Alternator derived transmission issue . . . again

Hi Guys,

Sorry for the following long-winded request.

I have a 96 and am the second owner. A couple of years ago, it would start off in, third gear. Then the dashboard readout went whacky and the heater fans went on and off on their own. I was informed the tranny was shot and to drive it until it blew up.

Then the alternator died and everything else returned to normal. Tranny shifted, dash readout was correct, heater worked. Replaced the alternator and all the problems returned but eventually, driving for a half hour or so once the battery charge caught up, it worked fine.

That was a couple of years ago. I don't drive the car very often and it can sit for a week or more. My wife came to me to say it was "sluggish" again. Tranny problem returned. So, I drove it around a bit more and ran it in the driveway until I found the cooling fans didn't turn on. As before, shifting it manually works.

Disconnected the alternator and the car was fine.

I just put a new alternator in and the problems came back. Starts in third. Drove around for a while until I noticed that the fans hadn't come on again and it was starting to get hot. Checked all the fuses and wondering where to look now. Will test the new alternator in case I got a dud.

Any suggestions would be appreciated.

Adrian

Initial wild speculation - Sounds to me like you have a bad ground. There are grounds all over the car, you should check them all... main battery, engine ground strap, various wiring harness points, PCM (computer), etc all have important ground points.

Hi Derek,

Thank you for the quick reply. I'll see if cleaning them helps. Did all the battery connections when I replaced it last winter but will go back and check the ground there, too.

I burnt the ground on my van from the trans to the chassis and it wasn't shifting right. I thought it was the computer then the trans. I ended up replacing the ground strap with 4 gauge and 2 terminals and voila problem solved

Hi Ruben,

Thanks, I'll take a look tomorrow.

With the car off and the battery disconnected, what is the battery voltage. Measured with any common handheld voltmeter?

It's 14.1 disconnected, 13.7 connected. Battery is about a year old.

Tested the new alternator with voltmeter. From the Bat terminal to ground at idle it's putting out 19.7 volts.

I need some help describing this, but I think the problem may be in the thermistor circuit that helps regulate alternator output.

Hi guys,

Thanks again for your advice. Still having the same issue. Put in a rebuilt alternator and the issue persisted. Realized that I should probably avoid the Chinese alternator, returned it and put in a rebuilt AC Delco. Slightly better for a few days. Alternator output was still on the high side according to the specs (18-19v at the bat terminal on the alternator). Returned the alternator (wonder how long Amazon will keep accepting electric parts for return) for another ACDelco.

Drove the car and it was fine for a few days. Drove it again and for 15 miles the problem returned. Once I arrived at my destination, stepping on the gas would make the lights brighten and the car was fine all the way home. Two days later the problem returned.

Tried adding another ground strap but no change.

Battery light and airbag light come on intermittently.

One possibility I read was the fusible link but I haven't been able to find it's location. I thought they were usually in the wiring to the alternator.

I did check that the thermistor at the battery, which the book says measures battery temp, was hooked up correctly.

Any thoughts would be appreciated.

Asinnn wrote:

It's 14.1 disconnected, 13.7 connected. Battery is about a year old.

Normal reading for a fully charged battery is 12.6 volts. With the engine running, the voltage across the battery should be 14-14.5 volts.

not suprising your transmission is unhappy.  it has 4 electrical solenoids in the valve body which
control shifting, as well as a fluid temp sensor.  none of the above would enjoy swallowing 19 volts.

19volts output from any alternator is "over-the-top" excessive.
your system is attempting to cook [burn out] everything,
but,
meanwhile your battery is acting like a sort of capacitor which absorbs the excess while it gets destroyed.
the alternator has a internal electronic voltage regulator which can be replaced.

i'm suspicious of your thermister.
you cannot look at a thermister with your eyeballs and determine if it is working or not.
testing requires a meter, a heat source, and the specs.
[a look at the wiring diagram would not hurt]

if testing is not convenient,
perhaps you could simply try another thermistor and see if the overvoltage gets corrected.
they are not available from GM but they can be had at junkyards, or i can give you one.

you would do well to read the board thread on this subject:
https://rivperformance.editboard.com/t11353p15-thermistor

search "termistor".

i posted regarding alternator problems with my riv and a couple of other members
responded with knowledgable and helpful thermistor posts.
the admin followed my post with a excellent entry on page 2.

studying the factory manual and reading this board got my charging system working correctly
for $5.  
this was after a certified master-mechanic recommended a $150 alternator.

Hi Lance,

Thank you for that comprehensive reply. Your suggestion makes the most sense for the problem. What has been throwing me off is that the last time this happened it was a faulty alternator.

Yes, I have the manuals (and an extra copy of the Electrical section should anyone need it). My mention of the thermistor was only meant to say that it was hooked up. I knew it measured battery temp but not it's full function.

I'll check the connectors and I have a meter so will see about testing it.

Thanks again. My Triumphs have repair manuals that are about 1" thick, my Jeep's is 3", the Buick has two, and the comprehensive one for my recently purchased 98 Mercedes SLK230 is only available online. Time for an electrical engineering degree to go with the tools.

Actually all you probably need to do is replace that *$&@#(^$ thermistor, it should have numbers printed on it (you might need a magnifying glass to see them) and an electronic supply place near you should be able to get you one or an equivalent. There is another thread on here about replacing the thermistor, maybe the admin will point a link to it - I cant seem to find it at the moment. It shows numbers and suggests an electrically compatible but physically more robust replacement. A way to replace it is by replacing the positive battery cable assembly - which can cost you beaucoup bucks - but taking the pos terminal off and opening that shell and crimping/soldering in a new thermistor will cost pocket change and about a half hour.

Without going into mind-numbing detail, what the thermistor does is it lets the alternator run at somewhat higher charging current to accelerate the rate at which the Riv battery recharges... which can help you if you take mostly short trips because without the thermistor permitting the alt to goose the charge the battery won't recharge enough. If your trips are consistently 1/2 hour ( I think) or more at highway speeds it doesn't really matter much.

Albertj

Asinnn wrote:

Hi Lance,

Thank you for that comprehensive reply. Your suggestion makes the most sense for the problem. What has been throwing me off is that the last time this happened it was a faulty alternator.

Yes, I have the manuals (and an extra copy of the Electrical section should anyone need it). My mention of the thermistor was only meant to say that it was hooked up. I knew it measured battery temp but not it's full function.

I'll check the connectors and I have a meter so will see about testing it.

Thanks again. My Triumphs have repair manuals that are about 1" thick, my Jeep's is 3", the Buick has two, and the comprehensive one for my recently purchased 98 Mercedes SLK230 is only available online. Time for an electrical engineering degree to go with the tools.

Hi Everyone,

Thank you for all your help with the Riviera. And a special "Thank you" to Lance. Without Lance's help in obtaining a thermistor, the Riviera would still be parked. Yes, swapping out the thermistor certainly cleared up the shifting issue. Junkyards in my area do not keep complete cars for very long and I had no luck locating a thermistor locally.

This time the only thing affected was the shifting. When the alternator went bad a couple of years ago, shifting, the ac/heater controls and digital readouts on the dash all went haywire.

Attached are photos of the old thermistor cut open to show the internal chip. Unfortunately, it broke in the process. I have tried contacting one Thermistor supplier but it didn't look like anything they offer. He didn't think it was a thermistor at all until I sent him the pages from the GM repair manual. So, finding spares in junkyards seems to be the only solution. I am also attaching another image which talks about testing the thermistor and lists the GM cars that used them.

Very good to know about this problem. It makes perfect sense though, and I'm glad you got it fixed!

Asinnn wrote:

Hi Everyone,

Thank you for all your help with the Riviera. And a special "Thank you" to Lance. Without Lance's help in obtaining a thermistor, the Riviera would still be parked. Yes, swapping out the thermistor certainly cleared up the shifting issue. Junkyards in my area do not keep complete cars for very long and I had no luck locating a thermistor locally.

This time the only thing affected was the shifting. When the alternator went bad a couple of years ago, shifting, the ac/heater controls and digital readouts on the dash all went haywire.

Attached are photos of the old thermistor cut open to show the internal chip. Unfortunately, it broke in the process. I have tried contacting one Thermistor supplier but it didn't look like anything they offer.  He didn't think it was a thermistor at all until I sent him the pages from the GM repair manual. So, finding spares in junkyards seems to be the only solution. I am also attaching another image which talks about testing the thermistor and lists the GM cars that used them.

+1 Thank You to Lance.

For people in the future that have this problem: If you can copy the numbers off of the thermistor body you can replace it using a cross-reference; if you use the info in the Thermistor thread on this site you can get a superior replacement. The replacement does not look like the original all that much... and it does not have to.

Albertj