CEL U0073 Causes

[Daskuppler]

Hello everyone!

Me again... yet more problems... 2014 Forester Premium, 141k, with CVT.

 

We took a short drive this morning (90 minutes, 70 miles) and parked the car to wait for the sunrise. When we started the car, the CEL came in and the cruise control light started flashing. There were no driveability issues, but we never got over 20mph. After restarting the car, the CEL was gone and hasn't come back. When I got home, there was one stored code for U0073: control module communication bus A off.  Code was cleared, I'll update if it comes back tomorrow.

From what I can gather, this is an electrical issue. One forum asked the question of aftermarket accessories installed. I installed a stereo and amp 3 years ago and a light bar over a year ago, no issues until now. No additional modifications beyond LED headlights.

Anything I should look at for diagnostics?

[forester2002s]

Make sure that your AAA membership is up-to-date, so that you can get a tow if you get stranded.

These more modern designs, using CAN-Bus, are akin to fly-by-wire.  They can play-up at any-time, and are a nightmare to debug.

Sorry, but I can't be of more help.

[Daskuppler]

5 hours ago, forester2002s said:

Make sure that your AAA membership is up-to-date, so that you can get a tow if you get stranded.

These more modern designs, using CAN-Bus, are akin to fly-by-wire.  They can play-up at any-time, and are a nightmare to debug.

Sorry, but I can't be of more help.

No worries, thanks for the advice!

[Daskuppler]

Code came back, but no CEL.  Freeze frame shows it tripped after 968 seconds at idle.

[GeneralDisorder]

CVT is junk, CANBUS is junk. 10 years old - time to trade up or trade back to something that's not a rolling plastic computer. Is your phone 10 years old? Is your TV 10 years old? Exactly.....

GD

[Daskuppler]

28 minutes ago, GeneralDisorder said:

CVT is junk, CANBUS is junk. 10 years old - time to trade up or trade back to something that's not a rolling plastic computer. Is your phone 10 years old? Is your TV 10 years old? Exactly.....

GD

I know your opinion of these vehicles. I don't disagree... getting rid of it for a 30k piece of junk is not in the cards.

Where do you start troubleshooting? Is there a chance it can be fixed? Can it be replaced outside of a dealership?

[GeneralDisorder]

U codes are network errors. This almost always comes down to a wiring or module fault. All you can do is hook up an advanced scan tool and follow the clues. If there are no clues the only choice is to clean every ground, check every connection, and if it still comes back you start disconnecting modules while monitoring the network (in cases where a module is actually crashing, or corrupting it) or replacing modules (at great expense for parts and programming since used one's cant be VIN coded) in the order of most to least suspect based on the opinions and experiences of the dealer technicians that have seen these problems in the past. But at the end of the day it's a LOT of guessing. And if you aren't educated guessing it will take 10x as long. So factor that into your cost analysis of if you want to tackle it yourself or not.

I have plenty of vehicles with computers but I stick with vehicles that don't have networks of them. Discreet modules only that only share data by analog signaling or raw sensor data. The automotive CANBUS networks are very poorly engineered in terms of redundancy and error detection - in fact they basically have neither and you are left to swap parts randomly and guess at every turn because not only is there no error detection to point you to a cause, but all the network data is considered proprietary intellectual property.  

GD

[Daskuppler]

29 minutes ago, GeneralDisorder said:

U codes are network errors. This almost always comes down to a wiring or module fault. All you can do is hook up an advanced scan tool and follow the clues. If there are no clues the only choice is to clean every ground, check every connection, and if it still comes back you start disconnecting modules while monitoring the network (in cases where a module is actually crashing, or corrupting it) or replacing modules (at great expense for parts and programming since used one's cant be VIN coded) in the order of most to least suspect based on the opinions and experiences of the dealer technicians that have seen these problems in the past. But at the end of the day it's a LOT of guessing. And if you aren't educated guessing it will take 10x as long. So factor that into your cost analysis of if you want to tackle it yourself or not.

I have plenty of vehicles with computers but I stick with vehicles that don't have networks of them. Discreet modules only that only share data by analog signaling or raw sensor data. The automotive CANBUS networks are very poorly engineered in terms of redundancy and error detection - in fact they basically have neither and you are left to swap parts randomly and guess at every turn because not only is there no error detection to point you to a cause, but all the network data is considered proprietary intellectual property.  

GD

I take it Path A is a useless price of information? Are all of the modules in the CANBUS, or are only some systems?

[GeneralDisorder]

You would have to consult the network diagram but virtually all "modules" are on the network. Some things that are modules are not obvious - like the entire gauge cluster - that's a module. Everything down to the electronic parking brake has a module. The more advanced diagnostic tools have moved to an interface that shows network "topology" so you can see all the modules laid out sort of in their network diagram. The Thinkcar tools are popular for this:

As for "A" - no it likely won't point to anything unless it's a very advanced vehicle that has more than one network. Not likely in this case. 

Edited October 6, 2023 by GeneralDisorder

[1 Lucky Texan]

In the past, I've had spurious codes set, often with no driveability problems, on 2 different vehicles - that came down to weak/old/damaged batteries.

[Daskuppler]

56 minutes ago, 1 Lucky Texan said:

In the past, I've had spurious codes set, often with no driveability problems, on 2 different vehicles - that came down to weak/old/damaged batteries.

I'll check the battery, thank you. It's 5-6 years old but is an Optima Yellow Top.

 

Does the flashing cruise control light mean anything? Other threads seem to have different lights but the same code. Seems to be a lot with ABS and other brake lights, but still no actual problems.

Edited October 8, 2023 by Daskuppler

[Daskuppler]

Voltage was at 12.85.volts after a 10 minute drive. With engine off and accessories in(stereo, high beams, blower, and light bar, voltage was 11.91 and dropping .01 volts every 2-3 seconds. This doesn't seem that bad, should it be replaced?

 

Battery charger said it was at 75% charge.

[GeneralDisorder]

Flashing cruise is a result of the check engine light. Cruise control is automatically disabled as a driver alert for all system faults. It's to annoy you into getting it fixed.

Battery seems fine although Optima went straight into the toilet when they sent production to Mexico so I wouldn't recommend buying any of their products. Not that any of the battery manufacturers make really excellent consumer batteries anymore. Most are crap now. AAA stats show batteries are only lasting 2-3 years now due to quality and heavier electrical load on modern cars. 

[Daskuppler]

15 minutes ago, GeneralDisorder said:

Flashing cruise is a result of the check engine light. Cruise control is automatically disabled as a driver alert for all system faults. It's to annoy you into getting it fixed.

Battery seems fine although Optima went straight into the toilet when they sent production to Mexico so I wouldn't recommend buying any of their products. Not that any of the battery manufacturers make really excellent consumer batteries anymore. Most are crap now. AAA stats show batteries are only lasting 2-3 years now due to quality and heavier electrical load on modern cars. 

Okay, that makes sense. Although annoying. I've heard Optima. Went to spoob, but it was better than store brand crap for almost the same price that wasn't even a sealed battery.

[moosens]

“

CVT is junk, CANBUS is junk. 10 years old - time to trade up or trade back to something that's not a rolling plastic computer. Is your phone 10 years old? Is your TV 10 years old? Exactly.....”

GD

 

Rick, I want to thank for first for the assistance you offer when you somehow manage to spare time for the nice folks here, but also for putting out there straight for folks. I’ve saved this quote of yours to clue in folks I know driving these newer Subarus. 
 

We do have a 2006 and as I know it that’s fly by wire and that’s where guys like me turn yellow. 

My cars: 79, 94, 2003, 2003, 2006

 

Cheers! 

Edited October 9, 2023 by moosens

[GeneralDisorder]

The early DBW (drive by wire) isn't so bad in and of itself - the throttle body's have actually proven to be quite reliable (sadly not the pedal assembly however). It wasn't till about 2008 that most models went completely sideways with CANBUS networks. Do see plenty of the 05-07's with bad computers though. For that matter I see older Subaru's with bad computers though - just getting past 2004 you have to worry about programming them with VIN numbers if they require inspection and that's not always possible. 

Generally everything I see on the road now I just absolutely cringe at. In the last 10 years it's not even so much the complexity and the repairability - now they are a MAJOR privacy concern. The car industry is just absolutely a wreckage when it comes to privacy concerns. It's literally the wild west and your data is the stagecoach full of railroad payroll. 

Read:

https://foundation.mozilla.org/en/privacynotincluded/articles/its-official-cars-are-the-worst-product-category-we-have-ever-reviewed-for-privacy/

Edited October 9, 2023 by GeneralDisorder

[GeneralDisorder]

In other news it won't be long before I retire out of the Subaru (and consumer vehicle) repair world. I'm going to move to retired military hardware. Both the CUCV (square body chevy truck military platform), and the FMTV's like my M1079. Stuff you can actually repair and that was built to be durable and to keep your privacy intact. 

Maybe head up to the northeast and do some snow plowing with M1083's with sanders and plows. I've had a lifetime's worth of plastic consumer trash and I'm going back to my roots and my first love - OD green, desert sand tan, and 3-color NATO. 

GD

Edited October 9, 2023 by GeneralDisorder

[lmdew]

A loss for Portland, OR Subaru Owners for sure!  Enjoy the next phase of life.

Thanks for all the answers and information you provided on USMB!

[Daskuppler]

9 hours ago, GeneralDisorder said:

The early DBW (drive by wire) isn't so bad in and of itself - the throttle body's have actually proven to be quite reliable (sadly not the pedal assembly however). It wasn't till about 2008 that most models went completely sideways with CANBUS networks. Do see plenty of the 05-07's with bad computers though. For that matter I see older Subaru's with bad computers though - just getting past 2004 you have to worry about programming them with VIN numbers if they require inspection and that's not always possible. 

Generally everything I see on the road now I just absolutely cringe at. In the last 10 years it's not even so much the complexity and the repairability - now they are a MAJOR privacy concern. The car industry is just absolutely a wreckage when it comes to privacy concerns. It's literally the wild west and your data is the stagecoach full of railroad payroll. 

Read:

https://foundation.mozilla.org/en/privacynotincluded/articles/its-official-cars-are-the-worst-product-category-we-have-ever-reviewed-for-privacy/

Great article! The issues go far beyond where I thought they stopped! I would assume if you could remove the infotainment system and replace with an aftermarket, you would be fine... but most aren't removable anymore.

[GeneralDisorder]

12 hours ago, Daskuppler said:

Great article! The issues go far beyond where I thought they stopped! I would assume if you could remove the infotainment system and replace with an aftermarket, you would be fine... but most aren't removable anymore.

Nope. That's a CANBUS module also. Most cars think you are stealing the stereo and won't even attempt to start. 

GD

[moosens]

Northern NY for snow plowing. 
 

It’s the last nice quiet place that hasn’t been ruined or tainted by New Yorkers here in the northeast. I know that reads funny - think Yogi Berra.
 

Sorry to divert. Enjoy ! 

[Daskuppler]

Update: after disconnecting the driver's heated seat, the code has not come back after several drive cycles.

The bottom heater element has been broken for about a year, maybe it finally degraded to a point where it was causing interference. 🤞

[moosens]

Pardon my guesswork and general ignorance on this matter , but are these cars in any way similar to the old school where there were/are relays under the carpet/seat along the inner sill ? 
 

I know those old schoolers we’d have corroded connections and failures deluxe. 

[Daskuppler]

54 minutes ago, moosens said:

Pardon my guesswork and general ignorance on this matter , but are these cars in any way similar to the old school where there were/are relays under the carpet/seat along the inner sill ? 
 

I know those old schoolers we’d have corroded connections and failures deluxe. 

I faintly recall seeing some relays in there when I ran the amp wire, but I can't say for sure. There's been very little little moisture in the car and we live in a dry climate, but anything is possible!

[Daskuppler]

Update again: short story... GD was right as usual.

Long story:car was good for about 400. Miles, no codes, no problems. Sitting at a stoplight the dash light up like a Christmas tree. All systems turned off, transmission temp flashes, car went into limp mode. Drove it home cooked the code reader up and had two codes. U0073 and u0100 (loss of communication with ECM/TCM). Only engine and transmission codes where available, no other modules were listed or available to scan. U100 was listed as a transmission code, U0073 was on the engine.