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Alexandra - 96 SDV Clyde - 15 Silvy
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6,394 Posts
Discussion Starter #1
1996 Sedan DeVille

VIN Y

92,800 miles

Problem: Voltage drops when I brake

Description: She loses voltage when I hit the brakes. Voltage is 12.6 volts with the key ON, Engine OFF, and accessories OFF. Voltage when vehicle is less than operating temp (196F) is 14-14.1 at idle, stopped, 13.9-14.1 when vehicle is moving and gas pedal is depressed, and 13.0-13.3 when brakes are applied. After vehicle comes to a stop, the voltage rebounds.

When she's at operating temp, voltage is generally 13.7-13.9 at idle, though it will occasionally drop into the low 13's before rebounding. 13.7-13.9 when vehicle is moving and gas pedal is depressed, and 12.5-13.1 when brakes are applied. When she stops the voltage will rebound to 13.4, and will not increase until acceleration occurs.

Codes:

PC0231 - HISTORY - Fuel pump volts low-I pulled the pump fuse to change the filter in hopes of not spilling so much gas

PC0603 - HISTORY - Long term reset -Disconnected the battery during alt replacement (More on that later).

RS0011 - HISTORY - LF Damper solenoid valve short to ground - Passive struts installed. Attempted wiring in 4.7K Ohm, 1/2 watt resistor to eliminate SERVICE RIDE CONTROL message. Used butt connectors but crimped with needle nose pliers. Will reattempt as wires may have been dirty.

RS0012 - HISTORY - LF Damper solenoid valve open circuit - See above.

RS0017 - HISTORY - RF solenoid valve open circuit - See above.

RS0026 - HISTORY - RF Damper solenoid valve short to ground - See above.

Recent work done

Alternator is Denso remanufactured unit specified for 1996 Cadillac Sedan DeVille VIN Y. Unit first installed in vehicle 3/20/2015.

Serpentine Belt is Gates unit specified for above vehicle. Unit first installed in vehicle 4/8/2015.

Serpentine Belt Tensioner is Gates unit specified for above vehicle. Unit first installed in vehicle 4/8/2015.

Idler Pulley is Gates unit specified for above vehicle. Unit first installed in vehicle 4/8/2015.

No recent brake work. Last brake work 8/2012 for replacement of pads and rotors.

Left front high beam, left front inner turn signal, and left side rear quarter panel marker connectors sheared off in accident on 1/10/2014. All exposed wiring cleaned with isopropyl alcohol, wrapped in electrical tape, and then wrapped in gorilla tape.

Possible 5/16 socket in engine bay. Did not previously create any problems.

Serpentine belt tension is tight.

Battery is Diehard unit specified for above vehicle. Unit was tested on 3/20/2015 and tested good. Unit was fully charged on 3/20/2015.

Battery connections are clean and tight.

Any ideas? Am I worrying over nothing? Please help. I am frustrated. Thank you.

P.S. On the bright side, the squeal heard on 1-2 upshift disappeared. Guess my belt was previously too loose.
 

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2011 DTS Premium w/1SD | 1999 Deville Base (RIP @179K Miles)
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404 Posts
Are your battery terminals clean?

Check the brake switch to see if the wires have been tampered with.

Also check the light bulb sockets to see if they have corrosion on them.
 

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1979 Coupe deVille, 1995 Sedan DeVille (sold)
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1,846 Posts
Does the voltage drop vary with the severity of the braking?
Does it still happen if the car is stopped (parked?) and you press the brakes?

I see you changed the struts to passive. Have you tried having someone push down on the front of the car while running and see if it happens then?
 

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Alexandra - 96 SDV Clyde - 15 Silvy
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6,394 Posts
Discussion Starter #4
Terminals are clean, though the positive cable has a possible cut. That is in the process of being replaced.

I will check the brake switch, though I can't think of anybody who would have been in the car.

The left brakelight harness is a good place to check for issues, so I will do that.

Voltage drop seems to be more significant at lower speeds and with more braking effort.

I was monkeying with the brakes when I jumped in today after clinicals. It does seem that, with the car in park, when I hit the brakes, the voltage does drop, though not as bad as when she's rolling (drops to 13.5-13.7 when stopped).

I haven't tried somebody pushing on the nose, but that's worth a shot. I am also planning on revisiting my wiring and using a crimper this time, as well as cleaning the wires well.

Thank you guys. I really appreciate it.

EDIT: FWIW My resistor wiring is NOT currently functional. I still get SERVICE RIDE CONTROL after going over a harsh bump.
 

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Alexandra - 96 SDV Clyde - 15 Silvy
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6,394 Posts
Discussion Starter #5
Tail light harnesses checked out. The trailering wiring in the trunk also checked out, so that rules that out.

Something else I noticed, braking while parked results only in sporadic voltage drop.

The hunt continues.
 

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1996 sedan deville
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188 Posts
You might be chasing your tail. My 1996 has been doing the same thing since I got it. I quit watching the voltage gauge.
 

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Alexandra - 96 SDV Clyde - 15 Silvy
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6,394 Posts
Discussion Starter #7
I know :( I am considering that may be the issue. If new battery cables and a reattempt at my resistor wiring doesn't work, then I may wait until I graduate. Then I can invest more time into it.
 

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Alexandra - 96 SDV Clyde - 15 Silvy
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6,394 Posts
Discussion Starter #9
For what it's worth, I fixed the issue. Turns out it was a combination of a bad alternator (voltage drop under additional load) and a faulty battery (low voltage when vehicle is at operating temp). Other contributing factors include a Delco tensioner and idler pulley.
 
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