Last year, the ECU light appeared on the dash of Mother Dearest's 2000 Xsara HDI. A trip to Citroen revealed a "Low Voltage" fault code and an "Engine Immobiliser" fault code. The Citroen mechanic cleared the faults for the princely sum of £50 and said to return the car if it happened again. How's that for diagnostics?
I have the engineer's sheet, which says faults were cross-checked with the airbag ECU and interior ECU and no other faults were logged.Anyhoo, the Old Man told me he'd used the car to jump-start his tractor, without the engine running. We assumed that the voltage drop was probably caused by jumping the tractor, and thought no more of it. However, a few weeks later, the light came back on.
It's been on ever since, and hasn't caused any problems.
HOWEVER, yesterday it wouldn't start. I tried several times, it would turn over and over, but not fire. Then, 2 minutes later, it started no problems. When I arrived at my destination, the doors wouldn't lock off the keyfob.
NOW... Here's where my confused and drink-addled brain starts spinning out all sorts of theories. Here is my best theory:
Someone tells me that the Xsara has a transponder in the keyfob which tells the car when it can start. I'm guessing if the keyfob battery goes flat then the engine won't start, because the transponder can't send a signal to the car. This would also explain why the doors wouldn't lock when I reached my destination.
I'm also thinking, if the transponder has any sense, it will tell the car when the keyfob battery is going flat. This could be recorded as an ECU fault re: low voltage and immobiliser fault. In theory, any sensible Citroen technician can recognise this, replace the keyfob battery, and charge £50 for resetting the fault code (and not kick the owner out saying "bring it back if it happens again").
The only uncertain part of this theory is: How come the car starts fine with the master key, if the master key doesn't have a battery in it? I tried yesterday, with the remote fob safely locked in the house 40 yards away, and it started fine.
Please feel free to shoot my theory down in flames and offer an alternative.
Finally, if I replace my keyfob battery today, how likely am I to find someone to reset the ECU fault codes FOC so that I can prove it's been fixed?
