UK Car Repair Questions? Ask a Mechanic for Answers ASAP
I'd 1st check that the main battery connections are on tight and they are corrosion free
Do the same for the engine / gearbox earth strap.Then follow the main positive lead back to the engine and down to the starter motor, and check the connection at this end as well.
There should also be a small wire to the motor which should have 12V when you're turning the ignition switch to crank. If the 12V isn't there, check back along this wire for damage to the insulation or corroded connections
This 12V feed comes directly from the ignition switch so this may be faulty and need replacing
Check the resistance of the main positive lead that runs down to the motor as anything more than a few ohms and it should be replaced
Don't forget totry a jump start from another car / battery as its possible the battery ispoor, if you have a voltmeter a healthy battery should read 12.7+V
also trysubstituting the battery for another as I've known a very flat battery to dragdown the system voltage too far even with jump cables
Ok if the ECU is faulty then you can get all sorts of odd issues 1st check if the ECU is getting power
if it is then check that the small ECU earth wires that run out of the engine bay wirign loom and are secured to the engine with ring terminals
if this is all OK then send the ECU off for testing
do you still need help?