PID 07%

Long term fuel trim B1

Long term fuel trim, bank 1. The unit remembers what the short term trim (PID 06) keeps repeating and shifts the delivery for good. That is why the short term figure wanders around zero while this one sits still — and it is this one that shows how far the car has drifted from the factory setting. Plus ten or more points to an air leak or weak fuel delivery; minus ten or below points to a leaking injector or pressure above normal.

What is normal

The same meaning but accumulated: this is the one that shows an old, settled fault.

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

P0171System too lean (bank 1) — air leak or not enough fuel P0172System too rich (bank 1)

We have a detailed piece on thisLean and rich mixture: P2177, P2187, P2195 vs P0171

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.

P0171System too lean (bank 1) — air leak or not enough fuel P0172System too rich (bank 1)

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.

Hard to start when hotIt starts instantly from cold, but after a drive it cranks for a long time and catches reluctantly. Pressing the throttle sometimes helps.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.Slow to warm up, the heater blows coldThe temperature needle sits low for ages, the cabin stays cold, and on the motorway it gets worse. Consumption rises noticeably.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