OBD-II Code P0595 — What It Means & How to Fix It

What Does This Error Mean?

P0595 means the cruise control servo control circuit is reading a voltage that is too low. The PCM sends a control signal to the cruise control servo, and that signal should stay within a specific voltage range. When the voltage is consistently below the expected minimum, P0595 is stored. This usually points to a short to ground in the servo circuit or a servo that is drawing too much current. Cruise control will be disabled.

Affected Models

All vehicles 1996+
Common in GM SUVs and trucks
Common in Ford E-Series and F-Series vehicles
Common in Dodge Ram trucks
Common in any vehicle with a vacuum or electric cruise control servo

Common Causes

Short to ground in the servo control wire between the PCM and the servo
Faulty servo with an internal short pulling the control circuit low
Damaged wiring harness where insulation has worn through to bare metal
Corroded connector at the servo creating a low-resistance ground path
Failed PCM driver circuit outputting incorrect low voltage — uncommon but possible

How to Fix It

Check the cruise control fuse first. A short to ground often blows the fuse. If the fuse is blown, replace it and immediately unplug the servo connector before turning the key back on.

If the new fuse holds with the servo unplugged, the short is inside the servo. If it blows again, the short is somewhere in the wiring harness.
With the servo unplugged, use a multimeter to check resistance between the control wire and ground. A low resistance reading (close to zero ohms) confirms a short to ground in the harness.

A healthy open circuit should show very high resistance (infinite or close to it) when the servo is disconnected.
Inspect the harness from the servo back toward the PCM. Focus on areas where the harness passes through the firewall, near heat sources, and any points where it could rub against sharp metal edges.

A short caused by harness abrasion is one of the most common wiring faults in the engine bay.
If no harness damage is found, the servo itself is the most likely culprit. Replace the servo, clear the code, and retest cruise control function.

Install a new fuse of the correct amperage after replacing the servo. Never install a higher-rated fuse to compensate for a circuit fault.
After repair, clear all stored codes and take a short test drive on a highway to fully exercise the cruise control system at various speeds.

Confirm that coast, resume, accelerate, and cancel all function correctly before considering the repair complete.

When to Call a Professional

Tracking down a short to ground in the servo wiring requires a wiring diagram and a multimeter. If you are not comfortable with electrical diagnosis, a shop can locate and repair the short typically within 1 to 2 hours. Servo replacement runs $80 to $200 in parts, and short repair varies depending on where the damage is found.

Frequently Asked Questions

Why does a short to ground cause a 'low' code?

The control wire carries a voltage signal from the PCM to the servo. When that wire touches ground (the vehicle's metal frame), the voltage is pulled down to zero. The PCM sees the voltage as below its minimum threshold and stores a 'low' code.

Is P0595 more serious than P0594?

They are similar in severity — both disable cruise control. P0595 (low) often points to a short to ground, which can sometimes blow fuses or damage wiring. P0594 (general malfunction) is broader and may be caused by a simple open circuit or connector issue.

Can I fix a short to ground myself?

If the wire damage is visible and accessible, yes. Repair the damaged section with proper automotive-grade wiring repair tape or by splicing in a new section of wire. Hidden shorts inside the harness or inside the firewall are harder to access and may be better left to a professional.