When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
The battery icon lit up on the dash as my wife was driving her 2006 XK8 a couple of days ago. She was about 30 miles away but managed to get home safely with no issues other than the battery icon staying on. The car stayed parked until yesterday afternoon when I moved it about 100 feet - the battery icon on the dash again lit up and stayed on....
I installed the current battery (a Bosch 49/850B Vented) in April 2017. I installed the previous battery (also a Bosch 49/850B Vented) in September 2012. In neither of those cases did the battery icon on the dash ever light up prior to needing a replacement battery. So this time I suspect the alternator but I have a CTEK charger attached to the battery today in an effort to find out if it indeed will take and hold a charge....
To my knowledge the car still has its May 2005 build-date factory alternator (I assume it is a Denso unit but have not yet checked). I have read here on the forum that these cars do not like replacement alternators and will often illuminate the battery icon on the dash full-time if a replacement alternator is installed, even if the new alternator is working properly. So if this factory alternator is indeed failing or has already failed, I plan to have it refurbished by a relatively local shop specializing in alternators and starters....
To those of you who have removed your alternator for refurbishment/replacement on these 4.2 engines, any tips, tricks, and tool recommendations would be much appreciated. I have reviewed the recommended removal process on my JTIS CD and while it is helpful, there is nothing quite like the voice of experience from those who have already been down this path....
If my issue indeed turns out to be a faulty alternator, I do not look forward to doing this job in our July heat and humidity....
Hi Jon,
NB this is for the 4.0, but I don't think there's much difference?
Some advocate removing the fans & shroud to give enough wriggle room to remove the alternator from the top, but I found that this wasn't necessary once the air box was removed.
(I did have to remove the ignition suppressor and its bracket, but fortunately you won't have that to contend with).
There is a collar that is a press fit into the rear lower mounting that is meant to slide to take up any slack when the bolt is nipped up (you can just see this in the pic.). This can make breaking the alternator free difficult as it may stick tight over the years, so it needs to be moved back into the mounting.
You can do this with a long threaded bolt, a nut and a collection of washers once the bolt (2) is out: I found there was just enough space to get a ball joint breaker in there. Still needed a bit of persuasion with a BFH, mind.
Getting to the connections on the back - particularly the large cable (7) - can be a challenge.
Probably took me the best part of 4 hours, but I don't move at any speed and the suppressor bracket was a pain to R&R.
edit: I think the problem people have experienced with replacements is that either some of them don't have the third wire or the regulator is different. I used a Denso rebuild with no issues
Last edited by michaelh; 07-03-2018 at 01:43 PM.
Reason: afterthought
Jon, if there's a question, just hook up your volt meter to the battery, car running ac on. Headlights on. Still gettin g 13,5 or more volts? If not shows alternator is bad. If easier just ask local auto parts place to test.
yes I've seen battery light with bad alternator.
john
Did your factory alternator drop dead all at once, or did it gradually fade away? And when it failed, did your battery icon on the dash illuminate?
Hi Jon.
Yes, it was sudden death, but I got pulsing lights, pulsing engine speed, voltmeter up to 17V, and most of the dash error messages that the car knows when I started her that morning.
Turned out to be the regulator (and this may well be your issue), although I replaced as a unit as I didn't want to do the job twice.
If you follow Johnken's suggestion and the output voltage is holding up under load at least you might be able to defer until the heat/humidity drops. Weather is the same here atm which is all well and good until you actually have to do something.
If my issue is indeed the alternator, I found a relatively local shop yesterday that will refurbish it for $125 to $150 assuming parts are still available. If it is indeed a Denso unit, getting the parts should not be a problem....
Looks like the alternator has indeed failed. With the engine running at load with headlamps and A/C on, my multimeter never registers above 12.2 volts at the battery terminals. And the battery icon remains illuminated on the dash....
Any additional tips and tricks regarding pulling and then reinstalling the alternator on this 4.2 engine would be greatly appreciated....
Just to be sure, have you checked the voltage closer to the alternator? Fuse blocks, diagnostic connector, or even on the alternator itself? There were reports of bad battery cables, so I assume they would offer resistance and voltage drop under high load. Check the temperature of these cables, too. A bad ground would also show voltage drop. That being said, I am not sure where that battery icon takes its reading from. Other sources of high load would be the heated seats (if they even kick on in summer) and the rear window defroster.
I have not checked the voltage anywhere except at the battery. Judging by what I have reported thus far, several folks with automotive electrical experience have advised me that the voltages I have reported along with the battery icon lit up on the dash point squarely to the alternator....
Can you elaborate on the reports of bad battery cables? And is there a 100% foolproof test that proves the alternator is indeed the faulty component?
Can you elaborate on the reports of bad battery cables?
I have not had to replace mine, but the (short) cables between the battery and the block in the trunk have reportedly failed internally for some folks, and cause voltage drops, etc. Such cables are hot to the touch, but show no visible signs of problems (the terminals are fine).
For your situation, I would say check the voltage at the alternator itself. For example, if there is a problem with a ground strap or a hot cable, the alternator could be generating 14V just fine, but because of the high resistance, the rest of the car could only see the 12V you have at the battery. As replacing the alternator is quite a bit of work, checking the voltage first seems like time well spent.
I had planned to remove the airbox / air duct / MAF sensor to gain better access to the alternator. I don't want to crank the engine with the airbox / air duct / MAF sensor removed because I know it will throw codes and cause all sorts of problems. Don't really want to crawl underneath the running engine to get to the alternator terminals that way, either. So how do I safely (for me as well as for the car) check the voltage at the alternator terminals when the engine is running?
Negative would be the engine block, anywhere, positive is that fat cable (7) in the picture above. I have not done this myself, so I have no specifics.
Alternative would be to locate a positive terminal at one of the fuse block and measure the positive there. Also, measure the voltage difference (if any) between the engine block and a negative fuse block terminal.
This morning I decided to use my my iCarsoft i930 scanner to determine if the car has thrown any codes pertaining to my ongoing battery vs. alternator issue. I have not checked for any codes in at least a couple of months so there is no telling how old the codes that showed up today may be. I manually scrolled through the various modules that the i930 can typically read. Here are the codes it picked up:
Using my JTIS CD for OBDII DTC code interpretation, I see that these codes come from all over the map. They point to the ignition switch, the airbag circuit, the headlamps, the transmission, the door modules, the seat modules, the security system, and the Dynamic Stability Control system. Several of them have multiple interpretations. Several of them do not show up on my JTIS OBDII DTC chart at all. Some if not all of these codes are certainly spurious (perhaps triggered by alternator failure if it has indeed failed). But how in the world do you tell?
What is interesting (and frustrating) is that some of these codes can indicate open circuits or short circuits in the various modules or systems that they are associated with. That could lend some credence to the hypothesis of a working alternator but a potential electrical problem somewhere else....
Keep in mind that the battery icon on the dash remains illuminated whenever the engine is started, so most folks who have an electrical background far better than mine seem to believe that the alternator is indeed faulty. The big question that I keep pondering is whether or not a difficult-to-find electrical fault somewhere other than in the alternator could cause that battery icon on the dash to turn on and stay on. Does anyone know the answer?
Wayne (cjd777) schooled me this afternoon on three different locations on this XK8 to measure the DC voltage. One is in the trunk, and two are in the engine bay. When our blistering temps cool off here tomorrow, I will use my new multimeter to take those measurements. Like you, he also suspects a faulty alternator. More specifically, he suspects a faulty regulator inside the alternator....
07-03-2018, 12:49 PM
Battery vs. Alternator....
