The Engine Control Unit 
The Engine Control Unit (In Situ)
| Location | The ECU is located under the bonnet, behind the battery on the right-hand side (whilst facing the car). |
| 2021 Regulations Reference | 5.7.7 |
| Parts to Discard | None |
| Important Checks | Condition of the mounting plate, bolts and electrical connections/pins. |
Requirements
Do this as a priority, your ECU needs to posted and reprogrammed by Hybrid Tune so don’t delay.
When removed (using a permanent marker) write your name, car make and race number (if you have one) onto the back of the ECU. See this link for full instructions and details https://citycarcup.co.uk/ecu-instructions/
Suggested Disassembly Method (6 Steps)
Step 1. Disconnect the battery as described in the ‘battery removal’ lesson. Here a quick note and some reminders in the meantime. Disconnect the earth/negative (black) cable clamp first, when refitting replace the negative cable last, think ‘negative first off and last on’. Isolate the battery terminals if leaving the battery in place. Once ready remove the battery tray clamp (secured with 1 bolt) from the battery tray and lift out the battery.
1. Battery Removal 
2. Negative Terminal Removal 
3. Positive Terminal Removal 
4. Battery Removed
Step 2. Remove the top of the fuse box (lid) to gain better access and view of the ECU, then locate and remove the upper right and lower left bolts holding the fuse box in place for any given period.
1. Fuse Box Removal 
2. Fuse Box Removal 
3. Fuse Box Removal
Step 3. Prise the plastic securing clip as illustrated on the bottom right and lift the fuse box up and to the right. The fuse box will not move very much as it is still connected to the wiring loom, but this will give you better access to the ECU mounting frame located behind.
Fuse Box Removal 
2. Fuse Box Lifted Out
Step 4. This now reveals the ECU, note the cable ties securing the ECU harness connectors in place, remove these carefully with wire cutters. Now use a small screwdriver to pull/prise outwards the connected security clips on either side as illustrated.
1. ECU Wiring Harness Connections 
2. ECU Connectors (Pull Outwards)
Step 5. Remove the ECU wiring harness connections by lifting them carefully from the ECU.
ECU Wiring Harness Connections 
Removed ECU
Step 6. Having disconnected the ECU wiring harness conenctions you are now able to remove the 4 ECU mount bolts.
ECU Mount Bolts Removal