I cannot find a cruise control servo on my car. Is it hidden?

It may simply not exist. A cruise servo is a separate device that physically pulls the throttle, and vehicles with an electronic throttle generally do not have one, because the module already controls throttle position and holding a set speed becomes a calculation rather than a mechanism. If there is no cable, chain or rod running from a canister or small motor to your throttle body, your vehicle almost certainly does not use a servo. In that case, check what your manufacturer specifically assigns to this code before buying anything, because the generic definition is describing hardware you do not have.

Why is the cruise control completely dead rather than just inaccurate?

Because there is no partial mode. A cruise control system pulls the throttle on your behalf, so the module is designed to treat any fault in the servo circuit as a reason to shut the whole feature down rather than operate it in a reduced state. On most vehicles it will also refuse to light the cruise indicator, so it looks as though the switch itself is dead. A completely inoperative system with this code stored is the normal presentation and does not mean multiple parts have failed.

It started right after I had the car serviced. Is that connected?

Possibly, but be careful with that reasoning on this code in particular. Cruise control is a feature people use on some journeys and not others, so it can be broken for weeks or months before anybody tries to use it. The fault very often gets noticed shortly after a service simply because the drive home from the garage was the first long run in a while. That said, a connector left unplugged during engine bay work is a genuine and common cause, so it is worth a two-minute look at the servo connector before you dismiss the coincidence entirely.

Can I test this in the driveway?

You can test the circuit but not the feature. The module normally will not attempt to drive the servo until the vehicle is above a minimum enable speed with the brake released and the system switched on, so a key-on check tells you nothing about whether cruise control works. Testing the wiring stationary is fine and is where the diagnosis happens, but confirming the repair requires clearing the code, driving above the enable speed, engaging cruise and watching it hold.

OBD-II trouble code

P0594: Cruise Control Servo Control Circuit/Open

An open is the one fault in the cruise servo block you can find with your eyes instead of a meter. It is also the one that has usually been there far longer than anyone realises, because nobody notices a broken cruise control until the day they want it.

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: $70 – $700
DIY difficulty: Intermediate DIY

What does P0594 mean?

P0594 is the module reporting that the control circuit to the cruise control servo is open or otherwise not behaving — the line it uses to command the servo does not present a complete, plausible path. It is the parent code of the group, which is why it is worded generally: it says the circuit is wrong without committing to a direction, where P0595 and P0596 name a low and a high reading respectively.

The servo is the muscle of an older cruise control system. The module decides what speed you asked for and how far the throttle needs to move to hold it, but something physical has to actually pull the throttle, and on the vehicles this code applies to that job belongs to a separate unit. On the most common design that unit is a vacuum canister with a rubber diaphragm inside and a short chain, cable or rod running to the throttle linkage; engine vacuum is metered into and out of the canister to pull the throttle open and let it close. On some designs it is a small electric motor driving a cable drum through a magnetic clutch, which achieves the same thing without vacuum.

That matters because it sets an expectation about the repair before you begin. This is not a sensor and it is not a software fault — it is a wire going to a mechanical device that lives in the engine bay. And it is worth confirming your vehicle has one at all. On a car with an electronic throttle, cruise control is generally not a separate mechanism: the module already controls throttle position electronically, so holding a set speed is a calculation rather than a component, and there is no servo to unplug. If you are looking under the bonnet of a modern vehicle for a cruise servo and cannot find one, that is not a failure of searching.

An open circuit is a real, physical separation, and that gives this code a quality none of the others in the block share: it is the one you have a decent chance of finding with a torch and your hands. There is a broken conductor, a terminal that has pushed out of its housing, a connector half-seated because its lock tab snapped, or a plug that was never reconnected. All of those are visible or findable by feel. The high-value inspection points are the servo connector itself, the point where the harness passes through the bulkhead, and the section of loom that flexes with the engine on its mounts — because copper does not usually break in the middle of a straight, supported run.

There is one habit worth breaking on this code specifically. Most diagnoses lean hard on the timeline: what happened just before the fault started, what was worked on, what changed. Here that question is nearly useless, because cruise control is a convenience feature that fails silently. A driver who mostly does short trips can go months without engaging it, so the honest answer to 'when did this start' is often 'the last time I tried to use it', which may be a season after the wire actually broke. Treating a recent oil change as suspicious because the fault was noticed the week after it is a good way to spend an afternoon on the wrong thing.

As for how the system behaves: it does not behave at all. Cruise control has no degraded mode. The module's response to a fault anywhere in this block is to disable the feature outright, refuse to arm, and in most cases refuse to illuminate the cruise indicator — which is the correct engineering decision, because a system that pulls the throttle on your behalf should either be trustworthy or absent. A completely dead cruise control with this code stored is the expected presentation, not evidence that several things have failed at once.

The vehicle drives normally in every other respect. Nothing in this circuit touches how the engine runs, and the throttle remains entirely under your foot. The practical cost of leaving it is the loss of a convenience feature and, on most vehicles, an illuminated check engine light — which matters mainly because an illuminated lamp fails an OBD-II emissions inspection regardless of what set it, so a convenience fault can end up on a deadline it did not deserve.

Common causes

Broken conductor in the servo control wire where the loom flexes with engine movement
Servo connector unseated, corroded or with a backed-out terminal
Harness chafed through where it crosses the bulkhead or a bracket edge
Failed cruise control servo with an internally open coil or motor winding
Connector left unplugged after unrelated engine bay work
Rodent damage to the loom running to the inner wing or firewall
Corroded ground for the cruise control servo circuit
Failed module output driver for the servo control channel
Aftermarket cruise control kit with a degraded splice or crimp
Water ingress into the servo connector from a blocked scuttle drain

Symptoms

Cruise control completely inoperative
Cruise indicator light refusing to illuminate when the system is switched on
System accepting the on command but never taking a set speed
Check engine light with no change in how the engine runs
Cruise working intermittently and cutting out on rough roads
Fault noticed long after the last work was done on the vehicle
Speed not held even briefly after pressing set
No other driveability complaint of any kind

Diagnostic steps

1.Establish first that your vehicle actually has a servo, because the answer decides whether there is any hardware to inspect. A cruise servo is a discrete unit that pulls the throttle on the driver's behalf: on older vehicles a vacuum canister with a diaphragm and a short chain, cable or rod to the throttle body, and on some designs a small electric motor with a magnetic clutch and a cable drum. On a vehicle with an electronic throttle there is frequently no servo at all, because cruise control is a software function running on the throttle the module already owns. If your car has no cable between anything and the throttle plate, stop and confirm what your manufacturer assigns to this code before you go shopping.
2.Find the servo and look at its connector before you test anything. On the vehicles that have one it lives in the engine bay on the inner wing, on the firewall or on a bracket near the throttle, which is to say it is bolted somewhere exposed to engine heat, road spray and whatever runs down the back of the bay in the rain. Unclip the connector, look inside both halves with a light, and look for green corrosion, a terminal that has backed out of its housing, or a locking tab that has been broken and left the plug half-seated.
3.Follow the loom from the connector with your hands rather than a meter. An open is a physical separation, and on this circuit it is normally in one of three places: at the connector, at the point where the harness crosses the bulkhead and gets pinched or chafed on a sharp edge, or at the section that flexes every time the engine rocks on its mounts. Flex each length gently along its run while watching for the outer sheath to hinge in one spot — that is where the copper has already broken inside.
4.Wiggle-test with the circuit live if the fault is intermittent. Back-probe the servo control terminal, set a meter to read the line, and disturb the harness section by section. A reading that jumps as you move one specific length locates the break far more reliably than a static continuity check, which will happily show a good path through two broken strands that happen to be touching.
5.Do not treat the age of the fault as a clue, because on this circuit it is not one. Cruise control is a feature people use on some journeys and not on others, so a wire that broke in March is routinely discovered in August. The 'what changed just before this started' question that opens most diagnoses returns nothing useful here, and answers like 'it has been fine, it just stopped working' should not steer you toward recent work.
6.Check whether the whole feature is dead or only partly dead before you condemn the servo. If the cruise light will not illuminate at all, if the set and resume buttons produce nothing, and if the system refuses to arm, that pattern points at the module's decision to shut the whole feature down rather than at one channel. The module does exactly that on any fault in this block — there is no reduced-function cruise control — so a completely dead system is the expected presentation and does not by itself mean more things are broken.
7.Verify the repair on the road, not in the driveway. The module will not usually attempt to drive the servo until the vehicle is above the minimum enable speed with the brake released and cruise switched on, so a bench test or a key-on check proves nothing about whether the feature works. Clear the code, drive above the enable speed, engage cruise, and confirm the system both takes the set command and holds speed.

Repair cost

$70 – $700

Diagnosis is $70 to $150. Most repairs on this code are wiring, and wiring is cheap in parts and variable in labour: repairing a broken conductor, replacing a corroded terminal or re-seating and sealing a connector runs $80 to $260 depending on where in the loom the break is and how much trim has to come out to reach it. A replacement cruise control servo is $60 to $420 for the part with half an hour to two hours of labour, and on the vehicles that still use one it is frequently a discontinued part — which makes a good used unit from a breaker a legitimate option here, since a servo carries no VIN coding and no programming. If the module's own output driver has failed, control module replacement and programming is $450 to $1,400, but that is the least common outcome on this code by a wide margin.

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.