Couple months ago I started getting a low battery. Please start engine light. After a few more times of driving, I then got a charging fault code. My cheap handheld scanner picked up no codes.
I remove the alternator and had it tested, but was not present during the testing, but was told that it was in good shape, voltage regulator parameters, diode, pattern, etc. etc. Reinstalled the alternator and several threads suggested a battery. Battery was only two years old checked the fusible link from the BMS module to the positive battery cable.. Had continuity. Being the BMS module was inexpensive I replaced it. Since I had battery disconnected drove for 45 miles without incident, but as I pulled into my garage, low battery, please start engine and charging system fault code showed up. I have been retired from the automotive repair field now for 32 years and what I was used to is no longer an easy step-by-step process. I’m wondering if anyone can tell me how to energize the alternator while it’s on the car to make sure that the test was that was done was correct.

 

As a starter, did you check the resting voltage of the battery which must be 12.6 volts minimum? Regardless of the age of the battery, it could be bad, These cars are super sensitive to low battery voltage.

 

actually, I did replace the two year-old battery. After my drive of 45 miles yesterday of course the battery was low. I have it on charge overnight and will test the resting voltage after the battery is fully charged.

 

Start by resetting the battery monitor system using SDD if you have replaced the battery, that will clear the message. Right now the car still assumes the remaining capacity of the battery is low, it does not know you physically replaced it, so it's charging it like an old depleted battery - slowly- and may not bring it up well.

As far as the alternator testing, if the car is running without a red "charging system fault" warning, it's working. Testing with the hood open will force the alternator on, the dynamic charging will not limit the alternator output with the hood open or when performing tests via SDD. It's a LIN controlled alternator, there is no way to bench test it, needs the PCM to work right.

 

Thank you for your response. It is much appreciated. If the BMS sensor is sensing a low battery would it not be telling the alternator to put out a higher voltage to charge the battery?
I only have a cheap handheld code reader. When I sold my repair shop after 91 years all of the good equipment went with the new owner. Do not think my reader is capable of resetting a Jaguar BMS sensor. I am presently charging the battery at a 12 V low amperage rate. I will test the resting voltage of the new battery when it comes off charge.

 

The real key is what Freddy J posted. After the car has sat all night what is the voltage? JLR wants 12.6 VDC minimum. Not after charging the battery but after sitting all night without a charger on it. Can you post what your car reads?

It does not matter how old or new the battery is. I would forget messing with the alternator unless you have codes pointing to that. Also be aware that if you do swap the alternator it is far better to get your OEM one rebuilt as many have had additional problems after replacing the entire alternator.
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Thank you for your response. Yes I’ve seen several threads that have mentioned the minimum voltage of 12.6.
I just finished charging the battery. Battery voltage reads 13.25V. I started the car turned the lights on and ran it for five minutes trying to take the surface charge off of it and after the battery voltage red 12.7. I will let the car sit for some hours and retest and then post what that voltage is. While the car was running, I put my volt meter on the battery post and with lights on and car running it only read 12.15 V someone mentioned earlier about opening the hood and somehow that tricks the charging system to start putting out, but I have no charging voltage at the battery.

 

Your code reader will not reset the BMS, but most decent generic scan tools can. You should have 13+ volts at the jump point when running. What are the voltage values at the big wire and small LIN wire on the generator when running?

 

When you say jump point do you mean where you would jumpstart the car from under the hood?
The plug connector on the alternator is too wire. Do you know by chance what color the LIN wire?
It’s been a couple days since I was underneath the car, but I presume I would have to cut some of the casing off of the wire to be able to prove it.

 

After charging the battery this morning. I ran the car for about five minutes with the headlights on to take the surface charge off of the battery. And it’s been about five hours since. battery voltage key off 12.75 at the jump port 12.74.
With Engine running at the battery post of the alternator 12.41 and at the jump port 12.42. Tried probing the back of the plug for the Lin wire. But got no reading. Do not know whether my probe made contact. Will remove some of the outside casing of that wire to verify, however, it’s 95° in my garage and with the engine running it is a tad bit uncomfortable, fishing, my hands up behind the altar to take those measurements. as the weather cools off tonight, I will probe the Lynn wire and paste post my findings.

 

According to topix, the small 2 wire connector only has one pin used, it's a blue with brown stripe wire for the LIN. it should be on pin 1 of that connector, if it's not that could be an issue.

 

Yes, after crawling back under the car today in this heat, although I saw two pins when the alternator was off, there is only one wire and it is blue. Too far up inside to see whether it had a brown tracer. As I said in my previous text, I will head back out tonight to test that wire for voltage since my voltmeter probe did not pick up any voltage at that blue wire, I will strip a section of it down to the wire inside and retest.

 

Good evening, the following are the voltage tests you asked for;

Ignition off.
Batt. 12.82
Jump port. 12.76V
Alt 12.77V
LIN. 7.95-8.0V

ignition on;
Batt. 12.50
Jump port. 12.50
Alt. 12.50
LIN. 7.90

Engine running;
Batt. 12.36
Jump port. 12.32
Alt. 12.35
LIN. 7.10

 

Without looking at the actual LIN data with a scope and confirming, I would assume that's a good reading. So your alternator should be charging but isn't. Engine ground strap is good right? Should be off the motor mount support arm on the right side to the frame. If so, I'd assume you actually have a bad alternator.