X Type 2005 AWD 3.0 Alternator was overcharging at 15 volts. Jaguar dealer said ECM was bad. Had foreign repair shop replace and program ECM but alternator still overcharging at 15 volts or wide open. Shop replaced alternator and battery less than a year ago and said both are good. They cannot figure out the problem. Any help would be appreciated.

 

Hi Ace had this problem last year with my x type. Except it isn't a problem, the x type alternator charges at a higher level than your average alternator. At about 15 volts to be precise, I only found this out after I had replaced the unit to discover that the new one was charging at 15 volts as well. That was when I spoke to Jaguar who put me right on the matter.
Regards Andy

 

Ace, there is some truth to what Andy said. When you first start the car, the alternator will artificially raise the voltage up to around 14.5 VDC and maintain it there til it thinks the battery has had the energy replaced that it used for starting the car. After that point, it will then drop the voltage back down to 13.7 VDC. With that being said, you also need to know what type of multimeter you have to know what numbers you need to consider good and bad. What I mean by this is that some multimeters take the average of the voltages it is seeing and display that. This is what most of the cheapy multimeters do. Then you have the higher end ones that actually figure out the RMS value (which may actually be slightly less than what the averaging style multimeter says). A higher end multimeter will tell you that in a normal state, the alternator will output 13.7 VDC, where the averaging style multimeter will read around 14.3 VDC. Save wire, same electrical signal, but 2 different indications. So, this may also play into your "15 volts" indication.

The big thing I would be looking at is pulling out a multimeter and measuring the orange wire with a green stripe, using the multimeter. If it is up around 13-14 VDC, then you have an issue as that wire is somehow shorted to battery voltage. If it is down around say 7-8 VDC, then this is the car artificially raising the voltage to recharge the battery. Please keep in mind that these voltages are based on having everything electrical turned off except for the engine. By turning on various electrical loads, you can cause the voltage on the orange/green wire to go up as the computer saw the voltage drop some and now has to apply a larger voltage to the alternator to make the output where the computer wants it to be.