P0591 — Cruise Control Multi-Function Input “B” Circuit Range/Performance #

Note: The code description may vary depending on the vehicle manufacturer. Always refer to your OEM (Original Equipment Manufacturer) documentation for precise terminology.

• Ford: Cruise Control Switch ‘B’ Circuit Range/Performance
• GM: Cruise Control Multi-Function Input “B” Range/Performance
• Hyundai/Kia: Cruise Control Switch Input “B” Circuit Malfunction
• Volkswagen: Cruise Control Input Signal “B” Out of Range

Summary of code P0591 #

P0591 indicates that the Engine Control Module (ECM) or Powertrain Control Module (PCM) has detected an abnormal signal from the Cruise Control Multi-Function Switch “B” circuit. The cruise control system allows you to maintain a set speed without keeping your foot on the accelerator, and the multi-function input is a set of commands (such as set, resume, cancel) sent through the switch. When the signal from input “B” falls outside the expected range or performance, the system disables cruise control to prevent unsafe operation. This code rarely causes driveability issues, but it often disables the cruise feature until resolved. Addressing this fault ensures safe and convenient cruise control operation.

Common symptoms for code P0591 #

When P0591 is present, you may notice certain changes in how your vehicle’s cruise control behaves. The most common symptoms are related to the cruise system’s operation, though other warning lights may also illuminate.

• Cruise control not engaging or operating inconsistently
• Check Engine Light (CEL) or Service Engine Soon lamp illuminated
• Cruise control indicator flashing or not illuminating at all
• Possible inability to set or maintain speed via cruise system
• Stored trouble code(s) in the ECM/PCM

Most probable causes for code P0591 #

The causes of P0591 typically relate to electrical faults within the cruise control switch circuit or its wiring. The most likely issues, in order of frequency, are:

1. Defective cruise control multi-function switch (worn contacts or internal failure)
2. Damaged or corroded wiring/connectors in the circuit between the switch and the PCM/ECM
3. Faulty clock spring (spiral cable in the steering wheel, especially if other steering wheel controls are problematic)
4. PCM/ECM software glitch or internal fault (rare)
5. Aftermarket electronic accessories interfering with cruise control wiring

Step-by-step diagnosis for code P0591 #

Diagnosing P0591 requires a systematic approach. Always prioritize safety by disconnecting the battery before removing steering wheel components. Use a scan tool and a digital multimeter (DMM) for accurate testing.

• 1. Read and record all trouble codes and freeze frame data with a scan tool. Clear codes and see if P0591 returns after a short drive.
• 2. Inspect cruise control switch operation: Test all switch positions for proper tactile feedback and visible damage.
• 3. Check wiring and connectors between the cruise control switch, clock spring, and PCM/ECM for signs of wear, corrosion, or loose connections.
• 4. Test the switch circuit with a DMM for continuity and proper resistance values according to OEM specs.
• 5. Check the clock spring if other steering wheel controls are erratic or inoperative.
• 6. Test the PCM/ECM inputs if all previous steps check out, or consult OEM diagnostic flowcharts for deeper ECM/PCM testing.

Possible repairs for code P0591 #

Once you’ve identified the root cause of P0591, the appropriate fix will usually involve one of the following actions:

• Replace the cruise control multi-function switch if it fails continuity or resistance tests
• Repair or replace damaged wiring/connectors as found during inspection
• Replace the clock spring if faulty or if other steering wheel controls are also inoperative
• Update or reflash the PCM/ECM if a known software issue exists (rare; check OEM service bulletins)
• Remove or re-route aftermarket electronic devices interfering with cruise circuits

Can you drive with code P0591? #

Yes, you can drive with code P0591, as it does not directly impact the vehicle’s core safety systems or driveability. However, cruise control will be disabled until the issue is resolved. If you rely heavily on cruise control for long trips, address the issue promptly. If you notice any additional warning lights or erratic behavior from other steering wheel controls, schedule repairs as soon as possible to avoid further complications.

Vehicles most affected by code P0591 #

While P0591 can appear on a wide range of vehicles, it is most commonly reported on models equipped with steering wheel-mounted cruise control switches. The following vehicles have shown a higher incidence of this code:

• Ford F-Series trucks (F-150, F-250, etc.)
• Chevrolet Silverado and GMC Sierra
• Hyundai Sonata and Elantra
• Kia Optima
• Volkswagen Jetta and Passat
• Toyota Camry and Corolla

Common mistakes & best practices for code P0591 #

When troubleshooting P0591, avoid some frequent pitfalls. Taking a methodical approach can save you time and money.

• Mistaking a faulty clock spring for a cruise switch or wiring fault—always test all steering wheel controls.
• Overlooking damaged connectors hidden beneath steering column trim or in the harness accordion boot.
• Skipping OEM wiring diagrams—always verify pinouts and expected resistance values.
• Neglecting a recent aftermarket installation that may have interfered with cruise control wiring.
• Not clearing codes after repair and confirming cruise control operation before returning the vehicle to service.

Quick FAQ for code P0591 #

Here are answers to some common questions related to P0591.

• Q: Can a bad cruise switch cause other steering wheel buttons to stop working?
  A: Usually no, but if the clock spring (steering wheel spiral cable) is faulty, it can affect multiple controls, including audio and airbag circuits.
• Q: Will clearing the code with a scan tool fix the problem?
  A: No, clearing the code may temporarily turn off the warning light, but the root cause must be repaired or P0591 will return.