The engine management light (EML / MIL) covers thousands of possible faults. Here are the 10 we actually see most weeks.
1 — O2 / lambda sensor
By far the most common EML trigger. Sensor ageing means slow response → fault code. £80 part, 30-minute fix.
2 — MAF (mass airflow) sensor
Contamination from oil-soaked panel filters. Symptoms: poor MPG, hesitation, EML.
3 — EGR valve
Soot-clogged or electrically failed. Limp mode common.
4 — DPF differential pressure sensor
Cheap part, expensive misdiagnosis if you replace the DPF instead.
5 — Glow plugs (diesel)
Trigger EML when one fails. Causes hard cold-start.
6 — Misfire / coil pack (petrol)
Lumpy idle + EML. Pull plug 1, swap with plug 4, see if the code follows the coil.
7 — Boost pressure / MAP sensor
Underboost or overboost codes. Often a split boost hose, not a sensor.
8 — Turbo actuator
VNT vanes sticking. Sometimes cleanable, sometimes a new actuator.
9 — AdBlue / NOx system
Diesel only. See our AdBlue faults guide.
10 — Catalytic converter efficiency
Last resort diagnosis — usually means upstream O2 or fuel-trim fault, not actually a dead cat.