On Tuesday, March 15, 2016 at 7:08:34 AM UTC-4, Cursitor Doom wrote:

I wish. It's been replaced for over 9 months now and it's still the same
as the day it was fitted.
But this is really about trying to rescue the old one. They don't come
cheap!

Try this:

Re-install the new unit. Power up the electrical system, but DO NOT start the engine.

Here is the tricky part and be exceedingly careful: While powered up, disconnect the battery, NEGATIVE FIRST. Make sure when that clamp comes off the battery it does so cleanly and quickly. SHORT the positive clamp to the negative clamp immediately and hold for a minimum of 30 seconds. This is the functional equivalent of rebooting the ECU. Shut off the electrical system. Reinstall the battery. Attempt to start. Does this help?

Note: If you have any coded devices such as so-called 'infotainment' systems and such, you will have to re-code them. If you have a chip-based navigation system, remove the chip for this process. But, 3 times in 10, it works. Not bad odds if the alternative is landfill.

If you have a Bosch unit, this is far more likely to work than if you have a British-made unit.... getting back to that old joke: why do the British drink warm beer?

Peter Wieck
Melrose Park, PA