P0593 – Cruise Control Multi-Function Input “B” Circuit High

P0593 is a diagnostic trouble code that points to a problem in your vehicle’s cruise control system, specifically an electrical issue in the cruise control multi-function switch “B” circuit. While it usually doesn’t leave you stranded, it can be annoying and may affect how safely and consistently your cruise control works. In this guide, you’ll learn what P0593 actually means, the most common causes, symptoms to watch for, how a mechanic would diagnose it, and what repairs typically cost so you can decide your next steps with confidence.

What Does P0593 Mean?

P0593 is defined as “Cruise Control Multi-Function Input ‘B’ Circuit High.” In plain language, your engine control unit (ECU) is seeing a higher-than-expected voltage on one of the cruise control switch circuits, usually the “B” circuit within the steering wheel or stalk switch assembly.

The “B” circuit usually corresponds to a specific function such as SET/COAST, RESUME/ACCEL, or sometimes CANCEL, depending on the manufacturer. A “circuit high” condition usually means an open circuit, short to power, or internal switch fault. The ECU detects this abnormal signal and disables cruise control as a safety measure, which triggers the check engine light and stores code P0593.

Quick Reference

• Code: P0593
• Definition: Cruise Control Multi-Function Input “B” Circuit High
• System: Cruise control / steering wheel switch circuit
• Severity: Low to moderate (comfort/safety feature affected)
• Typical Fixes: Switch replacement, wiring repair, connector cleaning

Real-World Example / Field Notes

In the shop, P0593 often shows up on vehicles where the owner says, “Cruise worked on and off for a while, then quit completely.” On a late-model Ford I worked on, the cruise buttons on the steering wheel felt slightly “mushy,” and the SET button didn’t always respond. Scanning the ECU showed P0593 and some intermittent cruise switch data in live readings. Pulling the airbag and wheel revealed a cracked ribbon cable in the clockspring and some green corrosion on the connector. Replacing the clockspring and cleaning the connector fixed the issue, and cruise control worked perfectly again.

Symptoms of P0593

• Check engine light on: MIL illuminated, sometimes with no other obvious drivability issues.
• Cruise control inoperative: Cruise will not set or engage at all.
• Intermittent cruise operation: Cruise may work sometimes, then drop out or fail to engage.
• Unresponsive buttons: One or more steering wheel or stalk cruise buttons do nothing when pressed.
• Erratic cruise behavior: Cruise may cancel unexpectedly when you hit bumps or turn the wheel.
• Other steering wheel switch issues: In some cases, audio or horn functions may also act up if the clockspring is involved.
• Stored cruise-related codes: P0593 may appear with other cruise or switch circuit codes.

Common Causes of P0593

Most Common Causes

• Faulty cruise control switch: Worn or internally shorted steering wheel or stalk-mounted cruise switch is the top cause.
• Damaged clockspring (spiral cable): The ribbon cable inside the steering column can crack or break, causing an open or high-voltage signal.
• Corroded or loose connectors: Moisture, drinks spilled on steering wheel controls, or age can corrode the switch connector and raise circuit resistance.
• Open or broken wiring: A cut, pinched, or broken wire between the switch and ECU can cause a “circuit high” condition.
• Poor ground connection: A weak or missing ground can make the ECU see abnormal voltage on the input “B” circuit.

Less Common Causes

• Short to power in the harness: Insulation rubbed through so the cruise signal wire touches a 12V feed.
• Internal ECU fault: Rare, but a failing ECU input channel can misread the switch signal as high.
• Aftermarket accessories: Poorly installed remote start, alarm, or steering wheel control interface spliced into the wrong wires.
• Water intrusion: Leaks into the steering column or dash area causing corrosion and intermittent high-resistance connections.
• Previous airbag/steering work: Incorrect clockspring installation or damaged wiring after airbag or steering wheel replacement.

Diagnosis: Step-by-Step Guide

To diagnose P0593 properly, you’ll want a decent scan tool (preferably one that can read live data and Mode $06), a digital multimeter, basic hand tools, and access to a wiring diagram for your specific vehicle. A service manual or OEM repair information is very helpful for pinouts and test values.

1. Confirm the code: Connect a scan tool, read all stored and pending codes, and note freeze-frame data. Clear the code and see if P0593 returns during a short test drive with cruise control attempted.
2. Check cruise operation: With the vehicle safely on the road, try turning cruise on, setting speed, resuming, and canceling. Note which buttons do not respond, as this helps identify which part of the switch (often “B” circuit) is affected.
3. Inspect steering wheel controls: Look for sticky, worn, or physically damaged buttons. If you’ve had drink spills or heavy wear, suspect the switch assembly.
4. Scan live data for switch status: Many scan tools show cruise switch inputs (ON/OFF, SET, RES, CANCEL). Press each button and watch the data. If the “B” function never changes state, the fault is likely in the switch, clockspring, or wiring.
5. Check fuses and power supply: Verify that all related fuses for cruise control, steering wheel controls, and the ECU are intact and have proper voltage on both sides.
6. Inspect connectors and wiring: Disconnect the cruise switch connector (often behind the airbag or steering wheel trim) and inspect for corrosion, bent pins, or loose terminals. Gently tug on wires to check for breaks under the insulation.
7. Test resistance/voltage of the switch circuit: With the battery disconnected and airbag precautions followed, remove the switch connector. Using a multimeter, measure resistance across the relevant terminals while pressing the “B” function button. Compare readings to the service manual specs. An open circuit or out-of-range value points to a bad switch.
8. Check the clockspring: If multiple steering wheel functions are intermittent (horn, audio controls, airbag light), test continuity through the clockspring. A broken ribbon cable will show open circuits on one or more channels.
9. Backprobe at ECU (advanced): If wiring and switch look good, backprobe the ECU connector and monitor the cruise “B” input while operating the switch. If the signal doesn’t change but is correct at the switch, the problem is in the harness or ECU.
10. Re-test after repairs: After replacing any component or repairing wiring, clear the code, road test, and verify cruise control works normally and P0593 does not return.

Pro tip: Always follow airbag safety procedures when working around the steering wheel. Disconnect the battery and wait the specified time before removing the airbag or clockspring to avoid accidental deployment.

Possible Fixes & Repair Costs

Most P0593 repairs are straightforward once you pinpoint the fault. Typical fixes include replacing the cruise control switch assembly, replacing a damaged clockspring, cleaning or tightening connectors, or repairing a broken wire in the steering column harness. In rare cases, an ECU repair or replacement may be needed.

At a typical shop, you might expect:

• Cruise control switch replacement: $150–$350 parts and labor, depending on whether it’s a simple stalk or integrated steering wheel buttons.
• Clockspring replacement: $250–$600, higher on vehicles with integrated steering angle sensors or more complex airbag systems.
• Wiring/connector repair: $100–$300, depending on how buried the harness is and how long diagnosis takes.
• ECU repair/replacement (rare): $500–$1,200+ including programming.

Costs vary with vehicle make, parts availability, labor rates in your area, and whether you use OEM or aftermarket components. The biggest factor is usually diagnostic time, especially if the issue is intermittent.

Can I Still Drive With P0593?

In most cases, you can still drive with P0593 without risking immediate engine damage. The main issue is that your cruise control may not work or may be disabled by the ECU. That means more driver fatigue on long trips and the inconvenience of manually maintaining speed. However, if the problem is related to a failing clockspring that also carries airbag wiring, you could have a potential safety concern if the airbag system is affected. If you notice an airbag light or other steering wheel control issues along with P0593, you should address it sooner rather than later.

What Happens If You Ignore P0593?

If you ignore P0593, you’ll likely just live without cruise control and deal with the check engine light staying on. Over time, corrosion or wiring damage can spread, possibly affecting other steering wheel functions or even the airbag system if the clockspring is involved. You also lose the ability to quickly notice new engine-related trouble codes because the light is already on, which can delay catching more serious issues.

Related Cruise Multi-function Codes

Compare nearby cruise multi-function trouble codes with similar definitions, fault patterns, and diagnostic paths.

• P0581 – Cruise Control Multi-Function Input “A” Circuit High
• P0577 – Cruise Control Input Circuit High
• P0596 – Cruise Control Servo Control Circuit High
• P0588 – Cruise Control Vent Control Circuit High
• P0584 – Cruise Control Vacuum Control Circuit High
• P0564 – Cruise Control Multi-Function Input “A” Circuit

Key Takeaways

• P0593 means the ECU sees a high-voltage fault on the cruise control multi-function switch “B” circuit.
• Common causes include a bad cruise switch, damaged clockspring, corroded connectors, or broken wiring.
• Symptoms are mainly cruise control not working or working intermittently, plus a check engine light.
• Diagnosis involves scan tool data, visual inspection, and multimeter testing of the switch and wiring.
• Repairs typically range from about $150 to $600 in most cases, depending on which component failed.
• You can usually still drive, but you should repair it promptly, especially if other steering wheel or airbag issues are present.

Vehicles Commonly Affected by P0593

P0593 can appear on many makes that use electronic cruise control and steering wheel-mounted switches. It’s fairly common on:

• Ford and Lincoln: F-150, Escape, Fusion, Explorer, and similar models with steering wheel cruise buttons.
• Chrysler, Dodge, and Jeep: Minivans, Ram trucks, and SUVs that use multifunction stalks or wheel switches.
• GM (Chevrolet, GMC, Buick, Cadillac): Trucks and SUVs with integrated steering wheel controls and clocksprings prone to wear.
• Hyundai and Kia: Sedans and crossovers with cruise buttons on the steering wheel.
• Volkswagen and other European brands: Models with multifunction stalks and complex steering column modules.

Any vehicle with electronic cruise control and a multi-function switch can set P0593 if the switch circuit “B” develops a high-voltage fault.

FAQ

Can I clear P0593 and keep driving without fixing it?

You can clear P0593 with a scan tool, and the code may stay away for a while if the fault is intermittent. But if the underlying issue is still there, it will eventually return. Driving is usually safe, but you’ll likely lose cruise control again, and the check engine light will come back.

Is P0593 related to the throttle body or engine power?

P0593 itself is not a throttle body or engine power code. It’s specific to the cruise control switch circuit. The ECU may limit cruise operation, but normal throttle and engine performance are usually unaffected unless other codes are present.

Can a bad clockspring cause P0593?

Yes. A failing clockspring is a common cause of P0593, especially if you also notice problems with the horn, audio controls, or an airbag warning light. The clockspring carries the cruise switch signals through the steering column, and a broken ribbon cable can create an open or high-voltage condition on the “B” circuit.

How do I know if the cruise switch or wiring is bad?

The best way is to use a scan tool to monitor cruise switch input data while pressing each button, then confirm with a multimeter at the switch connector. If the signal changes at the switch but not at the ECU, wiring or the clockspring is suspect. If the signal never changes at the switch, the switch itself is likely faulty.

Can I replace the cruise control switch myself?

On some vehicles, yes, especially if the switch is on a stalk and doesn’t require airbag removal. If it’s integrated into the steering wheel, you’ll need to safely remove the airbag and possibly deal with the clockspring. If you’re not comfortable following airbag safety procedures and torque specs, it’s safer to let a professional handle it.