Need help with ECU and body processor
 

Hello guys,

I am still trying to resolve a condition where the battery, after it's initial charging sequence, drains very quickly. New alternator and battery test good and my mechanic has been doing testing on the wire from the ECU to the alternator.

My personal hunch at this point is that the problem is the ECU. Rain water was leaking inside my passenger side due to problems with the way the black windshield molding was fitted, and the first time my car totally shut down due to a flat battery was after a carwash, so i am thinking water damage. Weird thing is you would think a water damaged ECU would throw some codes, but non are showing.

Question is this: I know that the BODY Processor module is in the same vicinity as the ECU. Is the BODY PROCESSOR module involved in any way with how my alternator charges? It could be the culprit if it's water damaged.

Help please!

Anyone know is the body processor is involved in the alternator charging ?

Spike, the body processor module has nothing to do with the alternator. Apples and volvos different. The body processor module controls all the electronics inside the cab of the car. has nothing do do with how the motor works other than passing on information to the other systems as part of the CAN bus.

Thanks Chris. That helps a lot .

I will only buy a ECU in that case.

Spike
On mine the cowling under the windshield warped and rain water ran onto the pass. floor, so when I had my windshield replaced I had the tech use his super-duper adhesive to glue it to the bodies flange( grove was missing on the plastic cowling) and) and the windshield and it will never leak. If I need a new windshield it will cost me a new cowling because it's never going to survive being taken off BUT it doesn't leak.
If you do this, replace your cabin filter before you do because you won't have access to it afterwords, it is under that cowling and if it got wet it will mold and stink,just a FYI.

Hi Spike,

I sympathise with your woes and you will be aware of my lack of experience in this department but try this:

Re: Draining X Type Battery
Couple of extra points to be wary of when checking for quiescent battery drain in the X Type, as advised by Jaguar.

First, the battery drain should be measured with the vehicle in the double-locked, armed state (i.e. vehicle alarm fully armed), with all doors and other body apertures either closed or latched, so as to appear closed from an electrical point of view. The test should take place after the vehicle has entered shutdown mode. The time taken for this to occur after key-off is 30 minutes.

Note: When the vehicle is armed, the effect of the LED flashing is to cause a pulsation in the measured current drain.
In this case, either the time average current should be taken (using a meter with an averaging function) or the current
reading should be taken, ignoring the brief high current peaks.

The current drain after the initial shutdown period, should not exceed 30 mA.

Secondly, the preferred method of testing following an excessive current consumption figure is to use the clamp of the
ammeter around individual fuse box leads to the various suspected circuits to identify a potential cause, rather than
the old method of pulling fuses out, in a one after the other fashion.

The main reasons for using the current probe to determine which fuse box / circuit the drain is going through are:

1. Many modules take a considerable time to power down, every time their fuse is removed and refitted,
the quiescent drain figures will need 30 minutes to reset.
2. Sometimes the drain is caused by a module ‘holding on’ to something that has been switched off. Sometimes it is
only a relay winding that is activated. Pulling the fuse can allow this to ‘reset’ and the drain will be lost and
undiagnosed.

I stole it from Astromorg on Jaguarforum.co.uk

I hope you get fixed asap (as soon as possible) with little angst?
Regards, Stu :)

Thanks so much for all the information.

Right now it "looks" like the ECU is the problem but it's a huge ordeal to get another one programmed to the car. My mechanic claims he has a way to program it but it requires 2 keys. I only have one key. On my XJS I just plugged in a ECU from a close vin number and I was done :-(.

Good luck Spike, thanks for the update, I am sure you will win in the end!!
Stu :)

New ECU and still the same problem. Now going for another alternator. This is getting old

Spike, I would recommend if at all possible, seeing what the voltage is on the orange/green wire (Pin #3 on the small plug for the alternator). If you are getting 12 VDC (or whatever the battery voltage is), then that would pretty much confirm you have a bad alternator. If you are getting a very low voltage, then odds are you are looking at a broken wire between the ECU and the alternator. You can get a rough idea if the alternator is acting right or not by simply connecting a multimeter across the battery and watching the voltage (or put the instrument cluster in the diagnostic mode) and then going for a drive. Hopefully you will be able to see the car act up and you can then see what the voltage does. If it drops to say 12.4 VDC (or lower), then you know the alternator is not putting out anything. If you see it hovering at say 12.7-12.9 VDC, then you know that the alternator is right on the edge of being overloaded, but it is still outputting something. If you can watch the voltage bounce between say 12.4 VDC and 13.7 VDC, then that would pretty much confirm a bad wire between the ECU and the alternator (barring the wire between the alternator and starter being bad and opening intermittently on you).

Hope this helps to shed some light on things.

Thanks Chris.

My mechanic has tested the voltage in the manner described. It looks like the problem is the new alternator which stops charging the car as it gets hot.

I hope I can solve this soon. Going into 3rd week

Ok, second alternator, new ECU, new battery cables, and wiring thoroughly checked... car still will shut down after about 15 minutes with full load (a/c, lights and fogs on) at idle. Mechanic says that fan module is pulling more than what it should.

Help please!!! This car is driving me crazy

Thanks, sorry for the rant

Anyone have any ideas on this? My mechanic noticing that both the a/c fan and radiator cooling fan pull way too much amperage. Could it be the radiator fan module? I can't find any other posts with a failure mode where the fan drains too much power and cuts the car of at idle.

Or could it be the new aftermarket alternators? Maybe I need a 800 dollar one from the dealer??

Help please

Spike, please keep in mind that even though the alternators for our cars are rated at 160 amps, they do not put out 160 amps at idle. They only put out about 90ish amps. I would try doing the same tests where the voltage goes away but with the engine RPM up at 2000 RPM or so. At that point, the alternator should be able to output the rated 160 amps. It may be simply that you are running too many things while at idle and the alternator is getting overloaded.

The other possibility is that the wire between the ECU and the alternator is near something hot and once the motor gets up to temp, this is putting a high resistance into the wire, leading to the voltage going to the field of the alternator to dip, which will then drop the output of the alternator, leading to what you are seeing. This can be confirmed by doing a voltage reading of the field wire at the alternator. If you see that voltage not at 12 VDC when the alternator cuts out, then you are loosing the voltage in the wiring somewhere.

Spike,Chris has a good point, also If you have a weak battery that a strong alternator is masking but then at idle it falls down when there is a extra load. A good fully charged battery has a reserve to handle sudden power draws and is used as a buffer for such instants but if the battery is marginal the alternator has to work extra hard to keep the battery charged and supply the extra draw and at idle it can't because of the lower Amp. output. You can do a preliminary test by running at idle and put a volt meter on the battery, should rad 14.5 volts, then turn the car off and take a reading,hold tester on and watch to see how fast the voltage drops. A good battery will hold a charge a weak one will slowly drop or fast if is on it's way out. If it does have it tested free at a parts store to be sure.

Thanks for the replies guys,

The car did this with the old (less than a year) old battery and with a new one. The wiring from ECU to alternator has been tested to death and it does not seem to be the problem.

Chris;

You said u may be running too many things, but I do not have any aftermarket items on my car...,..Surely it can't be normal for a car to die after sitting for 15-20 minutes in idle with the a/c, front and rear fog lights on?? What do you think about the theory that the cooling fan is drawing so much more power than what it should that it's overwhelmed the alternator? I can not find anyone with a similar failure on their X type fan module

Thanks

Spike, keep in mind that the fan is rated to pull about 60 amps all by itself. Now you add in another 25 amps for the dash fan on fast speed, another 15 amps for the fog lights, 10 amps for just running the motor, you are suddenly up to 110 amps before you even start turning on headlights, wipers or anything else.

I do find your problem rather interesting as most people should have experienced this atleast at some point in there car. So, I do feel that there is still something going on. The question is what.

Just to make sure that we are not overlooking something simple. How are the battery cables? I could see where if they were questionable, it may be possible that this would cause an even higher draw on the alternator as the fan would be running slower, allowing more current to be pulled. This would be seen by the fans and the dash fan.

Thanks Chris everything in the charging circuit has been closely looked at : new battery, ALL the battery cables, positive and negative, are new, the alternator is new x2, and the ECU is new. The ECU to alternator wiring had been closely scrutinized, so at this point the problem is either something is drawing way way more than what it should or it's the aftermarket alternators I am using.

You mention the fan should draw 60 amps and this is precisely what the problem is. My mechanic says my fan that my fan is drawing close to 90 amps, and then when I turn the a/c, headlamps/tail-lamps and front and rear fog lights on, the alternator just can not handle it.....that's the question, do you think if indeed the fan is drawing over 60 the it's bound to be my problem??

Thanks

Spike
If your cooling fan is drawing 90 amps something should be getting hot eg. wires to the fan, the fan motor, relay.

Spike, if your fans are pulling 90 amps, they need to be replaced. That is way too much and that is probably the main source of your problem. I would start there and then see what you have.