CarScan
PID 49%

Accelerator pedal position D

The first accelerator pedal position sensor. There are deliberately two of them — the second is PID 4A — and they duplicate each other: the unit keeps comparing the readings and drops into limp mode if they disagree. So what matters is not the number itself but whether the two sensors move together. Once they part, the car loses power and will not rev even with the pedal on the floor.

What is normal

The pedal is read by two sensors at once, and they must agree.

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

Codes behind this reading

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

P2122Accelerator pedal sensor D — low signalP2123Accelerator pedal sensor D — high signal

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.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