P0591 code meaning
Cruise Control Multi-Function Input B Circuit Range/Performance
What P0591 means
Cruise control buttons form a resistor ladder on one or two signal lines, each button giving its own voltage window. FCA uses two lines with offset windows – signal 1 is input A, signal 2 input B – and both must report the same button; GM evaluates the ratio to the reference. Any fault locks out cruise control; CARB treats this as emission-neutral, and GM and Ford set these codes without warning lamp. P0591 means signal 2 is outside its window while a button is pressed – for on/off FCA expects 0.900 V and sets the code above 0.980 V, active only while the button is held. Usual cause is oxidation at the six-pin steering wheel connector; in the Jeep Wrangler JK recalls it indicates a faulty clockspring. GM does not use P0591.
P0591 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.5 to 2 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P0591
- Cruise control working sporadically or not at all
- Cruise control locked out
- No check engine light
Common causes of P0591
- Most likelyOxidised steering wheel connector at clockspring or column module
- Most likelyClockspring dirty or faulty
- PossibleButton block aged
- Less likelyColumn module or PCM
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Cruise control switchClockspringSwitch wiringBody control module
What each part of P0591 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 5 | Area: vehicle speed, idle control and auxiliary inputs. |
| 91 | The exact fault in that area. |
What to do next
- Note P0591 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0591
What does P0591 mean?
P0591 means "Cruise Control Multi-Function Input B Circuit Range/Performance". Cruise control buttons form a resistor ladder on one or two signal lines, each button giving its own voltage window. It is a generic code, so it means the same on every make.
Is it safe to drive with P0591?
P0591 does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will P0591 fail an emissions test?
P0591 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is P0591 to fix?
Difficulty: medium. A typical repair takes 0.5 to 2 hours of work. This is a job for a workshop.
Will P0591 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.