2013 Cadillac XTS, random misfire, random codes from all over the vehicle

I'm hoping somebody will have some tips.
For a few months now my daily driver has had some very random codes. These are almost always accompanied by some misfiring for a while.
I suspect a bad PCM but my next move will be to check all the vehicle grounds. Took it to the dealer but they didn't do much because they couldn't recreate the issues and they were overwhelmed with repair jobs at the time. I don't have a shop in my area with skills like Paul Danner.
Here's the facts:

Bought the car in June with 25,000 miles. Replaced CUE screen (cuescreens.com), new tires, oil changes, air filter, etc.

10/21/2021 40,335 miles
-P0300
-P0304
-U0101 (rear differential clutch & anti-lock brake system) lost communication with TCM
*Read the codes, turned engine off, restarted and everything was back to normal. Did not clear the codes.

10/29/2021 41,221 miles
-P0300
-P0304
-U0101 (anti-lock brake system) lost communication with TCM
-U0401 (anti-lock brake system) invalid data received from ECM / PCM “A”
-U0100 (rear differential clutch) lost communication with ECM / PCM “A”
*Read the codes, turned engine off, restarted and everything was back to normal. Did not clear the codes.

10/30/2021 Replaced the 2013 battery. I hoped this would be the end of the problems.

12/7/2021 45,228 miles
-P0300
*Read the codes, turned engine off, restarted and everything was back to normal. Did not clear the codes.

12/8/2021 45,439 miles
-U0168 (BCM) lost communication with vehicle security control module
-U0401 (anti-lock brake system) invalid data received from ECM / PCM “A”
-U0100 (rear differential clutch) lost communication with ECM / PCM “A”
*Read the codes, turned engine off, restarted and everything was back to normal. Did not clear the codes.

12/31/2021 47,325 miles
-P0300
-P00C6 fuel rail pressure too low, engine cranking, bank 1
-P0113 intake air temperature, sensor 1 circuit high, bank 1
-P2228 barometric pressure sensor “A” circuit low
-C0750 LF tire pressure sensor malfunction
-C0755 RF low tire pressure sensor malfunction
-C0760 LR tire pressure sensor malfunction
-C0765 RR low tire pressure sensor malfunction
-U0168 lost communication with vehicle security control module
-U0401 (anti-lock brake system) invalid data received from ECM / PCM “A”
-U0100 (rear differential clutch) lost communication with ECM / PCM “A”
-P00C6 fuel rail pressure too low, engine cranking, bank 1
-P0113 intake air temperature sensor circuit high, bank 1
-P2228 barometric sensor “A” circuit low
Read the codes, turned engine off, restarted but engine had a significant misfire for several minutes. Did not clear the codes. I was able to make it to my trusted parts store right before they closed (new years eve) and intended to inspect the color of the spark plugs (change them too). Bought a coil pack just in case and because they were closing soon. Engine was running smooth by now. Didn’t have a new gasket for the upper intake so I only had access to plugs/coils on cylinders 5,2,4,6. Traded the coils between cylinders 5&6 and left them that way. Mode 6 data showed misfires on cylinders 1,3,5

1/5/2022 47,469 miles
-Brought the car to Chevy dealer. They couldn’t duplicate the problem, they recommended, and performed a fuel induction system service. They replaced the 2 remaining spark plugs I couldn't do, and intake gaskets for access to the plugs.

1/30/2022 49,446 miles
-PO302
**Read the codes, turned engine off, restarted, code persisted and engine running a little rough. Replaced cylinder #2 coil with new Delphi coil. No change / no improvement. Mode 6 data showing misfire counts growing on cylinder 2

1/30/2022 49,460 miles
-PO302
-PO300
-CO750 LF low tire pressure sensor malfunction
-CO760 LR low tire pressure sensor malfunction
-CO765 RR low tire pressure sensor malfunction
-UO168 Lost communication with vehicle security module
-UO208 Lost communication with “seat control module A”

1/31/2022 49,502 miles
-UO401 (ABS system) Invalid data received from ECM/PCM “A”
-UO100 (Rear differential clutch) Lost communication with ECM/PCM “A”

2/1/2022 No issues since 1/31/2022

Do you know if for say a leasing company, private party previously owned this?

With the low miles it almost sounds as if it sat for quite awhile. Got me thinking if it maybe sat in storage for awhile as rodent damage can definitely cause random issues. Have you went thru and checked harness plugs, etc as just as it could've been a older persons car not driven for awhile it could've been a problem to begin with and just never got looked at, fixed properly.

Seems as if you have some common codes. Is there any freeze frame data so maybe you can replicate the conditions, i.e. what vehicle is doing when this occurs.

Have you checked powers, grounds on the affected components.

Maybe get a one month subscription to one of the DIY repair service information such as all data DIY or another one. The wiring diagrams will be helpful and for the $20 roughly you'll pay it'll be well worth it. If you plan on keeping the vehicle longer then maybe consider a 1 or multi year subscription. I did a 5year on most of my vehicles in the past as for the $40-$50 they charged was cheap compared to dealer labor charges.

If you're having a "lost communication" issue then this could be network related. I'd definitely be looking for some green crusties.

One thing about used vehicles anymore is there's car lots that buy them flooded and anything else after big events such as hurricanes and it's like putting lipstick on a pig as you never know what you're going to get.

It's not all used car places but the ones who do it give the rest a bad reputation.

Dtnel,
I don't know for sure if a leasing company ever owned it but yes, I bought it from a friend (private party) She sold it because they weren't driving it much. It was barely driven for the 4 years they owned it. It was always stored in a heated shop but they are farmers and live down 10 miles of gravel.

I bought the car last July. The problems began in October. Maybe something had finally rubbed through.

There is some evidence a mouse has been on top of the engine/transmission based on nuts and shells in the area. I printed the harness and connector diagrams for the whole car last night and hopefully will be able to inspect all of it this weekend. I only have access to Chilton information through my state library. Subscribing to All Data, etc. is a great idea. Their schematics are likely better than Chilton's. I'll look into those tonight

I have a Uscope, although I don't use it enough to master it. I think I'll start with a visual inspection of harness and connectors. I'll start above the transmission where there is evidence of rodent activity.

Thank you for the tips. It helps guide me in the right direction.

I would suspect problems with one or more data bus -- which could be rodent damage.

FWIW, I wouldn't sweat the U-codes without some other symptoms to go along with them. Are there any warning indicators or messages that come up?

With the misfire codes, I'd be very interested to see what the Freeze Frame and Mode $06 has to say. Tracking the Freeze Frame and which cylinders are favored by the Mode $06 counts may narrow the list of suspects.

No warnings or indicators beyond the usual traction control, stabilitrak lights and the service engine light flashes if the misfire codes pop up. I don't have any freeze frame but was able to save the mode $06 data last Sunday when the cylinder 2 misfire was persistent.

Usually these issues go away by the time I get home or arrive at work. That is frustrating.

I'll attach the full mode $06 report in a pdf file. Here is a summary:

Misfire cylinder 1: 5 counts
Misfire cylinder 2: 468 counts (number was growing even after I swapped the ign coil with a new spare)
Misfire cylinder 3: 2 counts
Misfire cylinder 4: 0 counts
Misfire cylinder 5: 2 counts
Misfire cylinder 6: 1 count

The misfires on bank 2 were a new event. Previously, all the misfires I experienced were bank one, usually one or two cylinders, except for new years eve when 1,3 and 5 were all missing. By the time I turned around and made it back to work (15 miles) everything cleared up.

A visual inspection of the harnesses easily accessible doesn't show any chewed loom or wires. I'm going to take it to work tomorrow so I can start removing things for a better look at the harnesses under the hood, in the wheel wells, under car, etc.

Thank you for the Mode $06 data.

Usually these issues go away by the time I get home or arrive at work. That is frustrating.

So, would it be fair to say that this is a cold engine issue? Or, possibly aggravated by cold ambient temperatures?

With the model year and the mileage, my mind first goes to carbon deposits on the intake valves. Did you happen to take a look at the valves when you had the intake off?

I do live in a cold climate but we have had a mild winter this year. October and November were comfortable (30 to 60 degrees). I commute 63 miles each way and if I had to find any consistency with the problems, they seem to happen 10-15 minutes into my drive.

I didn't have much spare time and decided I needed some help with this so I took it to the dealer Monday January 3rd. They were overwhelmed with workload and didn't spend a lot of time on the issues. They also couldn't make anything fail while it was there.
They pulled the intake and replaced the final two spark plugs I couldn't access (I had purchased the plugs at closing time new years eve & didn't realize the intake would have to be pulled).
They did a BG fuel induction cleaning but didn't tell me if things were carboned up. They did the cleaning because they saw a GM bulletin relating misfires to carbon buildup on the valves.

I'll post a couple pictures/screenshots from my code reader.
When the misfires were on bank 1, I noticed the B1 downstream o2 sensor voltage would drop low on a fairly regular basis. Then when I had trouble with misfires on bank 2, it seemed only the bank 2 downstream o2 sensor voltage would drop low in the same manner. other days both bank 1 and bank 2 downstream sensor voltages would be relatively flat.
I'm not an expert with fuel trims and proper o2 sensor behavior so I don't know if these readings are anything to be concerned about.

I had time today to inspect the harnesses and connectors under the hood including: engine to body harness connector, fuel injector harness, front body harness, power distribution connectors, ABS connector, ECM connectors (all 3) and cleaned all ground studs/ring terminals under the hood. I have some Stabilant 22 contact enhancer and applied that to each connector & ground location.

When inspecting the harness connector inside the trunk I noticed the electronic suspension control module (see pictures) is just laying inside the access panel on a couple red shop towels. That's interesting, looks like somebody didn't mount the module and left the towels there to prevent a rattle.

Behind the battery tray/enclosure the body harness was pinched. I opened up the loom, looked at each wire and tugged each wire to see if there was a break in the copper. Everything appeared fine in that location.

I think all I can do is continue to gather data as it happens and inspect the remaining harness as I have time.

Your fuel trims look okay. What do your both pre-cat O2 sensor readings look like?
Did you look at your wiring diagrams to see if your loss of communication codes are all on the same CAN BUS line?
Have you checked your fuel pressure to verify whether it's in spec? I see one of your trouble codes is indicating fuel rail pressure too low, engine cranking. It might be too low as well when running which could give you misfire codes.
Have you checked power and grounds at the ECM?
Do you have power all of the time at the connectors to the injectors of the misfiring cylinders?

Is the battery in the trunk on these? IF so unplug the battery posts, wait 5-10 min, plug back in and see if anything comes of it.

Had a Cadillac the other day that I could start the car with a non transponder key, unprogrammed transponder key.

Did key relearns, etc and finally to no avail after I was out of solutions I decided to just unplug the battery and wait about 10-15 min.

After unplugging and waiting the time everything worked great again. Sometimes these vehicles are just a little finicky it seems. L

The cylinder with the 2 misfires, I can't recall did you try swapping those (plugs, coils, etc) with known good cylinders and see if it follows or not?

Was there any cylinders leading into the plugs where there may have been oil leaking as I've seen on some vehicles where oil leaking into tubes leading to plugs causes misfires.

I'm sure you don't have this as I think it would've been mentioned by now but just worth noting as anything is possible anymore so we have to think outside the box.

Andy, I spent last Sunday checking connectors and grounds under the hood. I couldn't locate any rodent damage, bad grounds or bad connections, although I can now see I didn't access all of the grounds under the hood. Currently I am working my way through Alldata schematics to see if there is any consistency between specific data bus and codes.

Tyler wrote:

FWIW, I wouldn't sweat the U-codes without some other symptoms to go along with them. Are there any warning indicators or messages that come up?

With the misfire codes, I'd be very interested to see what the Freeze Frame and Mode $06 has to say. Tracking the Freeze Frame and which cylinders are favored by the Mode $06 counts may narrow the list of suspects.

Tyler, I just found a freeze frame report from the December 31 problems. I'll attach it to this reply. The problems that evening were the worst I have experienced so far with this car.
really jumps out at me:
-Bank 1, sensor 2 is showing 99.2% fuel trim
-Control module voltage is 15.2 volts
-Timing advance for cylinder 1 is 42.5 degrees
-About 3 miles down the road I experienced multiple misfires on bank 1 and the long list of codes including two codes for low fuel rail pressure. The freeze frame shows fuel rail pressure at 802.1 PSI.
I'm sure I was pulled over by then and looking at my code reader.

70monte wrote:

Your fuel trims look okay. What do your both pre-cat O2 sensor readings look like?
Did you look at your wiring diagrams to see if your loss of communication codes are all on the same CAN BUS line?
Have you checked your fuel pressure to verify whether it's in spec? I see one of your trouble codes is indicating fuel rail pressure too low, engine cranking. It might be too low as well when running which could give you misfire codes.
Have you checked power and grounds at the ECM?
Do you have power all of the time at the connectors to the injectors of the misfiring cylinders?

I've been checking the fuel rail pressures and although sometimes it's in the 300-400 PSI range at idle, most of the time it is in the 1,600 PSI range while driving. I think these are good numbers for fuel pressure.

The main PCM ground on the engine is clean and tight with a good crimp on it's wire. I have checked most of the grounds and connectors under the hood but today looking at schematics I can see I missed one ground location.

I'm looking at the All Data schematics today to see if the codes are all on the same Bus.

I haven't been able to catch the misfire happening while at home or work and by the time I arrive, the problem goes away. Except for one day I had misfires on cylinder 2 and I was able to put my (new) spare coil on. The misfire persisted for a little while but cleared up while I walked away to grab my Uscope.

Dtnel wrote:

Is the battery in the trunk on these? IF so unplug the battery posts, wait 5-10 min, plug back in and see if anything comes of it.

Had a Cadillac the other day that I could start the car with a non transponder key, unprogrammed transponder key.

Did key relearns, etc and finally to no avail after I was out of solutions I decided to just unplug the battery and wait about 10-15 min.

After unplugging and waiting the time everything worked great again. Sometimes these vehicles are just a little finicky it seems. L

The cylinder with the 2 misfires, I can't recall did you try swapping those (plugs, coils, etc) with known good cylinders and see if it follows or not?

Was there any cylinders leading into the plugs where there may have been oil leaking as I've seen on some vehicles where oil leaking into tubes leading to plugs causes misfires.

I'm sure you don't have this as I think it would've been mentioned by now but just worth noting as anything is possible anymore so we have to think outside the box.

-I haven't disconnected the battery just to reset the ECM but last Sunday I removed the battery to access connectors and grounds under the hood. I had it disconnected for about an hour.

-I had misfires on cylinder 2 and was able to put a new coil on #2 with no improvement. When I walked away to grab my Uscope the problems cleared up. That was the only time this has happened while I was stopped (home or work) and could troubleshoot.

-I know there wasn't any oil inside the spark plug tubes on cyl's 5,2,4,6 but I took it to the dealer and they finished replacing plugs on 1,3. I didn't have an intake gasket so couldn't access 1&3 the night I worked on the other plugs. I hope they would have said something if they saw oil in the tubes. The tech who worked on it is a very good mechanic.

-One thing I can't help but notice is for two weeks I ran premium (91) gas and I had zero problems. I filled up Thursday with regular (87) and within 15 miles I had misfires and a flashing check engine light. By the time I grabbed my code reader the light turned off and everything cleared up. There wasn't
any freeze frame data. I did see PO300, PO306 and B3205, B3210, B3215 (LF, RF, LR, window motor circuit malfunction). I had scanned all modules for codes daily leading up to that and there were no codes at all in the system.
Freeze frame data from 12/31/2021 shows fuel level was 91.4% indicating I had filled up that day too. I always buy my gas at the same place which is 15 miles from where I had trouble 12/31/2021 and last Thursday, 2/10/2022.
That was the third time issues have occured while accelerating on an interstate on ramp.

I really appreciate the suggestions. Eventually I'll get this thing figured out. I suspect a bad ECM but refuse to throw parts at it until I have some evidence pointing towards the ECM.

I just spent 3 months on a 2010 traverse 3.6. 1) throw a used engine module at it, they're cheap, and if that's not the problem, you'll have a spare to try for the next problem that arises. 2) pull the plenum and look at the intake valves with a harbor freight borescope, if you don't have one. I promise you the valves will look like crap even after the bg service was done. 3) do an injector balance test to see if cylinder #2 is flowing less than the others. Good luck.

Tyler, I just found a freeze frame report from the December 31 problems. I'll attach it to this reply. The problems that evening were the worst I have experienced so far with this car.

Good stuff, thank you!

-Bank 1, sensor 2 is showing 99.2% fuel trim
-Control module voltage is 15.2 volts
-Timing advance for cylinder 1 is 42.5 degrees

All of these are pretty normal, for a variety of reasons. The fuel trim values you see for downstream O2 sensors (O2 Bank 1 - Sensor 2 - Short Term Fuel Trim and O2 Bank 2 - Sensor 2 Short Term Fuel Trim) are completely irrelevant and should be ignored. The value of 99.2% the scanner is reporting is a placeholder value, not an actual indication of fuel correction.

Newer GM's will sometimes charge up to 15.5V if the BCM thinks it's appropriate.

That much spark timing advance on a hot restart with a raised idle isn't unusual.

-About 3 miles down the road I experienced multiple misfires on bank 1 and the long list of codes including two codes for low fuel rail pressure. The freeze frame shows fuel rail pressure at 802.1 PSI.

That's interesting. :blink: I'm honestly starting to wonder if you have a fuel injector that's leaking down or otherwise sticking open intermittently. That might explain the low fuel rail pressure codes and the misfires.

-One thing I can't help but notice is for two weeks I ran premium (91) gas and I had zero problems. I filled up Thursday with regular (87) and within 15 miles I had misfires and a flashing check engine light. By the time I grabbed my code reader the light turned off and everything cleared up. There wasn't
any freeze frame data. I did see PO300, PO306 and B3205, B3210, B3215 (LF, RF, LR, window motor circuit malfunction). I had scanned all modules for codes daily leading up to that and there were no codes at all in the system.
Freeze frame data from 12/31/2021 shows fuel level was 91.4% indicating I had filled up that day too. I always buy my gas at the same place which is 15 miles from where I had trouble 12/31/2021 and last Thursday, 2/10/2022.
That was the third time issues have occured while accelerating on an interstate on ramp.

I noticed the same thing in the Freeze Frame data you posted. Sticking purge valves are very common on this engine, and can definitely cause misfiring on startup after refueling. The Commanded EVAP Purge and the EVAP Vapor System Pressure don't suggest an issue, BUT I've learned from experience that the Vapor Pressure PID in Mode $02 usually doesn't work correctly.

How full is your tank right now? If it's less than half, I'd suggest refueling and going for a test drive. If you immediately start having problems, we're onto something. If not, hey, at least you've got a full tank.

ProAuto,
I'll take your advice and order a used ECM tonight. I've reached that point.
I spent a few more hours on it today checking a couple grounds I had missed last time and also checking the contacts in the 3 ECM connectors. Took it for a drive and had 3 new pending codes show up (MAP sensor, IAT sensor and barometric sensor).

The misfires codes have moved cylinders a lot and the one time I was home while it happened I swapped for a new coil with no improvement. I don't have a borescope and HF is sold out. I'll borrow one from our NAPA store this time and see how things look. It is something I should do from time to time to keep an eye on the carbon problem these engines have.
Thank you for your help.

Make sure you get the ecm programmed if you can prior otherwise make sure you have the proper equipment for when you do it. Have you swapped any electric parts on this vehicle lately that maybe weren't mentioned here?

Did you try disconnecting the battery cables, letting it sit 10-20 min to see if maybe the computer needs to refresh itself?

I can't recall if I'd mentioned but I recently had a '12 CTS 4 door I did a key & remote on with a ton of codes. Disconnecting the battery helped. As a matter of fact I have to drop keys by car dealer tomorrow so can get paid. They're not going to like the fact that the remote start & trunk don't work and this is a OEM replacement remte.

I called the dealership and they said this was a remote start vehicle from the factory, lights for remote start and trunk button flash but they don't work but they cause the taillights to flash when button is depressed so it's getting communication so it shows the remote is communicating properly with the car RKE system.

I have the proper remote as well as the dealer gave me the part number. There's probably something wrong with one of or both of the systems that aren't working. We'll see soon enough. Don't think they want to pay me the extra $80-$100 for diagnostic so I'll drop my keys & move on after I get my cash / check