P0591
UniversalCruise Control Multi-Function Input B Circuit Range/Performance
Low SeverityThis code indicates a problem with the electrical signal from the cruise control multi-function input switch or its circuit. It means the vehicle's computer is receiving a signal from the cruise control system that is outside the expected operational range or performing erratically, which will typically prevent the cruise control from engaging.
⚠️ Before You Begin (Safety First)
Always ensure the vehicle is turned off and the parking brake engaged before performing any diagnostic or repair work. If working with electrical components, disconnect the battery's negative terminal to prevent accidental shorts or injury. Consult your vehicle's service manual for specific procedures.
Common Symptoms
- Cruise control does not engage
- Cruise control disengages unexpectedly
- Check Engine Light (MIL) illuminated
- Intermittent cruise control functionality
Common Causes
- Faulty cruise control multi-function switch (Input B)
- Damaged or corroded wiring in the cruise control circuit
- Poor electrical connection at the switch or PCM
- Faulty Powertrain Control Module (PCM) (less common)
- Blown fuse related to the cruise control system
Frequently reported on: General/Universal
Diagnostic Steps
- Visually inspect the cruise control multi-function switch and its wiring for any obvious damage, frayed wires, or corrosion.
- Check for any blown fuses related to the cruise control system in your vehicle's fuse box, typically found under the hood or inside the cabin.
- Using a multimeter, test the continuity and resistance of the cruise control multi-function switch and its associated wiring according to your vehicle's service manual specifications.
- Ensure all electrical connectors to the cruise control switch and the PCM are clean, secure, and free from corrosion.
- Clear the code and retest the cruise control system after performing any repairs or adjustments.
👨🔧 When to Call a Professional
If you've checked the basic wiring and switch connections and the issue persists, or if you're uncomfortable with electrical diagnostics, it's best to consult a professional mechanic. They have specialized tools to accurately diagnose circuit issues.
Commonly Asked Questions
What does "Multi-Function Input B" refer to?
It typically refers to a specific input circuit within the cruise control switch or related steering wheel controls that sends signals to the engine computer.
Can I drive with a P0591 code?
Yes, generally you can drive the vehicle without issues, as the code only affects the cruise control system and not essential vehicle operation. However, it's best to address it to restore full functionality.
Is a P0591 always caused by the cruise control switch?
While a faulty cruise control switch is a common cause, the code can also be triggered by wiring issues, connector problems, or in rare cases, a PCM fault.
How do I test the cruise control multi-function switch?
You would typically use a multimeter to check for proper resistance changes or voltage signals at various switch positions, comparing them to specifications in your vehicle's service manual.
Can a blown fuse cause a P0591 code?
Yes, a blown fuse in the cruise control circuit can disrupt the input signal, leading to this code. Always check fuses first.