Alternator and battery replacements

I replaced the alternator and batter in my 2004 Jaguar S-Type with off market bosch alternator. The battery light wont come off the dashboard. The autoshop is saying that is normal since we used a non jaguar brand alternator. Is this safe to still drive? They also said it is showing its getting the necessary 15.4 v when they test

This why I send the ORIGINAL alternator to my local rebuilder. She uses Toyota or Denso parts and the units always work properly.

My other alternative is a ‘good-used’ from a salvage yard.

Bosch is NOT the OE manufacturer of the alt. (Denso is)

You might have had a better chance with a DENSO unit.

I agree. The S-type alternator was customized by Jaguar with special circuits to work with the S-type’s ECU to control output. Non-Jag units don’t have these electronics.

If the alternator is constantly putting out 15.4v even when warmed up and running for a while, it’s likely to shorten your battery’s lifespan.

Also, with the battery light on all the time, you’ll have no way of knowing if something really goes wrong with the system, because you’ll be ignoring the light that is constantly lit up.

If you pick up a replacement alternator from some source, make sure they guarantee it is the proper Jaguar specific part. It’s common for a generic parts vendor to list a standard Denso alternator as “fits S-type” - it will fit, but that doesn’t mean it will work properly!

If this is a 4.2 V8 S-type, it’s a lot of labor and work to replace the alternator. So it’s worth the extra money to get the right unit. The OEM unit is rather expensive, so a rebuild is the more economical way to go (which is what I did.)


So, to clarify, does the S-type use a “smart alternator”?


In the sense that the charging voltage can be controlled based on differing conditions by the ECU, yes.

If I recall the service manual correctly, the 2.5/3L V6 motors switch from low to high (13.6 to 15.1), the diesel continuously variable between 13.6 to 15+v, and the 4.2L V8 variable between 14-15v, tapering off as the alternator warms up. Then when warm it sticks to around 13-14v.


Or does it just energize “smart circuits” of the ECU which monitor what the alternator is doing?

BP, HR, A1C, etc.