PID 5A%
Relative accelerator pedal position
Accelerator pedal position as a share of full travel. The same movement that PID 49 and PID 4A show, but scaled to a hundred per cent: handy on a graph when you do not want to think about volts or about which of the two sensors you are looking at. Zero with the pedal released and a hundred with it on the floor means the assembly is healthy.
What is normal
Zero with the pedal released, about a hundred per cent flat out.
These figures hold for most cars, but the maker has the last word: some engines run hotter or idle higher by design.
Step by stepUnstable idle — how to find the cause
How it feels behind the wheel
The same fault shows itself in different ways. Each sign below says what to look at in the live data.
Will not start in ParkIn P the starter is silent, but in N the car starts. Or the other way round. Sometimes every gear letter lights up at once; sometimes cruise control will not engage.The revs are capped and the car will not accelerateThe pedal is flat to the floor but the engine caps out around three thousand and goes no further. The car moves, but sluggishly, and overtaking is impossible. The check light is often on.Cruise control stopped engagingThe button clicks but cruise never takes the speed — or it drops out after a few seconds.
How to see it
In CarScan: the Live data tab, «Start polling». The app asks the car several times per second, draws a graph and remembers the highest and lowest value of the trip.