My x-type has had the following symptoms. First, it had a battery light on. When I went to the local walmart to have the battery checked, I turned the car off and, thought, "what the heck, let's look at it again" so I turned the car back on and the battery light had disappeared.

Two weeks later, I was sitting in my car waiting on my son. I turned the car off. Then I turned on the electric but did not start the car. The engine fan ran for about 5 minutes or so. I got a DSC fault. I turned off the electric and tried it again. Another DSC fault showed. I got out of the car and got my son. When I turned the electric on and got a DSC fault, then, when I tried to start the engine the car had a hard time turning over - but it did eventually start. Then it said "Transmission Fault" and went into limp home mode saying "Cruise not available." It also had bad battery light.

I decided to pull it over after driving a couple of blocks with only very limited acceleration. I turned the car off. Waited 10 seconds then started it again. Everything was fine! No transmission fault, no DSC fault, no limp home mode, no amber light, no battery light. All seemed good.

I read here that a bad battery could cause a DSC fault because of insufficient voltage. I took the car to Walmart and they tested the battery (but would not check the charging system because of some stupid company policy - they used to do it). Battery was A-OK giving 689 CC Amps (rated for 700). I went to Autozone and they were kind enough to check the charging system. Their machine indicated that the voltage regulator failed.

Please correct me if I'm wrong, but I thought these cars don't have a separate voltage regulator - correct? My understanding is that the voltage regulator is built into the alternator.

My question is: Can a bad voltage regulator/alternator cause all those problems? (DSC fault, Transmission Fault, limp home mode, battery)??

Thanks for any insight.

 

it can
Buy a multi tester and check everything yourself.
I recommend this one.
http://www.harborfreight.com/clamp-o...ter-95683.html

 

alphacat, check the positive cable that runs under the battery box and up into the bottom of the fuse box on the drivers side engine compartment. Its possible that cable is arcing against the body bolt it runs across. Mine had the same symptoms as yours except it shut all functions down and then came back with the DSC fault, limp mode, etc.

 

alphacat, yes, a bad voltage regulator can cause what you are seeing. IF you know something about computers, they love a steady voltage. If you get a failing regulator (yes, it is built into the alternator), your system voltage can be jumping between 13.7 VDC and 12.0 VDC. While this doesn't seem big, it is enough to make the computer think all sorts of things are going haywire.

I would first start with something as simple as getting yourself a basic multimeter and connecting it across the battery. With the car off, the multimeter should be reading 12.6 VDC (if it is reading 12.7 VDC or higher, you have a low quality multimeter and its values are off by a little, if you are down around 12.5 VDC or lower, that battery needs to be put on a charger before going any further, if the multimeter still reads 12.5 VDC after having the battery on a charger, then you have a lower quality multimeter or a battery that is starting to go). While watching the multimeter, start the car. You should see the multimeter drop to around 11.0 to 11.5 VDC as the starter is turning the motor and as you release the key back to the run position, you should see the multimeter jump up to 13.7 to 14.4 VDC, hover there for a few seconds and then coast down to 13.7 VDC and be pretty much rock solid. If you are seeing fluctuations of more than 0.1 VDC, then your alternator is having issues or you are having battery cable issues. With our cars, the battery cables are more of a common occurrence than a bad alternator. Now, that isn't to say we have seen a few alternators die. But, unless you are moving the multimeter to the output post of the alternator and you are taking a guess as to what to replace now, the battery cables would be a good place to start (cheap and fairly easy to do, a new set of cables can be had at your local auto parts store).

 

I think 12.3V is normal for good car battery. Maybe 12.7 is for bike battery.

 

car5car, all lead acid batteries make 2.1 VDC per cell. It is a constant as the voltage is based on the materials used. The voltage only drops because the amount of acid left starts to drop and it starts putting some internal resistance into things and it is harder for the chemical reaction to occur, resulting in the lower voltage. All 12V batteries of a led acid design have 6 cells in them. If you start using other types of batteries, they will have a different voltage per cell (look at alkaline batteries, they tend to run at 1.6 VDC per cell as an example).

 

Some cars have voltage regulator in ECM. That was pretty stupid idea, if regulator goes bad, ECM has to be replaced. I am sure there is a way around it, I would install external regulator. Don't know about Jaguar.

 

You need one of those pivot mega raizin voltage stabilizers. Just don't get a fake one. They're supposed to balance out the battery volts to they are more steady and constant instead of fluxuating in pulses. I put one on my car and it did help some but I also used a set of thick grounding cables to ground various points of the engine to the battery's negative terminal. Made the car run smoother, quieter, and more responsive. Then again right now my car needs an engine so I shouldn't be offering tune up tips.

 

ca45car, Jaguar has a quazi ECM voltage regulator setup. The alternator actually generates the field for the alternator (inside the voltage regulator) to make the alternator output what it should. But, the ECM sends a signal to the voltage regulator to control at a voltage determined by the ECM. A lot of alternators are set up to control at just a single voltage. The Jaguar system can actually control over a larger range (about 2 volts) and they did this with the intention of giving a quick charge to the battery following the momentary drain from starting the car. So, what you will see is the car will start and the voltage is at 12.6 VDC, the motor will start and the voltage will jump up to above what it normally is so the battery will be forced to charge (this makes up for any energy that was lost during the starting process) and then once the ECM thinks the proper amount of energy has been given back, it will lower the voltage back down to its normal level. So, do you call this "voltage regulator in the ECM"? It can be argued both ways.

 

I don't know much about Jaguars. So please don't go far from this forum until I am done repairing mine. I used to repair alternators, diagnosing diodes, replacing brushes, but it was long time ago.
It seems like regulator is inside ECM.

 

car5car, the signal going from the ECU to the alternator is a very small current/voltage signal. The alternator takes this signal and makes it much bigger so it can generate the field. hence why I ask if you would call that having the regulator in the ECU. It is not 100% there, but parts of it are.