Have been experiencing the well documented fuel sensor problem for about 3 months now. More recently the engine just stalls out while under power as if it is running out of fuel. (Tank is full of fuel). So far it has restarted everytime. But I suspect there will come a time when it won't. ie total failure of whatever is failing. My question - could this be related to the sensor problem or a different fuel pump issue. If I have the sensor replaced would it be smart to replace the fuel pump as well?

Pull the DTC's. If it is a sensor it will set and store a DTC. Sounds a little like a CKP sensor. Possibly a failing fuel pump. If not codes stored, I'd check the fuel pressure.

You need to pull the Diagnostic Trouble Codes from the car's built-in scanner/reader system. A complete engine stall or even a miss will set codes and give you a troubleshoot path.

Read the entire sticky thread on code pulls at the top of the main Deville page........

Thanks for the tip about reading the codes. I pulled the codes and here is what I found.

ABS C1287 History - Steering Sensor Rate Malfunction
AMP U1128 History - Loss of Communications with IRC
DDM U1714 History - Loss of Front Door Module to Window Motor Normal Speed Comm
DIM U1016 History - Loss of Communications with PCM
IPM B0429 Current - Temperature Control #3 Rear Circuit Range/Performance
IPM B1004 History - Keep Alive Memory (KAM)
IRC B1328 History - Vehicle system voltage is greater than 15.9 volts
MSM B2365 History - Driver Rear Vertical Sensor Malfunction
PCM P0463 History - Fuel Level Sensor Circuit High Voltage
PCM P1106 History - Manifold Absolute Pressure (MAP) Sensor Circuit Intermittent High Voltage
PCM P1617 History - Engine Oil Level Switch Circuit
RFA C0760 Current - Tire Pressure Monitor (TPM) system sensor not transmitting

Only 2 current ones. And suggestions as to why under power just cruising alone the engine stops running. (Like it has run out of gas). Has happened twice in two days.

Dollars to doughnuts one or both CKP's (CranKshaft Position sensors) is getting ready to pack it in. You should start seeing codes P0335/6 and P0385/6. The most typical symptom is a slow speed stall, stall at stoplight, or stall during transition from closed loop (warmup) to open loop emissions and management status. The engine quietly shuts off and will do an immediate restart, maybe setting a voltage or "try to start in gear" code.

Do you live in an emissions test area and are you due for a test ? If not, get back into the code reader sequence and, at the end of the code string readout you will be asked "Clear codes ?" Answer YES, clear all codes, and turn the key OFF. Cross your fingers (stall-wise) and drive for a few days. Read the codes again to see what has popped up: A code will set if a fault occurs and will remain as Current until 3 start-run operations during which the fault does not occur when it goes to History where it remains for 30, 40, or 100 successful cycles and then self-clears.

B0429 is the rear seat air diverter actuator, down on the right side of the HVAC airbox over the passenger's left foot. It feeds the little panel on the rear of the console.

C0760 is probably a TPMS wheel sensor lithium battery. Not uncommon.

The rest are History, so log them all with the date, clear codes, and start over.

Dollars to doughnuts one or both CKP's (CranKshaft Position sensors) is getting ready to pack it in. You should start seeing codes P0335/6 and P0385/6. The most typical symptom is a slow speed stall, stall at stoplight, or stall during transition from closed loop (warmup) to open loop emissions and management status. The engine quietly shuts off and will do an immediate restart, maybe setting a voltage or "try to start in gear" code.

That is exactly what happens, the motor just quietly shuts off. It restarts just fine. I had a quick look at some parts stores and see the replacement Crankshaft Position Sensor cost is reasonable. Are they difficult to replace? Or require special tools / equipment? Almost looks like it is plug and play......

For your car the new series of CKP is made in Japan, probably by DENSO. One is gray, the other black. The faulty (early mortality) group was made in Mexico by Siemens, one tan, one black. They're up on the side of the block just to the right of the oil filter adapter, two Hall effect sensors which send crank rotation position to the PCM ignition trigger. You need to get the car up on a hoist, pull the front splash shield, mutter magic words while disconnecting the electrical connectors (snap locked), and removing the 10mm bolts. 99.9% of the time you don't need to do a "CKP Relearn" procedure: dealer, 1 hour charged, which resets any minuscule timing angle differences in the new sensor(s).

Look at www.rockauto.com or call Luke at Lindsay Cadillac (parts) over there >>>>>>>>> M-F, 9-5, EST.