Drivable — worth looking into
Cruise control stopped engaging
The button clicks but cruise never takes the speed — or it drops out after a few seconds.
There is no danger, but the symptom will not go away by itself: it is the early stage of something that gets pricier.
What to look at in the live data
- The speed reading in the app while driving: if it sits at zero, cruise will never engage.
- Speed sensor faults — they usually knock out the speedometer and ABS as well.
- Brake pedal faults: cruise is cut by the pedal switch, and a stuck switch keeps it off permanently.
Common causes, cheapest first
- The speed sensor or its connector: the car does not know how fast it is going.
- The brake light switch: to the unit the pedal is «pressed» all the time, and cruise is blocked.
- A fault elsewhere that put the car into a protective mode: cruise is the first thing disabled there.
Codes that show up with this
P0500Vehicle speed sensor malfunctionP0501Vehicle speed sensor — reading out of rangeP0502Vehicle speed sensor — low signal
These parameters in the reference
Vehicle speedThrottle positionAccelerator pedal position DAccelerator pedal position ERelative accelerator pedal positionRelative throttle position
Lamps that may be on
Do it step by step
P0171 is not a random string but an address. We take it apart, sign by sign.Reading a fault code: the letter and four digits
A symptom is not a diagnosis. The same sign comes from a dozen different causes — the readings are what tell them apart, not the feeling.
How the app helps
CarScan shows exactly these readings live, remembers the highest and the lowest value of the trip, and puts them into a report you can hand to a mechanic.