CHARGING SYSTEM

Tiny
112652
  • MEMBER
  • 1999 CADILLAC EL DORADO
  • V8
  • FWD
  • AUTOMATIC
  • 130,000 MILES
HOW DO I TROUBLESHOOT CHARGING SYSTEM ON A 99 CADILLAC ELDORADO? I HAVE INSTALLED A NEW BATTERY, CHECKED PCM FUSES BOTH ARE "OK", WITH ENGINE RUNNING VOLT OUTPUT TO BATTERY IS 11.5 VOLTS, "NO" DIAGNOSTIC CODES.
THANK YOU FOR YOUR ADVICE.
RON
Do you
have the same problem?
Yes
No
Thursday, April 21st, 2011 AT 11:06 PM

4 Replies

Tiny
CADIEMAN
  • MEMBER
Have the charging system checked at auto zone.A quick way to check your alt. Is to remove the neg. Cable at the battery with engine running. If it cuts off the alt. Is bad. 11.5 is not enough voltage. You still need to check the starting and chargeing voltages as well as load test the battery and also check for a draw. Gl
Was this
answer
helpful?
Yes
No
+2
Friday, April 22nd, 2011 AT 12:13 AM
Tiny
CARADIODOC
  • EXPERT
Measure the voltage on the output wire and the red small wire plugged into the side of the case. If you have battery voltage, (11.5 volts) on the output terminal, that circuit is okay. There should be around 2.0 volts on the small wire if the battery light is on. That is the turn-on signal for the internal voltage regulator. If both of those voltages are there, replace the generator.

These are a real poor design and it is common to go through four to six of them in the life of the car. What many professionals are finding out is to reduce the repeat failures, replace the perfectly good battery, as you already did, at the same time. As they age, they lose their ability to dampen and absorb the huge voltage spikes these generators produce due to their design. The old battery will work fine in a pre-1987 vehicle.
Was this
answer
helpful?
Yes
No
Friday, April 22nd, 2011 AT 12:16 AM
Tiny
CARADIODOC
  • EXPERT
AAAGGGGHHHH! DO NOT REMOVE THE BATTERY CABLE! That was a trick done many years ago by people who didn't understand these systems. There is less than 13.75 volts so you know the generator is not working. Except for the fuse, (voltage at the output terminal), there's nothing left to test.

AC generators by their very nature produce "ripple" even though it is rather low because it's a three-phase output. That ripple is detected by the voltage regulator and is applied right back to the field winding. The rise in voltage makes a bigger electromagnet which raises output voltage. The viscous cycle continues and the regulator can not control it. I did this every year to show my students what happens. The only thing that saved some generators from self-destructing their diodes and regulators was the test bench only had one speed. When I did that on a car and raised engine speed, it was real common for the system voltage to go over 30 volts. That will destroy any light bulb that is tuned on and can damage multiple computers. Every year I sacrificed one generator by doing that demonstration.
Was this
answer
helpful?
Yes
No
+4
Friday, April 22nd, 2011 AT 12:26 AM
Tiny
CADIEMAN
  • MEMBER
If the alt. Is not charging right. The bridge, diode and brush pack needs to be replaced. Unless u buy a complete alt. Gl
Was this
answer
helpful?
Yes
No
+2
Friday, April 22nd, 2011 AT 1:22 AM

Please login or register to post a reply.

Recommended Guides