Hi Scotty,
Our 2008 Cadillac DTS, with 108,000 miles, automatic, has occasional hiccups/misfires. The Blue Driver scanner shows U0100, C0895 and U0140 codes. The Blue Driver scanner says these are fairly common codes for Cadillacs.
As the car seemed to be braking un-evenly, I took it to a local mechanic. He said the brake pads and rotors needed to be changed. He didn't find a misfire in his scanner driving it around. He said that the communication/low voltage codes were pretty much impossible to fix until something actually broke.
The car had new plugs, and 1 new coil installed about 20,000 miles ago at the dealer. 2 years ago the fuel pump and fuse box were replaced, and the battery was replaced when it just wouldn't start.
Blue Driver suggested a few repairs, perhaps a new alternator, BCM or ECM. Other than regular maintenance, the car has not had a new alternator or coils. I am not a fan of throwing parts at cars. I have no idea if replacing plugs, coils, alternator, and two computers will fix the hiccups and computer codes.
Is it time to get rid of this car before it leaves us stranded?
Communications errors are frequently caused by low voltage. Have your battery and alternator load-tested.
I used a Topdon ArtiBattery 101 tester:
Charging High
Loaded 14.56v
no-loaded 14.06v
Ripple Normal
So I guess that alternator and battery are fine.
Battery is 6 months old Interstate from Costco.
SOH 100% SOC98%
12.59V 940A
Int R = 3.18 mOhm
Good Battery
I took it to a local mechanic.... He said that the communication/low voltage codes were pretty much impossible to fix until something actually broke.
well that's simply not true. What he is really saying is "I'm not comfortable troubleshooting even basic electrical problems".
Not a mechanic I would trust.
Is it time to get rid of this car
if that's an option, yes. Caddys are electronics nightmares.
I would still try to fix the issue though. You won't get very much money for a non functioning car
The car had new plugs, and 1 new coil installed about 20,000 miles ago at the dealer. 2 years ago the fuel pump and fuse box were replaced,
these would be my prime suspects. There's a good chance something was damaged or disturbed during this work. Look in the vicinity of these items and look for anything out of place. Chafed wires etc. The fuse box is often located close the the ECM. You can try re-seating the ECM connectors.
Read this document for more tips and things to look for:
So I guess that alternator and battery are fine.
Sounds like it, but load testing with professional-grade equipment would be best. Those inexpensive consumer-grade testers only go so far.
Assuming the battery and charging system are good and those communications codes keep coming back you need to do more diagnostics as detailed below:
https://www.obd-codes.com/u0100
https://www.obd-codes.com/u0140
Note however that the C0895 code does suggest a voltage problem:
https://www.engine-codes.com/c0895.html
This code definition for another GM vehicle states that it is caused by "The control module or sensor detects a system voltage of less than approximately 9 V for approximately 5 seconds" (it is likely similar for Cadillac):