Hi everyone!

This is my first post and I hope this info helps someone. Recently my 98 SLS instrument panel produced several messages: battery voltage too high (or some such), service ABS, service security system, service traction control system, etc., etc... I scanned through the dash menu to the battery volts. The reading was too high at >17v. Not good!

Now, from many years of experience with typical charging systems, this symptom points to a bad voltage regulator. So, fairly convinced of the diagnosis, I removed the alternator. Wanting to replace the regulator, as well as the bearings/bushings/brushes, myself, I called the parts house. No regulator listed. Wah! Called the dealer - no listing. But they will sell me new alternator... For $750.00!!!!!!!!!!!!!!!! Double Wah!! Called a friend who rebuilds alternators, generators and starters. He says he thinks he has the regulator in stock. Score! Replaced regulator, bearings & brushes for $150.00. So far, so good.

Installed rebuilt alternator. Still reading >17v. Triple Wah!!! Busted out the factory service manual <-- these are priceless, guys! Ten minutes into scanning the wiring diagrams for anything connected to the alternator that I don't recognize, I find reference to a thermistor. Located on the end of the positive battery cable, at the battery, the thermistor, according to said manual, provides a variable resistance to the PCM, which then uses the info to control how much juice the battery gets. Interesting! So, does the manual tell me how to test this variable resistor? Yes and no...

In the diagnostic table it tells you to disconnect the thermistor - connector is a mere 5 inches from actual thermistor - and measure resistance across both leads of the sensor. The problem? In the little box in the table of the service manual reserved for the desired measurement reading is... Nothing! Empty!! No entry!!! Seems they sorta forgot to enter the number ~ 5 ohms, 500 ohms, 5 megohms... you get the idea. Quadruple Wah!!!!

Starting at the beginning of the section on engine electrical, I scan every page; maybe there's another reference to said sensor, with perhaps the missing required resistance. And Aha! There it is!! 5 ohms. Measured the resistance at ~ 4k ohms. Not good!

A call to the dealer reveals the part is on back order. Oh well, it lists for about $35.00 anyway. I happened to have a 10 ohm resistor on hand, so I hooked that up and tested. Success!!!!!!! Only the volts are still a tad high at 14.9v. Should be between 13.8 & 14.2 - ideally. I'll take a drive to Radio Shack tomorrow and pick up a 5 and a 15 ohm resistor. Theoretically, one will raise the voltage higher and one will lower it. Theoretically...

Hope this helps somebody.

Vince

Good catch, Vince. Yes, you want the cruise charge to float around 14.1 - 14.3 VDC, hoping the voltage regulator is ramping down amperage as the battery reaches full charge.

I am running 14.6-15.1 most times that I check the voltage. The computer says this is still in the acceptable range. I have only had one electrical gremlin that may have been associated to the battery though. After I washed the car with doors open for a long period, upon start up it read "service theft system" or something like that. However, that went away on the next start up and has never returned and only got the error code for high voltage once. Should I be worried about 15+v??

As Vince posted, the sensing thermistor controls final output voltage based on temperature. Wait until warmer weather and see if your average voltage, on the road, doesn't drop to around 14.2 - 14.4 VDC.

Ahh, the THERMistor.

ok
i REALLY
REALLY
like this guy
not only does he 1st buy an FSM, but he actually uses it and tried to generate answers to his own problems without coming here 1st
what a great example of a new member who is truly going to be a GREAT asset to the community!!!

that said hes a few things to check
while your intial diagnosis was a great one, have you tried actually running the on board diagnostics of the car?
If you havent figured out how to do it, or dont know how ususally id say search but since youve already done a GREAT amount of that here you go, your in for a real treat. Press and hold on the right side of the cluster buttons the INFO ^ and the ON/OFF button for about 5 seconds, after which the car will light up like a friggen XMas tree. Cycle through with the Info ^ or v and select what is appeared on the DIC with the ON OFF button, to exit press the middle RESET button a few times to back up and out of the system. Use the INFO to select CODES then ALL CODES, at which point the car will then display ALL codes stored in the system, both history and current. Copy them all down ESPECIALLY the current ones, and bring them back here for futher diagnosis.

Both my (previous) '02 SLS and my '03 DHS run 15+ (most of the time).

....Starting at the beginning of the section on engine electrical, I scan every page; maybe there's another reference to said sensor, with perhaps the missing required resistance. And Aha! There it is!! 5 ohms. Measured the resistance at ~ 4k ohms. Not good!

A call to the dealer reveals the part is on back order. Oh well, it lists for about $35.00 anyway. I happened to have a 10 ohm resistor on hand, so I hooked that up and tested. Success!!!!!!! Only the volts are still a tad high at 14.9v. Should be between 13.8 & 14.2 - ideally. I'll take a drive to Radio Shack tomorrow and pick up a 5 and a 15 ohm resistor. Theoretically, one will raise the voltage higher and one will lower it. Theoretically....
If the resistance reference you found did not include a temperature value, you were looking at something other than the thermistor resistance/temperature specification.

The theoretical and applied purpose of a thermistor is to provide a sense of ambient temperature input to the system.

The thermistor in my '98 Seville measures 1,590 Ohms at 71 degrees F. Depending on temperature, I would expect you would be far outside the acceptable range of resistance values when you substitute a 5 or 15 Ohm resistor for a specific thermistor.

My electrical system (battery, alternator and all modules) continues to be perfectly happy with the performance of my charging system (and thermistor) at 170,xxx miles.

whats the point of a thermisistor in these cars is beyond me?

:stirpot: Crown Vic........There are 8 thermistors (temperature controlled resistors) in a '98 - '04 series Seville. 4 in Engine Control/Electrical systems, and 4 in Body Control/HVAC.

Find 'em and describe their function. All in the FSM, Alldatadiy, and these Forums.

Hi everyone!
Sorry I haven't gotten back here sooner. As promised, I bought a 5 and a 15 ohm resistor at RS. The 15ohm unit didn't change the voltage displayed on the dash, but the 5ohm did. It dropped it to 14.7v. I'm happy with that and so is the computer. Someone asked about acceptable battery charging voltage; 14.7 volts is as high as I'd like to see. The reason; as voltage climbs above 15 or so volts the battery acid begins to boil out of the battery. When I bought this car 3 1/2ish years ago, the floor around the battery was pristine. After the little thermistor failure, the paint around the battery began to peal. I used baking soda and water and neutralized the acid, then used a spray can of battery protectant from Walmart to spray the affected area. Good to go, now.

JimD,
Don't remember the exact page or section of the FSM that referenced the thermistor resistance value but it is there. In ohms. It tells you to disconnect the thermistor from the harness and measure resistance across the thermistor. Should be ~5ohms. Mine was 4.3kohms (4,300 ohms). Bad thermistor. As stated, since replacing thermistor, no more error codes and the car runs good.

Good day!

I think I sent JIMD an email when I got my 2001 Deville. Just to check..

I could at times display 14.6-15 on volts. Hmmm. Seemed kinda high..

JimD reported the same exact numbers. 3-4 years later. No problems so far.



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Output is considered normal if in a range between 13.2 and 15.9. The codes are not set until over 16 or less than 11 volts. My STS averages 14.9, going sometimes to 15.7 depending on load, it has done this since new with no problems.