My alternator was putting out to much voltage. I had it changed. Now my battery light is going off and on, or doesn't come on, or stays on while driving. Is this my computer?? I say that because they tested it and the batt and both were good! How to I rectify the situation and what's the money looking like?

 

First of all check all the ground points for proper connections

 

Hi there was going to give same advise. Check batt to body and engine earth .as the same thing happened on my x type fitted new batt same prob fitted new alternator same prob then found the the engine earth strap here had come very loose.removed cleaned copper grease refit same with body strap problem solved. Stupid oversight on mine not checking 1st and cost me £160.00 batt alternator)
Hope helps

 

Lotion, I would say to first start with whether you have a true undervoltage condition or not. Connect the multimeter across the battery and that will tell you. After that, checking the wiring going to the battery would be a good second check. After that, it may be possible that the plug on the side of the alternator has got some water in it and that is creating havoc and/or the plug is not on all the way and it is making intermittent contact.

I guess the other thing that I would have to ask is what amperage alternator did you get? If you only got a 120 amp unit, it may be that you are simply overloading the alternator and that is what is dropping the voltage down. If you can turn all electrical stuff off (except the essentials) and the battery light remains on, then you can rule this out and you need to be looking at a wiring issue.

Granted, just because it is a "new" alternator, does not mean that it doesn't have an issue. I have seen more than my fair share of problems with new items getting installed and failing shortly there after.

 

What is the engine earth? Im about to go outside now and start checking anything around the batt.

 

What number is "too much voltage"? The ECU controls the alternator voltage and uses a two stage charging program. Did you put in a real Jag alternator or some e-bay junk?

 

Thermo, I hot a 100 amp alt and your right on bc I turned off the electrical components I.e. lights, ac etc and it goes off. The multimeter is reading good as far as the batt and alt is concerned.

 

Lotion, engine earth can be also called engine ground, or more simply any metal part of the engine. The whole engine is grounded to the body of the vehicle. If you look, there should be a large gauge wire running from a bolt on the engine to the body of the car. This is what makes the engine "engine earth". All the power that your alternator makes returns via this wire and runs through the engine block back to the case of the alternator. So, your problem could be something as simple as you have rusty surfaces between the alternator and the engine block. But, normally, this is not an issue as there is enough surface there that even if one area is corroded, there are other places that it is still making contact.

 

Tony_H, I got the alernator from any auto parts store. Can it still be bad even if it reads good through tests?

 

Thermo, I didnt look at that yet. I just checked the battery cables and it "looks" just fine. I will check the earth ground cable. THIS DIALOG IS GREATLY APPRECIATED EVERYONE ♥

 

OK, this is from the service manual

The engine control module (ECM) can switch the voltage regulator between two voltages to optimize the charging of the battery.
The low voltage regulator setting is 13.6 volts and the high voltage regulator setting is 15.3 volts, measured with the generator at 25°C
(77°F) and charging at a rate of 5 amps. These values decrease with a rise in temperature or current flow.
The ECM determines the voltage setting of the voltage regulator. The high voltage setting is always selected by the ECM once the vehicle
has started. The ECM determines the period of time that the high voltage setting is selected for.
There are three different time periods selected by the ECM which is dependent upon the vehicle conditions when the vehicle is started:
The longest time period is selected if the ECM determines that the vehicle has been 'soaking' for sufficient time to allow the engine
coolant temperature (ECT) and the intake air temperature (IAT) to fall within 3°C (37°F) of each other.
The intermediate time period is selected when the ECT and the IAT is below 5°C (41°F).
The shortest time period is the default time and is used to provide a short period of boost charge.

A fault in the wiring or the connections from the generator to the ECM, will cause a fault code to be generated and stored in the ECM and
the charge warning indicator lamp to be displayed in the instrument cluster (IC) after a short time.
The charge warning indicator lamp is operated by the IC after receiving a signal from the ECM through the control area network (CAN).
With the ignition switch in the RUN position the charge warning indicator lamp will be displayed in the IC when the generator is not
generating power.
If a fault is detected with the generator a fault code will be generated and stored by the ECM. The charge warning indicator lamp will also
be displayed in the IC.

 

OK!


Thermo: I checked the battery cables and they look great. As far as the engine earth, I know the general location but I couldn't get to it to check but its on the opposite side of where the auto shop was working and I didn't have this issue before the alt change. Never seen the batt light come on prior....


Tony_H: So your saying that I need to check the wires that go from the ECM right? I will have the auto shop do that because I cant reach it.


I just took it to get the alternator checked again and their system said that it was good but there was a leakage. It didn't say where of course. The light now only flashes intermittently even with all the electrical components off i.e. lights, radio, a/c.

 

Lotion, the easy check that I would do is to simply put the red lead of a multimeter on the body of the car and the black lead on the engine block. You should in theory see 0.0 VDC. But, in reality, you are going to see a little something. Anything less than 0.5 VDC is considered good. You want it as close to 0.0 as possible.

From what you are describing, if the cables are good (you can do the same checks, just going from one end of the cable to the other, preferably going from say the post that the cable bolts to to the lead post of the battery), then you are most likely looking at a either a loose plug on the alternator or the wiring at the plug being bad.

I think the big thing that you also need to do is to take the multimeter and connect it up to the orange/green wire going to/from the ECU and alternator. If you are getting the low voltage light and this wire is up at around 12 VDC, then this almost confirms a bad alternator or connection inside the plug (the last option being the power wire from the fuse box that powers the alternator). If you are getting the light and this voltage is not up at 12 VDC, then you are looking at an ECU issue (assuming you get the same voltage at both end of the orange/green wire, if you get a voltage difference, then your problem is the orange/green wire).

It may be worthwhile to simply replace fuse F6 in the engine bay fuse box (only applies to the later 04+ year cars, the earlier cars, you should be getting issues with the transmission too if you are having problems with this fuse). If that fuse is dropping voltage, it can be causing the alternator to not get sufficient power to create the field in the alternator. If you can get a multimeter on the alternator, you should be seeing battery voltage there on the green/red wire.

We will get you taken care of.

 

Thermo, before I perform all that you have instructed, all these readings have been performed when the light is NOT on. It doesn't stay on long enough. To me that says that the alternator can still be bad since it has only been read when the light is off. Make sense???

 

I cant reach the wires on the alternator so should I have the shop do it? I see a lot of orange/green wires on the ecu, which block is it coming out of?

 

Lotion, the orange/green wire at the ECU will be in slot 65 (if you look at the plug for the ECU, it will be near the center, in the center row, left of center, 3rd from the center).

I would say that if you can atleast see the wiring for the alternator, see if any of the wires related to the alternator make a sudden bend. This can indicate that the wire has broken internally and that is what is causing your problems. As the wire wiggles, the copper inside and make and break connection.

As for taking the car to a shop to work on, it may be advisable. Working on these intermittent issues can drive even the most knowledgeable crazy. I have to deal with problems like this at work and I have been known to loose a few hairs over it. It all depends on how much time you want to take and how bad you need the car to be on the road in a short period of time to the degree that you are fully confident with it.

 

Well I was driving late yesterday and heard the winding/swishing sound under the hood. Guess where it was coming from?! Yes! The alternator area. The sound sped up when I accelerated. O_o

 

HOPEFULLY THIS HELPS SOMEONE!!! I'm here at the shop and they said that the sound was the tensioner. I read this possibility while I was on the internet the ENTIRE day looking for people with the same issue I was going through with the battery light. As I was eliminating the options and testing and reading voltage, I decided to drive it at night when its quiet and really listen to the engine. That's when I heard the noise by the alternator and thought back to the person explaining about getting the tensioner right but some cars have auto adjust for it. They are working on the issue now. Fortunately the work is under warranty even though the part isn't. I will give an update when this is done.

 

......... *sigh* It was the alternator. For right now my light goes on and off not frequently but more times than none and I REALLY hope it doesn't do any damage to my car while its in there since I cant have it changed back til' next pay day because of how costly this was. Now I have to pay to have it changed again ugh! I will keep the driving to necessity trips only I guess. THANK YOU everyone for your concern, knowledge, possible solutions and outstanding output. Ive learned so much already.

 

Surely the replacement alternator you had fitted has a warranty.