OBD-II trouble code
P0659: Actuator Supply Voltage "A" Circuit High
The actuator power rail is reading higher than it should, and on a switched supply that usually means one thing: it is still live when the module told it to go off. The failure mode runs opposite to its siblings — devices stuck on rather than stuck off.
Quick facts
- System
- Powertrain
- Category
- PCM / Electronics
- Severity
- High severity
- Drivable
- No — stop driving until repaired
- Repair cost range
- $90 – $1,600
- DIY difficulty
- Advanced DIY
What does P0659 mean?
The other two members of this family describe a supply that is missing or weak. This one describes a supply that is present when it should not be, or above the voltage the module expects, and that difference changes almost everything about how the fault presents.
Start with what "high" means on a switched rail. The actuator supply is not permanently live — the module energises it, usually through a relay, and de-energises it when the devices on it should be inactive. If the module commands the rail off and still measures battery voltage on it, the supply is stuck live. The two mechanisms are a relay whose contacts have welded shut, which happens after years of switching an inductive load, and a short to battery voltage from an adjacent damaged wire in the same loom. Either way the module has lost the ability to switch off a group of coils and motors, and it reports the only thing it can see.
That is why the symptoms invert. A dead rail leaves actuators unable to move; a stuck-live rail leaves them unable to stop. Whichever devices sit on the rail run continuously — a purge valve that never seals so the engine runs rich at idle and stumbles after refuelling, an exhaust gas recirculation valve holding open so the engine idles roughly and hesitates off the line, a cooling fan that never switches off, glow plugs energised long past their duty cycle. The complaint that arrives at the counter is rarely "nothing works". It is usually a driveability fault, a flat battery overnight, or something audibly running with the key out.
The battery drain deserves its own mention because it is the most expensive consequence in ordinary use. A welded relay feeding solenoid coils can pull a steady current with the vehicle parked, and the owner replaces a perfectly good battery, then another one, before anyone connects the flat batteries to the stored code. If P0659 is present and the vehicle keeps going flat, those are the same fault and the parasitic draw test will land straight on this rail.
The other cause worth ruling out early is the simplest. The module compares the rail against an upper limit, so genuine overvoltage across the whole electrical system will trip it with the actuator circuit in perfect health. An alternator with a failed regulator pushing sixteen volts, or a jump-start or booster pack applied carelessly, does exactly that. Measuring charging voltage takes a minute and it settles the question before anyone opens a loom.
One further note specific to this code: a short to battery can damage the module's low-side driver, because those drivers are designed to sink current to ground and not to sit with battery voltage forced onto them. So a fault that began as a chafed wire can end as a module repair if it is left running. That is part of why this member of the family is rated as seriously as the other two despite the vehicle often still driving.
Common causes
- Relay contacts welded shut, leaving the actuator rail energised after the module commands it off
- Short to battery voltage from a chafed or heat-damaged wire routed alongside the supply circuit
- Charging system overvoltage from a failed alternator regulator, raising the whole system above the module's limit
- Damage from an incorrectly connected jump start or booster pack applied at the wrong polarity or voltage
- Aftermarket accessory wiring back-feeding voltage onto the actuator supply circuit
- Water or coolant intrusion into a connector bridging the supply to an adjacent powered pin
- Crushed loom behind an engine or against a bracket, shorting the rail to a permanently live conductor
- Failed high-side driver or supply stage inside the module holding the rail on
- Previous repair work that mis-pinned a connector and put battery voltage on the wrong terminal
Symptoms
- Actuators running continuously rather than not running at all
- Rough idle, stalling or a rich-running complaint from a purge or recirculation valve held open
- Cooling fans, pumps or solenoids audibly running with the ignition off
- Battery flat overnight or after a few days standing, often after the battery has already been replaced once
- Fuel smell or a failed evaporative emissions monitor from a vapour valve that never closes
- Check engine light on with codes from several devices sharing the rail
- Blown fuses recurring on the actuator supply feed
- Charging system warning or unusually bright lights if the underlying cause is overvoltage
Diagnostic steps
- 1.Measure charging voltage at idle and at raised engine speed first. System overvoltage sets this code with the actuator circuit in perfect condition, and it is quick to rule in or out.
- 2.Ask whether the vehicle has been jump started, boosted or had accessory wiring fitted recently, since both are direct routes to voltage on a circuit that should not have it.
- 3.Establish which actuators sit on the "A" rail for this vehicle, then check whether any of them are running when they should not be. A solenoid buzzing with the key out is the fault demonstrating itself.
- 4.Command the rail off with a scan tool and measure it. Battery voltage still present with the supply commanded off is the confirmation this code needs.
- 5.Pull the supply relay and re-measure. Voltage that disappears with the relay removed points at welded contacts; voltage still present with the relay out means the rail is being fed from somewhere else.
- 6.If voltage persists with the relay out, look for a short to battery. Disconnect circuits in sections and inspect the loom where it passes brackets, hot exhaust components or anywhere a previous repair was made.
- 7.Perform a parasitic draw test if the vehicle has been going flat. A stuck-live actuator rail is a steady, easily measurable draw and confirms the two complaints are one fault.
- 8.Inspect the module's connector for pushed-back, bridged or corroded pins before condemning the module itself.
- 9.After repair, verify that the rail switches cleanly both ways — live when commanded on, at zero when commanded off — rather than only checking that the code has cleared.
Repair cost
$90 – $1,600
A welded relay is the single most common finding and the cheapest, at $60 to $200 with diagnosis, which is why it is worth pulling before anything else. Correcting a short to battery is $150 to $800, the range reflecting whether the damage is at an accessible connector or inside a loom that has to be opened along its length. An alternator or regulator replacement, where system overvoltage turned out to be the real cause, runs $350 to $1,000 and fixes the code along with everything else it was quietly damaging. Add a battery at $150 to $350 if the vehicle has been discharging overnight, since repeated deep discharge shortens its life whether or not it was the original problem. Module replacement and programming at $700 to $1,600 is the outcome when a short to battery has taken out the driver stage — which is a real risk of leaving this fault running, and an argument for fixing it promptly rather than living with it.
Estimate your repair
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Open the Repair Cost Estimator with engine main / powertrain relay replacement preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an advanced DIY job. It typically requires specialty tools, scan-tool access, lifting equipment, or careful sequencing to avoid causing new failures. Plan for extended downtime and have a backup vehicle. Most owners are better served by a shop that has done this repair before.