Engine swap

Q I’ve swapped the engine in my 2009 MINI One 1.4 for a secondhand unit. Having never done anything like this before, I’ve got the engine back in and it turns over, but there are no sign of it firing up. I don’t think I’m getting any fuel to the spark plugs and have the fault code ‘P0120 1/3 throttle pedal position sensor switch A circuit’. I’m a bit reluctant to start swapping other bits to test this as I’ve not touched the sensor while changing the engine and it was previously fine. I’ve tried to check that I’ve made all the connections correct.

Gerry O’connor

A Starting with the basics, I am assuming that the replacement engine was from a good source and that you can be sure that it was running without problems before fitting.

As you have not replaced the sensor, the most probable cause of the throttle

position sensor code being triggered is a fault in the wiring circuit. The engine loom would have been disconnected and reconnected during the engine replacement process and this may have resulted in a poor connection at some point. I would also ensure that all the earth connections to the engine have been correctly attached and the earth points are clean.

You have mentioned not getting any fuel to the spark plugs, but I am unsure if you mean you are getting no spark at the plugs or if you mean the

fuel is not entering the cylinder via the injectors. If the problem is related to fuel, you should check that the fuel pump is running when the engine is being cranked – if this is not the case, you may have an immobiliser problem. If the pump is working when the engine is cranked, the fault will be in the engine management electrics. It would be wise to systematically check the connections of the multi-plugs which have been disconnected and also any earth points on the engine. This is the most likely source of the problem.