Need some help!

Last week I dropped off my '04 S-Type to my local repair shop complaining that there was a slight mechanical odor at times. The shop diagnosed the odor being that of the alternator...and that it was shot. On Monday a new alternator was delivered and installed but since Monday the mechanic cannot figure out why the Check Engine light will not turn off. They have now been trying to get the light switched off for a 24 hours. From what I understand, they think maybe the new alternator created an "excessive ripple," thus possibly destroying the engines CPU. They are not 100% sure yet but they want to do a temperature test at 65 degrees and then when it is crazy hot outside.

Okay, I admit once again, I do not know a lot about the mechanics of a car but am learning. Nonetheless a couple questions:
1) Does the above make sense and could this happen?
2) Any idea on what a new CPU/ECU whatever it's called would cost?

Thank you SO much in advance! Cheers!

 

I think they don't know what they are doing??

Is this a shop that works on Jaguars or just an auto repair shop?

While an Alternator can fail and put out excessive voltage if it's enough to fry the PCM you should have just about everything else in the car fried too!

Get some numbers. What is the output voltage of the new alternator?
What was the output voltage of the old alternator?

Please get the codes read. Turning off the light is NOT the problem. The problem is what caused the light to turn on?

This is pretty basic stuff so I hope you have just miss-understood what he is saying otherwise I think you are paying a mechanic to train on your car!

If the PCM is destroyed does the car run?
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Thanks Tbird6. I jut got off the phone with the shop and have answers to your questions. To begin with this shop is not Jaguar/Import Shop but does have 28 years of service and is recommended in the area.

Here we go... !!!

- Output of new alternator 14.08
- Output of ol alternator 8.0
- No Codes are being read.
- MY ERROR: Engine light is not on, its the Battery Light on.
- Car is Running
- Before the new alternator was installed the following was checked: Charging system, battery fuse, ground circuit - all were ok.
- Alternator is charging...(I guess battery?)

To trouble shoot, they took the new alternator off the car and replaced the old and it read 8.0 again.

The said they will also try a Press Test on he ECM, maybe some corrosion on some of the pins?

Hopefully that hlps!

 

OK that sounds a whole lot better!

I think 14.08 is a bit low for the output but certainly within range. I am used to seeing 14.5 or even a bit higher. But like I said you are within range and should be fine at 14.08.

The battery light does not have anything to do with the PCM so I am confused on why they are looking at that?

Be aware it's not unknown to get a bad alternator right out of the box. Our cars like most modern stuff has the voltage regulator built into the alternator itself. So the regulator could be bad while the alternator itself is OK.

Any chance they can try another known good new or used alternator? I think it's too much of a coincidence that the new alternator was installed and you still have the battery light. I would focus on that.

Did you have the battery light on with old alternator? You should have if it was only putting out 8 volts.
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Tbird6,
My battery light has never been on for any length of time. There was one point that my car would not start, after I parked it and ran into a building to see a customer. Came out it would not start. I waited a bit and the engine restarted. I then took my car directly to the nearest place I could think of, SEARS and they placed a new battery in the car.

Not sure on an alternate alternator test but will check with the shop.

I have never had any issues before this week!
Scott

 

"excessive ripple" implies an AC component is being read at the output terminal of the alternator.

combine that with the battery drain and a defective diode trio or regulator is indicated

that would mean the replacement alternator was defective out of the box.

 

Sounds either wrong kind or faulty or both.

There's signalling between PCM (aka ECM) and the alternator so they must fit the right kind. 14.08 sounds rather low. Proper figures are in JTIS.

 

Thank you all for your help! Glad you all are out there to assist! I will let you know what we find out!
Scott

 

+1

Excessive ripple is typically due to a faulty regulator in the alternator. Sounds like the new one they put in was probably some Autolite junk or something from Advance Auto Parts or whatever cheap parts warehouse and was probably poorly remanufactured and no good.

I would take the car elsewhere. There are far too many fuses between the alternator and ECU for it to damage anything computer related.

 

I don't think installing an alternator that was broken out of the box is necessarily sufficient reason to dump a shop. These things happen.

Excessive ripple is more likely the diode trio than the regulator ... in my mind.

 

I agree! Thank you all for your posts, I have forwarded to the shop and they have heeded your advice and are going to attempt a different new alternator and see how it goes! Day 7 of being in shop, but my gut says that I will have my baby home today!

 

I'm not saying dump the shop over the alternator; but if they think the alternator fried the ECU and have had the car for 7 days then it might be time to think about having a different place check it out.

 

i AGREE^^^^^^. No matter how nice they are, if they can't get to the bottom of something this basic and in addition believed that the new alternator may have damaged the main ECU (even though the voltage is actually on the low side)they really don't know what they are doing, sorry.

Dave

 

Case closed hopefully... Good news the new replacement alternator arrived yesterday and it did the trick. No issues...

Then...this AM drove the car to work and my dash board looked like it was Christmas in May! Every red and yellow light seemed to come on. I was getting ABS Fault, Transmission Fault, Engine Light was on, Battery Fault, safe mode, etc....

I drove the Jag over to the repair shop and guess what? No lights, no warnings, nothing. Not even a gift from Santa.

Bah hum-bug.

 

Maybe flattish battery that recharged just enough as you drove over. You'll soon know if it's dying

 

Exactly what I was thinking!

 

Hi Scott,

I've been following this thread with interest. I ran into the same exact Christmas tree phenomenon on a '96 Lincoln Continental. I believe our Jags use the same FoMoCo engineering for the electrical supply system. The alternator failed without any way to know, as there was no voltmeter. Once the battery voltage dropped below a certain level, ALL kinds of craziness started happening, much like you've described. Curiously, it wasn't until the voltage dropped even lower that I got a "check battery voltage" message, but that was several minutes after everything else started going haywire. (I had about 10 minutes to home via back roads and neighborhood streets, and since the car was still running fine, I kept going.)

After a little research, I found the battery light does not function like the old "idiot" light of old. Most of us are probably used to the version that turns on when the battery voltage is higher than the charging output, e.g. a failed alternator. It was even normal for the light to come on dimly at idle with high electric loads. On the late model FoMoCo version, and I'm pretty sure Jag uses the same logic, the battery light is simply an on/off output controlled by the alternator to show an internal problem. In other words, light on = alternator not valid. The rub is that the alternator still has to be at least partially alive to control the light. If the alternator goes completely dead (such as in my situation), you never get the warning light. You did mention getting the battery light so this doesn't appear to be your case, but keep this in mind for any future failures. A lack of the battery light does not conclusively mean the alternator is good.

You have had two alternators, so now it's time to do some serious head-scratching. My hunch is crimp connection on the big output lead at the alternator. Late model Fords are notorious for this. It's such a common problem, aftermarket repair kits are even available. Don't just do a visual inspection and call it good. Run a voltage drop test across the suspect connection, as I've detailed at the following link. Better yet, run the test between the alternator's output terminal and the battery (+) terminal, and then between the alternator case and the battery (-) terminal. You'll need a long jumper due to the battery location, but you could easily rig up something from scrap wire. This test only takes a minute or two and will rule out all sorts of problems. I am an avionics technician and use this test frequently and will swear by it for finding marginal connections:

Voltage Drop Testing


Keep us posted.

 

There is a voltmeter - can be seen via OBD or ETM.

 

Just to make sure...

I have a suspicion that my new battery has been drained due to the alternator, maybe causing all the dash lights to be on. So this morning I took the Jag out and ran it 40 miles at 1,500 RPM or higher. I wanted to see if this would recharge the battery as I drive less than 8 miles to work each day. After the run. The only light on is the check engine light. I am going to monitor over the holiday weekend.

 

Has the check engine light been on before? Or was it on along with all the other lights?
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