UK, Jaguar S-type 3litre Petrol 1999.
The Check engine light recently came on in my car. It starts and drives absolutely fine, but to be on the safe side I decided to book the car in to a Mechanic to find out the cause, and also get a service (probably about due) and get front brake discs/pads replaced.
When I got the car back they told me that they haven't been able to clear the engine light fault, and admitted that they haven't spent much time (if any) diagnosing the cause, but they did give me the fault code -
P1633 "KAM POWER SUPPLY VOLTAGE TOO LOW"
So spend some time googling this, including my car's Make/Model. The googling is not very fruitful (A combination of not much info, or info that is difficult to understand) but there was a suggestion to check the main battery.
I have now checked the main battery and it seems to be fine (12.1 volts during engine off, lowest 10.22 during engine start, 13.7 engine running) so that rules that out.
As the car seems to work fine I assume the ECM is ok (one of the googled suggestions was possible ECM failure)
I paid a lot of money for the service+ brake replacement and still have the engine light, so I would like to find out as much as I can about it to either figure it out on my own, or if I have to give it to a mechanic again, have as much info as possible to reduce their man-hours (and therefore the cost to me) diagnosing and fixing it.
Supporting info: For a while now I've been disconnecting the main battery when not using the car (I only use it at weekends) because there's an alarm which goes off randomly which is related to backup anti-theft battery (The alarm is to indicate that this battery needs replacing) so by doing this I'm effectively clearing error codes from the ECM) I've been doing this for many months. The engine light only came on a few weeks ago.