CEL U0073 Causes

[GeneralDisorder]

2 hours ago, Daskuppler said:

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.

Woof. That's rough since either the ECM or the TCM could be at fault and the car won't operate without them so you can't just disconnect them and see if that stops the codes. At that point I would start with disconnecting and cleaning both of their connectors (Deoxit is a good choice for connector cleaning) and see if the issue returns. Followed by probably replacing the TCM since that doesn't require programming (I don't think anyway), and if that doesn't do it..... might have to replace the ECM but that requires programming the immobilizer, keys, and VIN, etc. 

Could still be grounding issues also - clean every connection you can find. Also these low voltage coms can be disrupted by outside influences - bad alterntors, aftermarket stereo and accessories, etc. Remove all aftermarket wiring and return the vehicle to 110% stock if it's not already.  

The ECM's seem to be getting less reliable for Subaru's. We had one that seemingly got smoked when the customer smashed his COBB Access Port cable in the door - we ordered a replacement and after programming it worked but continuously threw a code for one of the intake runner control valve actuators - after troubleshooting it down to the ECM itself we bought a second brand new unit and that solved the problem - so #1 (maybe) killed by a short on the OBD-II port, #2 bad out the box from the dealer (returned as faulty).

GD

Edited October 14, 2023 by GeneralDisorder

[Daskuppler]

14 minutes ago, GeneralDisorder said:

Woof. That's rough since either the ECM or the TCM could be at fault and the car won't operate without them so you can't just disconnect them and see if that stops the codes. At that point I would start with disconnecting and cleaning both of their connectors (Deoxit is a good choice for connector cleaning) and see if the issue returns. Followed by probably replacing the TCM since that doesn't require programming (I don't think anyway), and if that doesn't do it..... might have to replace the ECM but that requires programming the immobilizer, keys, and VIN, etc. 

Could still be grounding issues also - clean every connection you can find. Also these low voltage coms can be disrupted by outside influences - bad alterntors, aftermarket stereo and accessories, etc. Remove all aftermarket wiring and return the vehicle to 110% stock if it's not already.  

The ECM's seem to be getting less reliable for Subaru's. We had one that seemingly got smoked when the customer smashed his COBB Access Port cable in the door - we ordered a replacement and after programming it worked but continuously threw a code for one of the intake runner control valve actuators - after troubleshooting it down to the ECM itself we bought a second brand new unit and that solved the problem - so #1 (maybe) killed by a short on the OBD-II port, #2 bad out the box from the dealer (returned as faulty).

GD

I don't think we're going to tackle this one, we have an international trip in two weeks. We'll see what the dealership says. Where are these control modules located? The ECM looks like it's about 1k and the TCM looks to be about $600...

[Daskuppler]

The stealership said there were no hard codes everything was fine so they can't do anything. The CEL was on and the cruise control light was flashing when it went on the tow truck...

Is there anyway to troubleshoot it with an intermittent issue and no hard codes?

[heartless]

On 10/13/2023 at 10:42 PM, Daskuppler said:

I don't think we're going to tackle this one, we have an international trip in two weeks. We'll see what the dealership says. Where are these control modules located? The ECM looks like it's about 1k and the TCM looks to be about $600...

i am curious about ownership - how long have you owned the car?

did you buy it new, or used?

If used, any idea where it came from?
 

[Daskuppler]

2 hours ago, heartless said:

i am curious about ownership - how long have you owned the car?

did you buy it new, or used?

If used, any idea where it came from?
 

We bought it with 20k miles on it in May of 2017. 141k on it now.  The car was originally sold in Washington, but came from the Midwest before it was traded in at a dealership in Colorado. I don't know how much time it spent in each locale.  The car is still relatively rust free apart from the usual suspension parts. It has had its own spot in a garage since we purchased it.

[GeneralDisorder]

On 10/18/2023 at 2:16 PM, Daskuppler said:

The stealership said there were no hard codes everything was fine so they can't do anything. The CEL was on and the cruise control light was flashing when it went on the tow truck...

Is there anyway to troubleshoot it with an intermittent issue and no hard codes?

No. No practical way and worse than that - no one at the dealership that is A: Skilled enough to do it, and B: Willing. You see every technician at the dealer level is paid "flat rate" - so they get paid book time. And when you can do a 2.8 hour spark plug job in 1 hour and get paid for 2.8 hours..... or you can troubleshoot some random CAN code that at best is going to take MANY hours and you will get paid probably for fewer hours than you actually spend.... which are you going to choose? They are going to scan it - write "unable to reproduce customer complaint" on the invoice, get paid their 0.5 for the scan tool diag and move the heck on to an actual paying job.

They don't have the skills and the dealer isn't going to pay them for the research necessary to acquire those skills for one problem child car. It's not economically viable. 

Now you are beginning to understand.....

Could a team of engineers with a laboratory equipped with a dyno that can angle and shake the vehicle while it is simultaneously driving under various ambient conditions and is hooked up to CAN sniffer equipment, and all 4 channels of half a dozen oscilloscopes find the problem? Given enough time..... YES! Is that likely to be funded by you or anyone else? No - as a society we will just throw that car away and build another. 

This is how it's basically always worked with technically complex manufactured products. Hell my LMTV (US Army truck) had an electrical fault that took ME eight months to find. Because it was intermittent and the troubleshooting documents and the engineers that designed that particular system (yes I spoke with them - multiple times) did not foresee this particular interaction of failures and so the symptoms could not be correlated with the actual problem. I eventually found it by pure force of will and by resorting to testing every single wire end-to-end for every component involved in the subsystem exhibiting the problem. I found a manufacturing defect in the truck's wiring harness by application of brute force, time, and a lot of luck. And that truck has no CANBUS in the sense that none of it's modules talk to each other. The US government spent $230,000 to purchase that truck in 2008. They sent it to Kuwait and then shipped it back to El-Paso. From 2008 to 2017 the truck accrued 2,045 miles of use, and was then deemed "surplus to needs" and (probably) because of the electrical fault and some minor damage (not related to the electrical and easily repaired with only bolt-on replacements) it was not selected to be upgraded to full armor so was sent to auction. This is the DOD - with a budget of $860 billion. It was deemed not economically viable due to a single wire not having been soldered correctly at the factory that "in practice" no one could actually isolate. So the whole truck was sent to the corn field. 

Sadly - unless you want to become an expert in CANBUS networks and sniff out the problem yourself - at the cost of great expenditure of time and effort - Subaru could care less if they lose you forever as a customer. It's a statistics thing. A convert will come along that had a bad experience with a Ford to replace you. It really isn't to anyone's financial benefit except you to spend the effort to find the problem because in the end it will require so many hours to do so that it will far eclipse the value of the car and you won't pay for that so no technician is going to spend the time. 

It's a bit of a societal problem in general but the ever-increasing complexity, the drive for ever-increasing profit by creating the artificial need to replace products frequently, and the ability to release products while they are still in a software beta state and "online" update them later if and when there's enough complaints is really reaching an intolerable level. At least for me. Basically everything we buy is now total garbage and we have forgotten the two most important of the three R's. Everyone thinks it's all fine as long as it's "Recycled". No one bothers one bit with Reduce or Reuse. Just throw it "away" (where the hell is that exactly?) and get another one. Someone will recycle it.... probably into a landfill or into your lungs via a convenient incinerator.  

GD

Edited October 20, 2023 by GeneralDisorder

[Daskuppler]

6 hours ago, GeneralDisorder said:

No. No practical way and worse than that - no one at the dealership that is A: Skilled enough to do it, and B: Willing. You see every technician at the dealer level is paid "flat rate" - so they get paid book time. And when you can do a 2.8 hour spark plug job in 1 hour and get paid for 2.8 hours..... or you can troubleshoot some random CAN code that at best is going to take MANY hours and you will get paid probably for fewer hours than you actually spend.... which are you going to choose? They are going to scan it - write "unable to reproduce customer complaint" on the invoice, get paid their 0.5 for the scan tool diag and move the heck on to an actual paying job.

They don't have the skills and the dealer isn't going to pay them for the research necessary to acquire those skills for one problem child car. It's not economically viable. 

Now you are beginning to understand.....

Could a team of engineers with a laboratory equipped with a dyno that can angle and shake the vehicle while it is simultaneously driving under various ambient conditions and is hooked up to CAN sniffer equipment, and all 4 channels of half a dozen oscilloscopes find the problem? Given enough time..... YES! Is that likely to be funded by you or anyone else? No - as a society we will just throw that car away and build another. 

This is how it's basically always worked with technically complex manufactured products. Hell my LMTV (US Army truck) had an electrical fault that took ME eight months to find. Because it was intermittent and the troubleshooting documents and the engineers that designed that particular system (yes I spoke with them - multiple times) did not foresee this particular interaction of failures and so the symptoms could not be correlated with the actual problem. I eventually found it by pure force of will and by resorting to testing every single wire end-to-end for every component involved in the subsystem exhibiting the problem. I found a manufacturing defect in the truck's wiring harness by application of brute force, time, and a lot of luck. And that truck has no CANBUS in the sense that none of it's modules talk to each other. The US government spent $230,000 to purchase that truck in 2008. They sent it to Kuwait and then shipped it back to El-Paso. From 2008 to 2017 the truck accrued 2,045 miles of use, and was then deemed "surplus to needs" and (probably) because of the electrical fault and some minor damage (not related to the electrical and easily repaired with only bolt-on replacements) it was not selected to be upgraded to full armor so was sent to auction. This is the DOD - with a budget of $860 billion. It was deemed not economically viable due to a single wire not having been soldered correctly at the factory that "in practice" no one could actually isolate. So the whole truck was sent to the corn field. 

Sadly - unless you want to become an expert in CANBUS networks and sniff out the problem yourself - at the cost of great expenditure of time and effort - Subaru could care less if they lose you forever as a customer. It's a statistics thing. A convert will come along that had a bad experience with a Ford to replace you. It really isn't to anyone's financial benefit except you to spend the effort to find the problem because in the end it will require so many hours to do so that it will far eclipse the value of the car and you won't pay for that so no technician is going to spend the time. 

It's a bit of a societal problem in general but the ever-increasing complexity, the drive for ever-increasing profit by creating the artificial need to replace products frequently, and the ability to release products while they are still in a software beta state and "online" update them later if and when there's enough complaints is really reaching an intolerable level. At least for me. Basically everything we buy is now total garbage and we have forgotten the two most important of the three R's. Everyone thinks it's all fine as long as it's "Recycled". No one bothers one bit with Reduce or Reuse. Just throw it "away" (where the hell is that exactly?) and get another one. Someone will recycle it.... probably into a landfill or into your lungs via a convenient incinerator.  

GD

I agree with pretty much all of that. We live in a throw away society and pretty much everything is crap.

My assumption is that all of this equipment is inside the car behind panels and is connected with that single 2 conductor braided wire. It seems like it's highly unlikely the wire went bad being inside the car where things are relatively protected. That leaves the modules I presume there's no real way to figure out where the break in communication is based. On the fact that only certain modules were reachable? I'm assuming that the communication is fairly linear since a bus system requires the signal to pass through one module to the next. It seems like, if you were willing to throw some. Money at it, that you could assume if communication dropped off after, say the TCM, eeither the TCM is bad, or the module immediately following it. I obviously. Don't understand how all of it is setup though.

[GeneralDisorder]

No it's not a linear connection like that. It's completely parallel where everything on the network communicates simultaneously (kind of like the internet). Messages are being sent and received constantly and there's a multi-level system of priority, arbitration, error detection, and CRC checking that's all part of the message protocol to ensure messages don't collide with each other and that messages are received by the intended target(s). The problem arises in that the data inside the messages (which module the messages belong to and are intended for, and their payload) is proprietary intellectual property and without that information you can't decode the signaling. The network can be sniffed and all this reverse engineered but to reverse engineer just one module's message data can be hundreds of hours of labor. It can and is done in the performance aftermarket - for example we have a 2021 STI running on a LINK standalone and because it's an "enthusiast" vehicle there have been efforts by the manufactures of aftermarket ECU controllers, etc to decode the CANBUS data so their products can interface with the vehicle. But it's literally something you pay a CANBUS engineer ~$10,000 to decode for your product. 

GD

[Daskuppler]

We finally got it back from the dealership where they told us they drove it all over the place trying to get the code to come back...they drove a whole 8 miles, but I digress.

I got some contact cleaner and pulled the connections off the ECU, cleaned everything up and put it back together.  Everything looked fine, except the top connection in the ECU won't snap and lock in. It looks like it should, but won't. I tried using some channel locks to gently push it together and it would slide an extra 1/16th" but went right back to where it was as soon as I let go and would never lock.  Could this be the root of the problem? The connector looks like it's together all the way.

The car runs fine now, time will tell.

From what I read, the TCU should have beenounted right below the ECU but I didn't see anything else there, does anyone know where I might be able to find it to clean the connections there as well?

[Daskuppler]

Update: after cleaning the connectors in the engine bay, we drove the vehicle about 1000 miles without issue. This morning, at idle and neutral (shifting from park to drive) a bunch of codes came back along with some new ones.  Restarting the car cleared everything except the fuel sensor code.  Wiggling the previously mentioned plug did nothing. The car was driveable but sluggish and hesitant to shift.

General Codes:

U0101 Stored: lost communication with TCM

U0101 Pensing: lost communication with TCM

U0100 Pending: Lost communication with ECM/PCM "A"

U0101 Permanent: lost communication with TCM

ABS/VDC Module:

C1431 Current: AT Abnormal

U0100 Current: CAN-HS ECM No-receive Data

TCM Codes:

U0100 Current: Lost communication with ECM/PCM"A"

Engine Codes:

P0462 Current: Fuel level sensor circuit-low input

U0101 Current: Lost communication with TCM

Meter Codes:

U0073 History: Control Module Bus "A" off

U0151 History: Lost communication with restraints control module

U0100 History: lost communication with ECM/PCM"A"

Multi Function Display Codes:

U1201 History: H-CAN Error Counter Fail

U1201Current: H-CAN Error Counter Fail

Electric Power Steering Codes:

C2543 Current: Error passive status

Body Integrated Module Codes:

U0100 History: lost communication with ECM/PCM"A"

U0100 Current: lost communication with ECM/PCM"A"

Here is a link to the freeze frame data, it is the same for all of the codes:

 

[Daskuppler]

Diagnosis and solution can be found here: