside an automatic gearbox, or anything involving the control module, since that needs proper diagnostic kit and often coding. Don't throw a new module at it on a hunch, that's an expensive way to discover the real fault was a £2 connector.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →