Cadillac Repair: 91 Deville Fuel Data Center Problem..., dielectric grease, connector pins

Question
Bill,

I am  retired and have a super clean '91 Sedan Deville  that I absolutely love...!

However, recently the fuel data center began acting up...changing display modes by itself...then acting normally again.

On several occasions the FDC would show the gallons of fuel in the tank, but the real time MPG and Average MPG would default to "0.0 MPG"

Now...the screen remains blank with a small letter "d" where the gallons is normally displayed. After 2-15 mins driving the "Service Engine" light comes on followed by the "Check Engine" light.

Once in a while, the blank "d" screen will display all functions correctly for a few seconds...only to  revert back to the blank "d" screen again.

The codes in the diagnostic check are E47 and F32 indicating data problems between the PCM / BCM.

Drivability of the car remains normal, except that the A/C compressor goes off line whenever both Service/Check Engine lights come on.

Do you think the FDC should be replaced as a start?

Or...would you just check all ECM / PCM connections, possibly adding some dielectric grease to the connector pins?

Be advised that I have a "good" used FDC (# 1228851) being shipped to me as an alternate for test.

In checking the service manual, circuits 719 and 526 would appear to be likely culprits if grounded or open. However, I am NOT looking forward to tracing individual wires wrapped in taped bundles under the dash, while upside down on the floor board...! Only as a last resort, as my old body is not as flexible as it used to be.

I can clear the memory and repeat the same error codes within a 30 min. test drive, however on some occasions only the F32 code is present.

Also, the Climate Control Data Center acts normally at all times. The "d" ONLY shows up on the Fuel Data Center.

Any and all help is appreciated. The more detailed...the better.

Thank you for your service.

Kerry  

Answer
Hi Kerry, Sorry I didn't get back to you sooner but your problem needed more research. According to the Caddy shop manual they want the display panels unplugged and switched. So plug the FDP into the ECC connector and the ECC into the FDC connector. If the FDC still shows a d then replacing the panel should fix the problem. If the ECC shows a d then there is an open or short to ground in ct719 or a faulty BCM connector or faulty BCM. So its quite possable that the FDP is bad but I wouldn't plug in the replacement FDP yet or get it from the parts store until you switch the panels to the other harness connector and confirm that the problem stays with the panel. Let me know if you need more help. Bill