Cruise Control Multi-Function Input "B" Circuit Range/Performance
P0591 indicates the engine control module detected a problem with the cruise control multifunction input B circuit, typically related to signal voltage being outside the expected range. This affects the cruise control system's ability to receive input signals and operate properly.
What You Might Notice
- Cruise control inoperative or unresponsive
- Cruise control light illuminated on dashboard
- Unable to set or maintain desired cruise control speed
- Abnormal vehicle speed fluctuations when cruise control is engaged
- Cruise control switches not responding to input
Most Common Causes
- 1
Cruise control switch malfunction
The cruise control stalk or button switch on the steering wheel may be faulty, stuck, or sending intermittent signals to the control module.
- 2
Wiring or connector issues
Corroded, damaged, or loose connectors in the cruise control circuit can cause signal degradation or open/short circuit conditions.
- 3
Steering wheel slip ring failure
The rotating contact assembly that transmits cruise control signals through the steering column may be worn or damaged.
- 4
Engine control module fault
Less commonly, the ECM itself may have a processing issue or input circuit failure preventing proper signal interpretation.
How to Diagnose It
- 1
Check Cruise control switch malfunction — The cruise control stalk or button switch on the steering wheel may be faulty, stuck, or sending intermittent signals to the control module.
- 2
Check Wiring or connector issues — Corroded, damaged, or loose connectors in the cruise control circuit can cause signal degradation or open/short circuit conditions.
- 3
Check Steering wheel slip ring failure — The rotating contact assembly that transmits cruise control signals through the steering column may be worn or damaged.
- 4
Check Engine control module fault — Less commonly, the ECM itself may have a processing issue or input circuit failure preventing proper signal interpretation.
How to Fix It
- 1
Test and replace cruise control switch
Use a multimeter to test the cruise control switch assembly for proper resistance and signal output. Replace the steering wheel control stalk if it fails testing.
- 2
Inspect and repair wiring harness
Visually inspect the cruise control wiring from the steering wheel through the steering column to the ECM. Clean or replace any corroded connectors and repair damaged wiring.
- 3
Replace steering wheel slip ring
If the rotating contact ring is damaged or worn, remove the steering wheel and steering column components to access and replace the slip ring assembly.
- 4
Clear code and road test
After repairs, use a diagnostic scanner to clear the fault code and perform a test drive to verify cruise control operation is restored.
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