Various Idiot Lights and Intermittent Symptoms

kevanski wrote:

When you're an old geezer, stuck in a small town, just moved there and don't know anyone, don't have automotive electrical skills, there's no space to work on your car, the mosquitos are as thick as soup, you're miles from the nearest city and you don't have a second vehicle, you will have no choice either!

I understand. It's just amazing what they charge. Too bad you didn't live near one of us. I help my neighbors all the time.

I'll send you a map and you can move in. You can join all of us under the old stone bridge. bring warm clothes!!!

Labour was only $70, but they hose us for parts etc. in Canada.

Well, not too bad considering you only paid one hour's labor. That's about right for installing those items. The "heat sink" you're referring to is probably the thermistor near the battery, a sensor which tells the alternator how much voltage to put out based on measured temperature at the battery. The idea is that batteries like to be charged with higher voltage when cold, lower voltage when hot. The thermistor shows resistance when it's cold, telling the alternator to increase charging voltage. When the battery is fully charged, it gets warm, so the thermistor tells the alternator to cut back. Bypassing to straight 12v just tells the alternator to put out the same 13-14 volts at all times. This is probably safe for a while, but not optimum for getting the most life from the battery, and could be the reason your battery failed sooner than later. When yours got hot, the alternator didn't know, so it kept throwing full output until the battery finally died. The weak battery created additional demand from the alternator, causing a domino effect.

The thermistor should not be that expensive. I just bought a good one for $20 online. Considering its job is semi-important, I'd look into getting it replaced if you can.

I agree with Aaron - I'm sure he meant "thermistor"...

Now, I don't think this thing is very important on a car with a "back-seat" battery. Our batteries don't face the temperature extremes that conventionally-mounted ones do. Furthermore, I bought the only genuine Delco replacement for our batteries 2 years ago, and the case of the new unit doesn't even make contact with the thermistor-compartment in the positive battery terminal...
[Speaking of which, have your battery cables/terminals been replaced, eliminating the spot for the thermistor?]

However, if some idiot actually cut out the thermistor and left the wires either open or shorted, there is no telling what the results could be. I've been looking at the charging section of one of my manuals and I officially have a headache... I earned one electronics degree, but A) I didn't realize that they decided to digitize the frickin' alternator controls; and B) they must not expect regular mechanics to understand this thing either, cuz not all the wires in the schematic are complete.

Given this, if I were you I'd get my meter out and start checking the cold/post-start charging voltage and the warm/full-battery charging voltage. If things are out of range, I'd get a thermistor and reconnect it and just tape it to the back of the battery.

If my back weren't extremely FUBAR right now, I'd pull out my back seat to check. Perhaps someone else can confirm, but I suspect this is the same unit as our cars have:
http://cgi.ebay.com/ebaymotors/1995-AURORA-GM-BATTERY-TEMPERATURE-SENSOR-THERMISTOR-95-/270754338001

The positive cable assembly with thermistor, new, is over $100 from RockAuto.com. There are two:

ACDELCO Part # SOSX1342 {#12157068}
[Flag indicates this part fits vehicles manufactured for the US Market.]
[Flag indicates this part fits vehicles manufactured for the Canadian Market.]
CABLE,BAT POS 3403.6MM LG (Only 1 Remaining)
$153.79

ACDELCO Part # SD137XT {#88864208}
[Flag indicates this part fits vehicles manufactured for the US Market.]
[Flag indicates this part fits vehicles manufactured for the Canadian Market.]
CABLE,BAT POS 2 DOORS
$100.79

The GM # 12157068 cable was also used in '91 Le Sabre and Olds 88 models. Maybe one can be got form a junkyard. Also, knowing GM, most of the similar BOP (Buick Olds Pontiac) cars that size '91 - '99 may well have a similar charging system and someone with some electrical savvy should have no problem splicing in a working cable. Might want to ask at a used car lot to refer you to who they take cars to for electrical work, and then get that shop to fix the thing properly.

By the way that delco alternator was under $160 including core from rockauto.com -- I wonder if the mechanic you used was seeing a very high price for the cable, like $300, and thought you would object (or faint).

You might want to get the cable yourself then have it installed, talk to whatever mechanic you're going to use first about that.

Good luck

Albertj

Hi folks, here's an update.

Picked up the car from the body shop today. The bodywork looks good. Started the car, the "air bag" idiot light came on and stayed on. The driver seat adjustments didn't work. Put the transmission in drive but... it pulled away in third gear.

(long string of foul language deleted here)

It was late in the day so I drove it to the mechanic, told him what had happened, and left it there. I'll touch base with him tomorrow.

Here's the history again, because I think there's a clue in here somewhere:

Everything had been getting progressively worse and worse over a period of three months, more and more idiot lights coming on, more and more things not working, up until Friday June 17. That was the first time the cooling fans quit working.

Then suddenly, Friday evening everything decided to work perfectly again, which it hadn't done for three months. The battery warning light on the dash was the only idiot light on, but I ignored that because I'd learned not to pay any attention to the idiot lights coming on intermittently! Cooling fans, cruise control etc. all worked perfectly. But the battery was draining and dead after a couple of hours of driving. About five minutes before the battery was totally dead, everything started malfunctioning again, this time including the speedo and tach.

I just made it back home, put the battery on a trickle charger for 24 hours, but it didn't hold the charge. That's when I had a new battery and a new alternator installed. The mechanic said the alternator was only putting out 7v and the battery wouldn't hold a charge on his big charger.

Here's where I think there might be a clue as to what's wrong. On Friday evening, for some reason, either the alternator quit charging, or something prevented the charge reaching the battery, or something falsely told the alternator the battery was already charged, or the battery itself didn't want to accept the charge, or something else I haven't thought of. But... under those conditions, everything worked perfectly! Even the battery warning light worked perfectly! Ha ha!

So what does that mean, if anything?

Kevanski

bad computer?

Get a volt meter and measure voltage at the (+) terminal. It should be ~12v with car off, 13-14v running. If anything different, the new alternator and/or battery are not doing their jobs, or something wasn't installed right.

Has the SES lamp come back on?

Please tell me when (if ever) do you plan to replace the factory-type battery cable?

Hi,

Just had a quick read through thid thread, one thing came to mind... the vent tube is there for a very good reason... to vent off explosive gasses hydrogen and oxygen. All batterys mounted in side the car cabin need to be vented directly to the outside!.

May be i missed some thing? what year is your car? i have a spare computer i could send you if its for a 1995. it has an intermittant fault on it but is good for testing. the fault on it is turns the ignition off once in a while. PM me with your address and i will send it to you if your interested.

i just replaced my battery and alternator for a similar reason (minus the idiot lights) Two cells dead in the battery (measured 8.4V) and auto zone tester commented low CCA and battery needs to be charged.

Just my tuppence worth.

Nigel Fenton

Here's a question for kevanski. Did you ever get the car scanned to find the code responsible for the SES lamp? I know you said the mechanic told you voltage was low, but it would be interesting to know what the car had to say about it. Those codes are probably still in memory unless your guy deleted them.

The reason I bring that up: if the alternator was putting out only 7v when you took it in, it doesn't mean that was always the problem, or the only problem - it only means that's what was happening on that day. If there were a high voltage situation for an extended time prior to that, the alternator may have given out eventually (components have a tendency to fail in such a situation). What's saying other components weren't permanently damaged as well? It's speculation on my part, but it would explain how things are mysteriously acting strange after 'fixing' the problem. Only reading the codes will tell...

Sounds like a PCM, that or a ground issue. Did you check the grounds for everything especially the PCM/BCM?

OK, here we go. Problem solved - almost! Kudos to "Bob"! The local Buick dealer told me he was their best man for these kinds of problems. Here's what Bob told me, but bear in mind this is third hand and I'm not an expert, so I'll tell the story as best I can...

Bob checked out the CPM and it was fine. He noticed right away the battery thermistor was missing and the wires fused together. He explained most Buick, Olds and Cadillac cars in 1998 and 1999 installed the thermistor as an experiment that never worked well. The idea was that cars with a heavy accessory load on the battery could be charged at 17v, and if the battery got too hot, the thermistor would cut the charge back to the normal 13.5v.

When the previous owner (?) removed the (probably failed) thermistor and fused the wires, the battery always received a 17v charge. That would boil the battery and eventually fry it. He thought that may also have fried the alternator, but he wasn't sure about that.

He said the CPM was designed to operate between 8v and 16v, so I guess the CPM didn't appreciate that constant 17v, and it "acted up". That resulted in all the idiot lights working like a xmas tree, loss of cruise control, loss of cooling fans, loss of all but third gear (limp mode) etc. etc.

The permanent fix? Replace the thermistor. GM doesn't make them any more, so I have to find one off a scrap (shed a tear!) Riviera. He wasn't sure if 98 and 99 Cadillac and Olds would work.

The temporary fix? Simple! He removed the 10amp fuse marked "BATT THERM" from the box next to the battery! And everything worked normally! Yee ha! Well, almost...

He explained the battery charge light on the dash will remain permanently on and cruise control (CC) will not work. He explained why specifically the CC would not work, but I didn't understand the explanation. The CD player doesn't work either, but I forgot to ask him about that.

Anyway, I can live with the exceptions until I can find a working thermistor.

Thanks to everyone for their ideas and input. I hope my experience will save someone else a lot of hassle and expense trying to diagnose the problem.

Cheers!

Kevanski

Aaaaaaah!

I forgot to mention, yes, I previously cleaned all the grounds - thanks Dave and Albertj! Also, I wrote down the codes on a very small scrap of paper that I had handy at the time, and you can guess the rest... :-)

Going back and reading all the postings. I think you had it nailed with your first posting, Aaron - "Your symptoms seem to suggest a high voltage situation. If over 15 volts while running, the alternator needs replacing/rebuilding. I think the high voltage could also damage the battery, causing the bulging you mention." If anyone else has this problem, tell them to pull the 10amp "BATT THERM" fuse and see what happens.

I wished I had had the resources to follow up on your diagnosis, Aaron. It appears you have considerable knowledge and expertise!

Albertj, I'll follow up on the ACDELCO P/Ns you mentioned. I'll check out RockAuto.com shipping across the border. Unfortunately, anything not wrapped up like a birthday present from your 90-year-old Grandma in Nebraska and mailed USPS usually gets targeted for taxes, customs duties, brokerage fees, additional shipping costs, etc. when it crosses the border into Canada... NEVER ship to Canada by UPS. They are by far the worst for nailing you with extra charges.

Mark, you mentioned about digitising the alternator. I think the mechanic said something about the original alternator communicated with the CPM, and he expressed concerns about contemporary alternators not communicating properly with the CPM.

Thanks to anyone else I failed to mention. Every little bit of help is appreciated.

Kevanski

Kevanski, thanks for the followup. A big part of what makes our forums work is when members visit back and post results. That's how we learn what's right and wrong around here - reporting real world experience confirms our opinions.

I'm glad you know more about the situation now, but one part doesn't make much sense to me: the temp fix for the thermistor. To my knowledge, when the thermistor circuit is broken or disconnected, that's when a high voltage situation would occur, NOT when the thermistor itself is bridged (shorted). When you short the thermistor, the result should be a full ~12v current from the battery to the alternator through the sensor lead. This should command the alternator to run normally, in the 13-14v charge output range. By pulling the fuse, I would suspect this might compromise things, but I've never tried it. I'm sorry, but I have no idea how that thermistor can effect the function of the cruise control, and if my battery lamp were on all the time, I would not be all right with it. If it were my car, I'd short the thermistor lead to 12v until I could replace with the correct part. Not saying your guy is incompetent, but this does not seem correct. That battery lamp is telling you there is a problem!

But again, the really important thing is how much voltage is actually charging the system. This is the simplest, surest way to know if things are working properly. It's as easy as using a voltmeter to read the voltage with car running & off. I would be leery of running with any temporary fix until I saw with my own eyes that charging voltage was in the correct range.

As I understand it, the thermistor just 'rigs' the input to the voltage regulator. Without a thermistor, the voltage regulator should act normally, supplying it's target 13-14 V.

That's interesting. The "voltage booster" mod uses a diode in-line with thermistor to attenuate the sensor wire voltage by -.6 volts. This corresponds to an increase in charging voltage of about the same amount (~15v). Using two diodes in series on the thermistor sensor wire would result in a +1.2v increase (~15.6v) in charging output. As the sensor voltage goes lower, charging voltage goes higher, and vice versa. Maybe that's not the case when sensor voltage goes to zero?

My answer is not correct.

Here is also not the answer I was trying to find, but I found a nice article taking you start to finish through alternator diagnosis:

http://www.motor.com/magazine/pdfs/092007_10.pdf

Quote :

Remote-Mounted Batteries
You may have to diagnose a no-charge condition on a GM car with a remote- mounted battery. The alternator isolation technique in such a case is exactly the same as the one I just described, but it may require an extra step. Here’s the info you need.
GM’s G-body cars of the 1990s, which include the Buick Riviera, Olds Aurora and Cadillac Allanté, have a battery mounted under the rear seat. The charging system on these cars also may have a thermistor that monitors battery temperature. If so, the thermistor is located at the positive battery terminal and is wired in series between the battery and the alternator’s S terminal. Note that on the alternators discussed in this article, the S terminal is always at the opposite end of the harness connector from the P terminal.
First, check the wiring schematic for the particular car, or else visually inspect the positive battery terminal area. If the car is equipped with a thermistor, you must recreate the thermistor-style sense circuit in order to test the alternator accurately. Go to the electronics store and get a resistor or combination of resistors totaling approximately 1800 ohms (1⁄2- watt resistors are adequate for this task).
Make a jumper wire that’s long enough to go from the alternator’s S terminal all the way back to the positive battery terminal. Carefully splice the 1800 ohms of resistance into this jumper wire. Now, the alternator should operate normally with a low-current bulb in series to terminal L and an 1800-ohm resistor in series to terminal S.