PID 09%

Long term fuel trim B2

Long term fuel trim, bank 2. It reads like bank 1 (PID 07), but it only means something next to it: on a healthy engine the two banks run almost level. Once they part, the fault is on one side — and this pair is what names the side. A shared cause, such as a clogged filter or a weak pump, moves BOTH banks at once; a local one, such as an air leak or an injector, moves only one.

What is normal

A difference of more than 10 % between the banks means the trouble is on one side of the engine, which narrows the search at once.

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

P0174System too lean (bank 2)P0175System too rich (bank 2)

We have a detailed piece on thisFuel trims: how to read them

Step by stepHow to find an air leak using fuel trims

Codes behind this reading

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

P0174System too lean (bank 2)P0175System too rich (bank 2)

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 engine stumblesThe engine runs unevenly, the car shakes at idle, the exhaust note stutters. On the move the pull sags and consumption rises.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.Fuel consumption has gone upYou refuel noticeably more often for the same driving. The lamp is usually off — the unit thinks it is coping.It stalls at idleAt the lights, or when you lift off, the engine dies. It usually restarts straight away.It smells of petrolA fuel smell in the cabin or around the parked car. Sometimes with the Check Engine lamp on.Smoke from the exhaustVisible smoke from the tailpipe. The colour is the clue: white, blue and black mean entirely different things.Check engine came on after refuellingYou filled up, drove a few kilometres, and the light came on. The car drives exactly as before.

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