Powertrain, generic · Vehicle speed, idle control and auxiliary inputs

P0591 Cruise Control Multi-Function Input B Circuit Range/Performance

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

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.

Likely causes

Oxidised steering wheel connector at clockspring or column module
Clockspring dirty or faulty
Button block aged
Column module or PCM

Symptoms

  • Cruise control working sporadically or not at all
  • Cruise control locked out
  • No check engine light

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€0–500
Time0.5–2 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

cruise control switchclockspringswitch wiringbody control module

Related codes

P0579P0589P0590P0592P0593P0585

References: static.nhtsa.gov, static.nhtsa.gov, static.nhtsa.gov.