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

P0578 Cruise Control Multi-Function Input A Circuit Stuck

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

Cruise control buttons are almost always a resistor ladder on one or two signal lines, each button giving its own voltage; the module reading it (GM and Saab from about 2010: the body module; FCA: steering column module or PCM) sends the button state to the engine module over CAN. CARB names cruise control as the example of an emission-neutral diagnosis – it is simply switched off – so GM lists all these codes as type C and Ford as non-MIL: no warning lamp, the engine runs normally. P0578 means input A shows the same valid button voltage beyond a time limit – a button stuck. The principle matches GM's per-button codes (20 s or 89 s), here for the whole line A. No manufacturer document available to us uses this code. FCA's Jeep JK recall for the clockspring lists its own code P1593 for a stuck switch instead.

Likely causes

Button mechanically stuck
Moisture or dirt producing a constant value
Clockspring or connector

Symptoms

  • Cruise control reacting unexpectedly
  • Cruise control locked out
  • No check engine light, engine runs normally

Repair estimate

DifficultyMediumDIY possible
Parts and labour€40–400
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

P0579P0580P0581P0564P0590

References: static.nhtsa.gov, law.cornell.edu.