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1997 Deville d'Elegance
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Discussion Starter #1
Hey all,
I have a 1997 Cadillac Deville d'Elegance with a couple issues. i'd like to say I've enjoyed my experince with the car but so far it's been a bit of a pain. A bit of backstory on the car: we picked it up from my grandfather when he traded up to a DTS a couple of years ago for the purpose of transporting my now 94 year old grandmother around. It's the only car in our fleet that is low enough for her to get in and out of with ease. It had a hard life before we got it as it wasn't really maintained and has since had a series of issues since we've gotten it, most have been fixed at a mechanic:
  • Cracked starter motor shaft
  • Cracked coolant reservoir
  • Leaking coolant radiator headers (the plastic part crimped onto the inlet and outlet of the metal fin section)
  • Bad alternator that somehow provided almost no current at resting RPM but still maintained voltage)
  • Busted vacuum diaphragm in the fuel regulator
  • Worn belt tensioner
  • Dead turn signal flasher
  • Worn upper motor mounts
I have a series of issues occurring at the moment, some of which are throwing the SES light and another which is not.

Issue 1
The first is three DTCs: P0171, P0174, and P1645. Pretty sure these are related. Any thoughts on how to resolve these DTCs?

Issue 2
The second issue is more concerning. Since the alternator incident (where the car cut out on me while driving with no warning), I've had the display set to show the battery voltage. Over the past couple months, it's started this issue where the voltage (read from the display) will decrease over time. When the issue started, it would decrease from ~14.3V at engine startup down to ~12.7V in lower speed driving. Hitting the gas and revving the engine would generally convince it to come back up. to ~13.7V. More recently, the startup / high speed voltage has been no more that 13.3V decreasing to ~12.2V, and in some cases to the lowest extreme I've recorded of 11.8V. In cases of low voltage, the speedometer will read bogus numbers, the traction control has been known to turn off, a theft system problem will display, and in one case, the ABS light came on. I had taken the vehicle back to the mechanic who installed the alternator shortly after I noticed the issue saying it was functioning correctly. Weirdly, turning the vehicle off and the on jumps the voltage back up to ~13.3V.

I'm borrowing an multimeter from a friend tomorrow to check voltage at the battery at startup and after driving to see if the display readout is correct. Any thoughts on this issue?

Thanks all in advance for any information / solutions you can provide.
 

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98 DeVille, 97 DeVille d'Elegance
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7,345 Posts
You have a vacuum leak causing the lean codes. May very well be related to evao code.
Alt voltage normal. You may have a bad ground at frt of engine, known to get corroded and need cleaned and will cause all kinds of issues.
Anyways... Welcome to forums.
All those items you've fixed are normal, i would add on changing the frt lower motor mount. When the dog bones wear out its because the lower mount is shot(very common issue).
 

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1997 Deville d'Elegance
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2 Posts
Discussion Starter #3
Hi rodnok01, thanks for the reply and welcome.

I figure I'll see if replacing the EVAP solenoid fixes the lean codes though I wouldn't be surprised if there's another location. Some more recent research has shown that the connection between the inlet manifold and throttle body is a hot spot for leaks. I guess I'll cross that bridge when I get to it. I was trying to locate a diagram of the vacuum system but was unable to find anything. Do you know of any resources that would display this information?

I looked at the battery voltage with a multimeter and the display voltage seems to be 0.3V lower than the multimeter. I'm not sure a grounding issue seems likely to me as it only seems to happen after the car has been running for a bit and during low MPH driving / stops. Regardless, it can't hurt to look into this. I'm having similar issues locating documentation to point me in the right direction to find the grounding locations. Can you provide any assistance to finding these points?

Thanks for your help and time!
 

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98 DeVille, 97 DeVille d'Elegance
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7,345 Posts
Hi rodnok01, thanks for the reply and welcome.

I figure I'll see if replacing the EVAP solenoid fixes the lean codes though I wouldn't be surprised if there's another location. Some more recent research has shown that the connection between the inlet manifold and throttle body is a hot spot for leaks. I guess I'll cross that bridge when I get to it. I was trying to locate a diagram of the vacuum system but was unable to find anything. Do you know of any resources that would display this information?

I looked at the battery voltage with a multimeter and the display voltage seems to be 0.3V lower than the multimeter. I'm not sure a grounding issue seems likely to me as it only seems to happen after the car has been running for a bit and during low MPH driving / stops. Regardless, it can't hurt to look into this. I'm having similar issues locating documentation to point me in the right direction to find the grounding locations. Can you provide any assistance to finding these points?

Thanks for your help and time!
DIC voltage and multimeter voltage seldom will be exactly the same, I've messed with it myself and it doesn't read the same. I wouldn't worry about the difference.
Fsm, Alldata or Mcnally website(dealer) for vac diagrams. These years don't have a plenum to rip as the later years. For these check pcv grommets in cam covers and associated lines especially where connect to TB area. Another common leak area is the lines running into the cabin. They rot out between engine and behind pass strut area. When these go bad parking brake won't auto release and inside hvac controls get sluggish or flaky.
Last place can be the over pressure valve at end of intake can stick causing massive leaks(not really that common of issue). I bet yiu find a line cracked of off somewhere.
As for grounds there are a ton... Main is frt engine near battery, there are couple each side rad support, behind engine near trans /engine area. Inside grounds are: 2 on pass kick panel, 1 drivers kick, 3 behind and under fear seat plus under drivers seat(abs module ground). There are others in trunk and others I haven't listed such as EBCTM ground and ICM specific ground.
These are overly picky about power and especially grounds, anytime you have an electrical issue start with them as it fixes a lot of problems.
 
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