The removal of the 720S ECU is fairly straightforward and can be accomplished with a basic set of hand tools and a set of Torx bits.
Torx bits, sockets, & tools needed:
17mm deepwell socket (for lug nuts)
Phillips head screwdriver
If you have any questions along the way please feel free to reach out to M-Engineering for help. Info@M-Engineering.us
Please disconnect the negative terminal from the battery before removing the ECU. Leave the battery disconnected as long as ECU is removed. For instructions on how to access the battery consult your owners manual.
1. The location of the ECU for the McLaren 720S is located behind the passenger’s side (Left-hand drive) or driver’s side (right-hand drive) wheel. The rear fender liner will need to be removed in order to access the ECU. The ECU can be fully removed in about 15 minutes by a seasoned tech or about 30-45 minutes by a hobbyist with basic hand tools and Torx bits.
2. We will not be covering how to remove raise the vehicle and remove the wheel. However, there are designated jack points under the vehicle and the lug nuts are generally 17mm unless the are modified. You may need your lug nut key if you have swapped to after market aftermarket lug nuts. If you are having difficulties with this step please consult your owner’s manual or consider taking the car to a specialist who can assist you.
3. The fender liner is split and we only need to remove the rear portion of the liner to access the ECU. Once the wheel has been removed you will begin by removing the two plastic Phillips head screws & retaining clips. Simply unscrew them and they will back out of their retainer. These plastic retainers hold the rear liner to the forward liner
4. Next you will want to remove the remaining six Torx bolts holding the fender liner in. We’ve noticed over the course of doing many of these ECU removals that the sizes change from car to car. They all tend to be T25 or T27 but the size placement isn’t uniform across all cars, however the mounting locations are. There are 6 total torx bolts holding the rear fender liner on. They are circled in red below and pretty straight forward to find. Just be sure to choose the appropriate size Torx bit.
5. Once all Torx are removed the rear fender liner should slide out fairly easily. If you are finding yourself having to put significant effort into pulling it out please double check all Torx are removed. The plastic retaining pieces, where the Phillips head screws were, may need a small bit of pressure to removed them from the rear fender liner.
6. With the rear fender liner removed you can now access the ECU. There are three Torx bolts remaining that are holding the ECU in along with the wiring harness. It is easiest to free the ECU before trying to disconnect the wiring harness. The three remaining Torx are circled in red.
7. With the ECU now free you can disconnect the connectors by simply pulling on the lever away from the connector. The lever moves a locking slide out which separates the ECU from wiring harness.
Installation is the opposite of removal. Please remember to keep the battery disconnected when the ECU is not installed otherwise some faults may appear after reassembly.