What is an ECU (Engine Control Unit)?
The computer that runs your engine — fuel, ignition, emissions, everything.
Simplified animation — not to scale.
In plain English
The ECU (also called the Engine Control Module or "the brain") is the main computer that runs your engine. It reads dozens of sensors thousands of times a second and adjusts fuel injection, ignition timing, turbo boost and emissions to keep the engine running smoothly and legally.
"Like the brain in your body — it doesn't move anything itself, but nothing happens correctly without it."
How it works
Sensors all over the engine (air flow, coolant temperature, oxygen, knock, crank position, throttle, etc.) feed live data to the ECU. The ECU compares those readings to its programmed "maps" and tells the injectors, coil packs and valves what to do — adapting instantly to load, temperature and altitude. When something goes wrong, it stores a diagnostic fault code (DTC) that a garage can read with a scan tool, and lights the engine warning light on the dashboard.
Signs of trouble
- ⚠Engine warning light (sometimes flashing)
- ⚠Sudden loss of power or "limp mode"
- ⚠Stalling, rough idle or refusal to start
- ⚠Higher fuel consumption with no obvious cause
- ⚠Multiple unrelated sensor fault codes appearing at once
£400–£1,200+ fitted and coded
Always get a written quote. Prices vary by car, region, and parts brand.