Cruise Control Multi-Function Input Circuit Range/Performance
The P0591 code indicates that the Powertrain Control Module (PCM) has detected an abnormal voltage or signal from the cruise control multi-function switch or its circuit. This switch typically controls functions like set, resume, cancel, and coast. The issue is often due to a faulty switch, wiring problems, or a malfunctioning PCM. The circuit range/performance fault means the signal is out of expected parameters, not necessarily a complete open or short.
1. Most Common Causes
- Faulty or worn cruise control switch
- Short to ground or voltage in the 'B' input circuit wiring
- Loose, corroded, or poor terminal connections at the switch or PCM connector
- Damaged cruise control system relay or fuse
- Mechanical issue in the multifunction switch assembly (stuck or damaged buttons)
- Defective powertrain control module (PCM) (uncommon)
2. Symptoms You Will Notice
- Cruise control inoperative or intermittent
- Cruise control light on dash may flash or stay on
- Possible stored trouble codes related to cruise control
3. Step-by-Step Diagnosis
Step 1: Use a scan tool to verify the code and check for additional codes.
Step 2: Visually inspect the cruise control switch and wiring for damage or corrosion.
Step 3: Test the switch resistance and voltage with a multimeter according to manufacturer specs.
Step 4: Check for continuity and shorts in the circuit between the switch and PCM.
Step 5: If all else is fine, consider PCM reprogramming or replacement.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
Yes, it is generally safe to drive, but cruise control will not function properly. The vehicle's normal driving and braking are unaffected.
How much does it cost to fix?▼
Typically $50-$150 for diagnosis and switch replacement. PCM replacement can be more expensive.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.