1991 Cadillac Deville Digital fuel management display

Tiny
WU3G5H2Q
  • MEMBER
  • 1991 CADILLAC DEVILLE
  • V8
  • FWD
  • AUTOMATIC
  • 79,000 MILES
My wife has a 1991 Cadillac that she inherited from her mother. It only has 79,000 miles on it.
The problem is the onboard fuel management digital display on the lower LH side of the dash.

For months now the display has been blank like it has no power to it. Periodically we will start the car and the display will come on and it will function propery until it goes blank again just like you turned the key off. The local Dealer said it coud be the sending unit in the gas tank is failing. I have found no loose connections under the dash to the unit and am wondering if it could be the fuel pump/sending unit in the gas tank. Hate to replace the fuel pump if that's not the most likely culprit.
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Friday, October 22nd, 2010 AT 2:46 PM

4 Replies

Tiny
KHLOW2008
  • EXPERT
Hi wu3g5h2q,

Thank you for the donation.

Problem is not likely to be the fuel sending unit. If that is the case, the Fuel Data Center (FDC) would still illuminate.

Probable cause would be a fault with the FDC or its wiring and other communications. A loose connection is quite likely to be the cause.

FUEL DATA CENTER CONNECTOR TEST

1. Disconnect fuel data center connector. Turn ignition switch to RUN position and turn parking lights or headlights on.

2. Using a voltmeter, measure voltage between terminal "L" (Brown wire) and ground. If battery voltage is present, go to next step. If battery voltage is not present, check Brown wire for an open circuit, and check instrument panel fuse No. 7.

3. Measure voltage between terminal "P" (Orange/Black wire) and ground. If 16 volts are present, go to next step. If 16 volts are not present, check Orange/Black wire for an open circuit. If wire is okay, Powertrain Control Module (PCM) and Body Control Module (BCM) diagnosis is necessary.

4. Measure voltage between terminal "T" (Tan wire) and ground. If 5 volts are present, go to next step. If 5 volts are not present, check Tan wire for an open circuit. If wire is okay, BCM/PCM diagnosis is necessary.

5. Measure voltage between terminals "L" (Brown wire) and "M" (Black/White wire). If battery voltage is present, go to next step. If battery voltage is not present, check Black/White wire for an open circuit. Ensure grounds are clean and tight.

6. Measure voltage between terminals "L" (Brown wire) and "S" (Black/White wire). If battery voltage is present and ECC display is normal, replace fuel data center. If battery voltage is not present, check Black/White wire for an open circuit.
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Sunday, October 24th, 2010 AT 1:43 AM
Tiny
WU3G5H2Q
  • MEMBER
I'm going to work on the car this weekend. Any chance you have/can send a simple wring diagram that shows the location of grounds etc for this fuel data center/

Thanks
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Friday, November 5th, 2010 AT 12:12 PM
Tiny
KHLOW2008
  • EXPERT
Sorry I could not find any diagrms showing the location. The only information on the grounding circuit for the FDC are :

Terminal "M" Black wire, ( ground ).

Terminal "S" black/Yellow wire ( REF Ground ).


http://www.2carpros.com/forum/automotive_pictures/192750_FDC91DEVilleFig07_1.jpg

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Friday, November 5th, 2010 AT 12:43 PM
Tiny
WU3G5H2Q
  • MEMBER
Thats perfect. Thanks

I'll let you know what I find.
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Friday, November 5th, 2010 AT 5:23 PM

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