Orange engine warning light on: causes, what to do and affected cars

The orange engine warning light (or emissions light) means the engine computer has stored a fault in the engine or its emissions system. It does not say which: only reading the fault codes with a diagnostic tool tells you whether it is a spark plug, an injector, the EGR valve, the particulate filter or just a sensor (CarVerif, Isuzu D-Max).

The most common causes

Ignition (petrol engines)

Coils or an ignition fault cause misfires and turn on the engine light (CarVerif, Audi A1 II). On some engines each cylinder has its own coil: if one fails, the engine runs much worse (Lancia Ypsilon III guide).

Injection (mostly diesels)

On the Dacia Duster 1.5 dCi, about 15% of owners surveyed by Fiches-auto report injection problems: jerking, loss of power or an engine light (CarVerif). Injector incidents with an engine light are also reported on the BMW X3 F25 (CarVerif).

The EGR valve and particulate filter

A clogged EGR valve turns on the engine light, with limp mode, black smoke and loss of power (CarVerif, Audi Q5 2.0 TDI). A blocked DPF does the same; on the BMW 118d, code P2452 (DPF differential pressure sensor) comes with the light and limp mode (CarVerif). See our guides to a clogged EGR valve and a blocked DPF.

Sensors and electronics

A faulty sensor is enough to turn on the light. On a BMW 2 Series Active Tourer, a leaking fuel temperature sensor let diesel run into the engine wiring, for a €5,000 repair (Fiches-auto). On the 1.2 PureTech, spurious engine lights are reported (CarVerif, Citroën C4 III).

What to do when the light comes on

1. Watch how the car behaves: misfires, loss of power, smoke or noise mean you should ease off and get to a garage quickly.
2. If the car drives normally, still book it in: the light reports a real fault, even if you cannot feel it yet.
3. Have the fault codes read before agreeing to replace a part.

Before buying a used car

An engine light on during the test drive is a reason to walk away in almost every buying guide (CarVerif, BMW 1 Series E87; CarVerif, Dacia Duster II). Be wary of a seller who started the car before you arrived (CarVerif, BMW 1 Series F20). See our guide to test-driving a used car.