What does the vent solenoid actually do?

It lets air back into the servo. Cruise control holds the throttle open using engine vacuum acting on a diaphragm, and while one solenoid admits that vacuum, the vent solenoid is what allows atmospheric air back in so the diaphragm can relax. That is how the system reduces speed, holds a steady speed accurately rather than only pulling harder, and releases when cancelled. Without control of the vent, the module has no way to modulate anything, which is why an electrical fault here stops cruise control from engaging in the first place.

Why does an open vent circuit stop the system engaging rather than making it stick?

Because the vent is designed to be open when it has no power. That is a deliberate fail-safe: with no electricity the servo is vented, the diaphragm relaxes and the throttle returns, so any loss of supply defaults to throttle closed rather than throttle held. A module that cannot control the vent therefore cannot hold a speed at all, and rather than engage a system it cannot modulate, it declines to engage. The failure direction here is toward the safe state by design, not by luck.

How do I test the vent solenoid without a specification figure?

Compare it against the vacuum solenoid on the same servo. The two coils sit inches apart on the same component and do broadly the same electrical job in opposite directions, which gives you a known-good reference built into the vehicle. If the vent coil reads infinite while the vacuum coil reads a sensible few tens of ohms, the vent winding has failed and no wiring repair will help. If both read much the same, the part is probably fine and the fault is in the vent circuit's wiring or connectors — a narrower and cheaper search. No other code in this block has that advantage.

Is it safe to drive, and could the throttle stick?

It is safe, and no. Cruise control will not engage, so the servo is not applying throttle at all — and the vent being unpowered is precisely the condition in which the servo is released. Beyond that, on essentially every vehicle fitted with this hardware the brake pedal releases the servo mechanically as well as cutting its power, and the throttle return spring closes the throttle by itself. The vent solenoid is how the system modulates speed, not how the vehicle is brought under control. Nothing else about how the car drives changes.

OBD-II trouble code

P0586: Cruise Control Vent Control Circuit/Open

The vent valve is deliberately built so that losing power releases the throttle. That fail-safe design is why an open vent circuit is a system that will not engage at all — and why you have a known-good coil sitting right next to it to compare against.

Low severityPowertrainCruise ControlDrivable short-term

Quick facts

System: Powertrain
Category: Cruise Control
Severity: Low severity
Drivable: Usually safe to drive short-term
Repair cost range: $80 – $700
DIY difficulty: Intermediate DIY

What does P0586 mean?

P0586 concerns the electrical circuit controlling the vent solenoid on a vacuum-operated cruise control servo, and the module has stored it because that circuit does not appear complete. Understanding what the vent solenoid is for makes the rest of the code straightforward, because its purpose is unusual among the components in this system.

A vacuum servo holds the throttle open using engine vacuum acting on a diaphragm. Applying vacuum is one solenoid's job. Getting rid of it is the other's. The vent solenoid lets atmospheric air back into the servo so the diaphragm can relax and the throttle can return, and this is what allows the system to reduce speed, hold a steady speed accurately, and release when cancelled.

The design detail that matters is that the vent path is arranged to be fail-safe. On these systems the vent is open when the solenoid is not energised, which means that any loss of power — a blown fuse, a disconnected plug, a broken wire, the ignition being switched off — releases the vacuum and returns the throttle. The system's default state with no electricity is throttle closed. This is deliberate, and it is the reason an electrical fault in this circuit produces a cruise control that simply will not engage rather than one that engages and misbehaves. The module cannot hold a speed if it cannot control the vent, so it declines to try.

The practical advantage this code has over the rest of the block is a comparison that is available nowhere else. The vacuum solenoid sits inches away on the same servo, is a coil of broadly similar construction, and is doing essentially the same electrical job in the opposite direction. That gives you a known-good reference without needing a specification figure or a second vehicle. Measure both coils. A vent coil reading infinite next to a healthy vacuum coil is a failed winding, established conclusively in one step. Two coils reading much the same is equally informative in the other direction: the part is probably fine and the fault is in the vent circuit's own wiring or connectors, which is a cheaper outcome and a narrower search.

One distinction is worth keeping clear, because it saves a wasted repair. The vent function can fail in two entirely different ways. This code covers the electrical one. The other is pneumatic: the vent usually breathes through a small filtered port, and a port blocked by debris or corrosion means air cannot get back in quickly even when the solenoid works perfectly. That produces a system that engages but releases sluggishly, which is a different complaint and does not set this code. So if you find P0586 stored and the driver also reports that cruise control was slow to let go before it stopped working altogether, you are most likely looking at two faults rather than one, and repairing only the wiring will leave the second one behind.

Finally, on safety: the driver has never been relying on this solenoid to stop the car. On essentially every vehicle fitted with this hardware, touching the brake pedal releases the servo mechanically as well as cutting its power, and the throttle return spring closes the throttle on its own. The vent solenoid is how the system modulates speed, not how the car is brought under control.

Common causes

Open winding inside the cruise control vent solenoid
Corroded or water-damaged vent solenoid connector in the engine bay
Broken conductor in the vent circuit between the module and the servo
Connector left partly mated or with a failed locking tab after unrelated work
Blown fuse or open supply feed shared by the servo solenoids
Chafed wiring where the servo loom crosses the bulkhead or a bracket
Failed servo assembly where the vent solenoid is integral and not separately available
Corrosion inside an integrated solenoid pack breaking the vent winding's connection

Symptoms

Cruise control will not engage at all
Cruise control engaging briefly and releasing immediately
Cruise control unable to hold a steady speed before failing completely
Set speed drifting downhill with no correction
No click from the servo when cruise control is set
Check engine light with the engine running entirely normally
Fault appearing after work in the engine bay near the servo
Cruise control that had become slow to release before it stopped working

Diagnostic steps

1.Locate both solenoids on the servo before testing either. A vacuum servo has two coils doing opposite jobs — one admits manifold vacuum to pull the throttle open, the other lets air back in to release it. This code belongs to the second. On some servos they are two separate items bolted to the canister; on others they are built into one assembly, and which arrangement you have decides whether this is a small part or a whole servo.
2.Use the other solenoid as your reference. This is the advantage this code has over every other one in the block: the vacuum solenoid sitting inches away is a coil of broadly similar construction on the same component, so you have a known-good comparison built into the vehicle. Measure both. If the vent coil reads infinite while the vacuum coil reads a sensible few tens of ohms, the vent coil has failed internally and you did not need a specification to establish it.
3.If both coils read the same and both look healthy, stop suspecting the part. Two matching readings on the same servo make an internal failure unlikely and point the diagnosis at the wiring or the connectors for the vent circuit specifically. That is a genuinely useful narrowing, and it comes free.
4.Check continuity of both vent circuit conductors from the module to the solenoid, and check for supply on the feed with the ignition on. The run is short, so this goes quickly. Give particular attention to the bulkhead crossing and to any point where the loom is clipped, since a broken conductor is most likely at a fixed point rather than in a free span.
5.Separate the electrical fault from the pneumatic one, because they produce different complaints and this code only covers the first. The vent path usually breathes through a small filtered port, and a port blocked by debris or corrosion gives a system that engages but is slow or reluctant to release — a mechanical problem that does not set this code. If you find P0586 stored and the driver also describes a sticky release, treat those as two separate faults rather than one.
6.Inspect the servo diaphragm and hose while the vent circuit is open, since the access is already there. A perished hose or a leaking diaphragm will prevent the system working after the vent wiring has been repaired, and discovering that on the road test costs another visit. Squeeze the hose along its length for hardening and splits, and check that the throttle cable or rod moves freely and is correctly adjusted.

Repair cost

$80 – $700

Diagnosis is cheap here at $80 to $150, because comparing the vent coil against the vacuum coil on the same servo gives a conclusive answer without needing a specification. A separately available vent solenoid is $30 to $150 for the part plus half an hour to an hour of labour. Repairing a broken conductor or a corroded connector is $60 to $200 with negligible parts cost. Where the solenoid is integral to the servo, the complete assembly is $120 to $600 plus one to three hours including throttle cable adjustment. Used and remanufactured servos are widely available for the older vehicles this hardware appears on, which can reduce the parts figure considerably.

Estimate your repair

Run the numbers for your vehicle

Open the Repair Cost Estimator with cruise control servo / actuator replacement preselected. Adjust labor rate and vehicle category to fit your situation.

Estimate your repair cost

DIY vs shop

This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.