I have a charging issue with my vehicle, I've already replaced the alternator, battery module sensor and the battery and something is telling the car not to charge. It's possible it's an ECM. I have an '09 XF 4.2. didn't know what the protocol was, if I could swap with the same part number, can I buy a used one and have it reprogrammed or do I have to go back to the dealership? I've looked on motologix/ all data and I don't see anything that's definitive..

 

It's not the PCM (aka ECM). Look elsewhere.

If you do a swap, expect the car to go into anti-theft and completely immobilised. Don't do it...

 

Tell us about the alternator. Where do you get it from? Is it an OEM or an aftermarket new or rebuilt because there is a lot of history that says some aftermarket alternators don’t work in these cars. I don’t know why, but if you search the forum you’ll see what I’m talking about.

 

It was an OE Denso

 

If you still have the alternator that was removed, it may be best to have a local automotive electrical specialist overhaul it. Many replacement alternators do not work correctly when installed, and cause the charge warning on the instrument cluster to remain on.

Have you checked the output of the alternator with a voltmeter across the battery terminals with the engine running?

 

Yes I have. It'll work at 14.7 volts and then for some reason it'll stop charging and it'll go down to 12.2 volts and it'll stay there, then. For whatever reason, when I take off the negative terminal, it resets and then when I start the car immediately after putting the negative terminal back on the battery. It works again. Which makes me think that it was something telling the alternator not to charge. I've fitted a new battery, battery module sensor on the negative cable and I've used my scanner to tell the vehicle that it has a new battery.

 

xf 4.2 has an orphan alternator that works like the later 5.0, 1 wire linbus to the ecm. it's not like the old 3L V6 with the FR wire or the dumb alternators on the older V8s

BMS tells the CJB charge status and batt temp, CJB sets desired charging voltage, hands it over to the ECM which reduces or increases the field. go do the diag come back, and yes they need programming. configure new module with sdd

 

Yes you can swap the ecu for a used one but you have to reprogram it using sdd after fitting. At least that is my experience on a 5.0.
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