CarScan
PID 44

Commanded equivalence ratio

The mixture ratio the unit is aiming for (lambda). One is exact stoichiometry; below one the unit asks for a richer mixture on purpose — acceleration, warm-up, protecting the catalyst — and above one it leans out to save fuel. This is the TARGET, not the result: what actually happened is shown by the oxygen sensors. A steady gap between target and fact is the most useful thing on this page.

What is normal

About 1.00 in ordinary driving. Noticeably lower means the unit is enriching on purpose, as it does under full load.

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

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.

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