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

Note: The wording for this Diagnostic Trouble Code (DTC) may differ depending on the vehicle manufacturer.

• Ford: Cruise Control Multi-Function Input “B” Circuit High
• Chrysler: Cruise Control Switch 2 Input Circuit High
• GM: Cruise Control Multi-Function Input “B” Circuit High Voltage

Summary of DTC P0593 #

P0593 is an OBD-II (On-Board Diagnostics) code that relates to the cruise control system. Specifically, it signals a high voltage condition detected by the engine control module (ECM) or powertrain control module (PCM) in the “B” circuit of the cruise control multi-function input. The cruise control multi-function input is a set of electrical signals from the steering wheel or stalk switches that manage cruise control actions like setting the speed, resuming, accelerating, or canceling. A high circuit condition often means an abnormal voltage is detected, typically due to an open circuit, wiring issue, or a faulty switch.

This code does not directly affect core engine or transmission functions, but it does impact the cruise control’s ability to operate safely and correctly. While not an immediate safety concern in most cases, it can be inconvenient or even hazardous if you rely heavily on cruise control for long drives.

Common Symptoms for DTC P0593 #

When P0593 is present, it typically disables the cruise control system or causes erratic behavior. You may notice one or more of the following symptoms:

• Cruise control inoperative
• Cruise control disengages unexpectedly
• Cruise control indicator light does not illuminate or flashes
• Warning lights on the dashboard (Check Engine or Service Vehicle Soon)
• Loss of certain steering wheel or stalk button functions related to cruise control

Probable Causes for DTC P0593 #

Several factors can trigger P0593, but some are more common than others. Understanding the likely origins helps streamline diagnostics:

1. Faulty cruise control switch or buttons (the most frequent cause)
2. Open or short-circuited wiring in the cruise control input circuit
3. Poor electrical connections at the control switch, clock spring (rotary electrical connector in the steering wheel), or harness
4. Malfunctioning clock spring (the device allowing electrical signals to pass from the steering wheel to the vehicle’s wiring)
5. Defective ECM/PCM (rare)

Step-by-Step Diagnostic for P0593 #

Proper diagnosis is essential to avoid unnecessary parts replacement. Here’s a logical stepwise approach for troubleshooting P0593:

1. Scan for additional codes: Look for related codes (especially those for cruise control or steering wheel controls).
2. Visually inspect: Check the cruise control switch, steering wheel buttons, and related connectors for damage, debris, or corrosion.
3. Test switch operation: With a scan tool (OEM level preferred), monitor the cruise control switch inputs while pressing each button.
4. Check clock spring function: If buttons do not register, test continuity through the clock spring.
5. Inspect wiring and connectors: Look for broken, pinched, or frayed wires in the steering column or under the dash.
6. Check for high voltage: With a digital multimeter, measure voltage at the “B” circuit. Compare readings against OEM specs.
7. Test ECM/PCM: If all else passes, verify the control module’s cruise input pin is functioning correctly (rarely needed).

Possible Repairs for DTC P0593 #

The best repair addresses the root cause found during diagnostics. Here are the most common fixes associated with P0593:

• Replace faulty cruise control switch or button assembly
• Repair or replace damaged cruise control wiring or connectors
• Replace defective clock spring in the steering wheel
• Clean corroded terminals or connections at the switch or harness plugs
• Replace ECM/PCM (only if proven faulty, which is rare)

Is It Safe to Drive with DTC P0593? #

Yes, you can generally drive with code P0593 present, but with limitations. The main risk is the unavailability of cruise control, which might be an inconvenience, especially on long highway journeys. However, if you notice other electrical issues (like airbag or horn malfunctions, which could indicate a clock spring problem), it is best to have it inspected promptly for safety.

Vehicles Most Commonly Affected by P0593 #

P0593 can be found across various automakers, especially those using similar cruise control switch architectures. The following vehicles are more frequently reported with this code (not exhaustive):

• Ford F-Series trucks (F-150, F-250, F-350)
• Chrysler 300, Dodge Charger, Dodge Ram
• Chevrolet Silverado, GMC Sierra
• Jeep Grand Cherokee, Jeep Wrangler
• Some Toyota and Honda models with steering wheel cruise controls

Common Mistakes & Best Practices for P0593 #

Misdiagnosis or overlooked steps can lead to wasted time and money. Here’s what to watch out for, and how to approach this DTC:

• Replacing the switch without checking wiring—always inspect for wiring or clock spring faults first.
• Ignoring secondary symptoms—other steering wheel controls not working may point to a clock spring issue.
• Skipping scan tool input tests—use an OEM-level scan tool to verify switch signal integrity.
• Not checking for Technical Service Bulletins (TSBs)—OEMs sometimes release fixes for known cruise control wiring or switch issues.

Quick FAQ for P0593 #

Got questions? Here are fast answers to the most common concerns:

• Can I fix P0593 myself?
  If you’re comfortable with basic electrical diagnostics and have access to a scan tool and multimeter, you can check switches and wiring. For clock spring or module replacement, professional assistance is recommended.
• Will clearing the code fix the problem?
  Clearing the DTC with a scan tool may turn off the warning temporarily, but if the root issue remains, the code will return as soon as the cruise control is used or tested.