What is an ECU remap? Stages, gains, risks and insurance
How it works
Manufacturers calibrate one engine for every market, fuel quality and driver, then leave headroom under it. A remap reads the file from the ECU through the OBD port, modifies the maps that govern boost, fuelling and timing, and writes it back. On most cars built since about 2010 the whole job is done through the diagnostic socket in under two hours. Some newer ECUs are locked and have to be opened on the bench.
Stage 1 and Stage 2
Stage 1 is software on a standard car. It is the most common remap and gives most of the available gain. Stage 2 assumes hardware that lets the engine breathe and run cooler: a larger intercooler, a freer intake, a sports catalyst or downpipe. The map is then written to use it. Stage 2 gains are bigger but so is the stress on the clutch, turbo and drivetrain.
Typical gains
| Engine | Stage 1 gain | Why |
|---|---|---|
| Turbo diesel | 20 to 35 percent | Boost and injection timing have the most headroom |
| Turbo petrol | 15 to 30 percent | Boost and ignition timing, fuel quality matters |
| Naturally aspirated petrol | 5 to 10 percent | Timing and fuelling only, no boost to raise |
The remap database holds the published figures for over 2,000 UK engines, with a risk rating for each.
The risks
- Clutch. The first thing to complain on a diesel with a big torque gain, especially a dual-mass flywheel car with high mileage.
- Turbo and intercooler. More boost means more heat. A tired turbo will not thank a remap.
- Bad maps. The quality of the file is everything. A generic file with the torque limiters removed is how engines get damaged.
- Emissions deletes. Removing the DPF or EGR is illegal for road use and an MOT failure. A proper remap leaves them alone.
Warranty, insurance and MOT
A remap can be detected by a dealer, and the manufacturer can refuse a warranty claim on components it affects. On a car under warranty, most people wait. For insurance it is a modification and must be declared; most mainstream insurers accept a declared Stage 1 with an adjustment, and failing to declare it can void the policy. The MOT does not read the calibration, so a remap has no effect on the test provided the emissions equipment is intact.
Questions people ask
Can a remap be reversed?
Yes. A reputable tuner saves the original file before writing the new one and can put it back. Keep a copy of your original file.
Will a remap improve fuel economy?
Often a little on a diesel, because the extra torque means fewer gear changes and lower revs at cruise. Driven hard, it will use more.
How much does a remap cost?
A Stage 1 on a mainstream car is usually £250 to £450 in the UK. Bench work on a locked ECU, or Stage 2 with hardware, costs more. Use the quote form on any engine page in the remap database for a price.
Check a car now
Free DVLA and MOT check, plus the remap verdict for the engine actually fitted to your car.