CarScan
PID 45%

Relative throttle position

Throttle position as a share of full travel. The same as PID 11 but scaled to a hundred per cent: zero with the pedal released, a hundred with it on the floor. That makes it easier to read on a graph and to compare different cars whose sensors output different voltages. If it shows a few per cent rather than zero with the pedal released, the throttle is not closing fully — usually because of carbon around its edge.

What is normal

Zero with the pedal released. Anything else means the throttle is not returning all the way.

These figures hold for most cars, but the maker has the last word: some engines run hotter or idle higher by design.

Codes about this parameter

P0121Throttle position sensor A circuit range/performanceP0122Throttle position sensor A circuit low inputP0123Throttle position sensor A circuit high input

Codes behind this reading

If the value is out of range, the unit usually says so with one of these codes.

P0121Throttle position sensor A circuit range/performanceP0122Throttle position sensor A circuit low inputP0123Throttle position sensor A circuit high input

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.

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.Idle speed huntsThe tachometer needle wanders up and down with the car standing still: 1200, then 600. Sometimes the engine nearly stalls and picks up again.The car has lost powerThe car moves, but sluggishly: flooring the throttle changes nothing, the revs climb reluctantly. Often the lamp is on as well.It stalls at idleAt the lights, or when you lift off, the engine dies. It usually restarts straight away.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.

What the app does