Error code: U0079 Control Module Comm Bus G off

[Jonathan0880]

Really cold today, -35C overnight, -20 during the day. Truck started fine but had no power when I first got it going (felt like the safety systems were deregulating things). Check engine light eventually came on. After some warm up, everything seems fine. I don't understand the error codes. Just looking for a heads up on what it could be before I bring it to my mechanic.

ECU1 (FD00)
U0079 Control Module Communication Bus G off
ECU2 (FD20)
said same thing

[Gamb1t]

If the vehicle under your profile is correct, yours is a 2016 X1 which is based off the FWD Mini cute-ute. 'fraid you best post it over in the other forum.

This X1 forum here is based on the 3-series platform. Quite different. All the best!

[Jonathan0880]

just changed it, didn't notice it was wrong.. I have a 2013 X1 E84.
Also this issue is most likely my hot air blower, as it seems to have quit. I'll post back when I have a better diag from my mechanic.

*Update: As per my mechanic and his diag, looks like this was an air blower and water pump going bad. The codes above are probably not that good. I need to get a better diagnostic tool. I ordered a OBD2 dongle for
connecting via phone app. Should provide better diagnostics.

[8memphis8]

I just have the same code. I turned in the car to BMW for ECM programming recall, it still has the same issue. They want me to pay $185 for diagnostic. I know I need motor mounts, they told me so, and I felt the vibration as well. ALong with U0079, there are U0001, U0100, and 3B97. All pointed to Data Bus, No communication with PCM. Any suggestion?

[wheela]

Originally Posted by Jonathan0880

Really cold today, -35C overnight, -20 during the day. Truck started fine but had no power when I first got it going (felt like the safety systems were deregulating things). Check engine light eventually came on. After some warm up, everything seems fine. I don't understand the error codes. Just looking for a heads up on what it could be before I bring it to my mechanic.

ECU1 (FD00)
U0079 Control Module Communication Bus G off
ECU2 (FD20)
said same thing

Not sure about your codes, but even if nothing is wrong with your engine, it will feel less powerful when your engine is that cold. This is because for each combustion event, you'll lose alot more heat through the cylinder walls than you would when the engine is warm (bigger temp. delta = more heat transfer out of the cylinder). This means lower cylinder pressure for each combustion event for a given load (less heat available to do work). Gradually as your engine warms up, heat loss will decrease bringing cylinder pressure back up until you've got full power once your engine is fully up to temp. Plus the oil in the engine and transmission will be much more viscous at those temps, so you're also losing more power to friction.

I'm not saying that there isn't also something going on with your engine, just that it would feel less poweful in those conditions, regardless.

[Jonathan0880]

Just to follow up. I replaced the water pump and blower, parts were covered under my people's choice warranty. Water pumps aren't cheap. Seems like the codes that I read were just basic stuff. I'm not sure what the mechanic was getting with his scanner. He also mentioned my battery was defective. He said he got a code saying it wasn't taking a charge. That's a fresh battery only after one year. He told me to use my car more to keep it charged. I work from home so it sits for sometimes a week in the cold... anyway. recap of what I replaced so far.

Bought in 2019 with ~54,000km's. Almost 2 years of use now and 74,000km's...

- Battery, twice.
- Coils and plugs and motor cover (broke the vaccum tube)
- Thermostat
- Water pump
- HVAC Blower motor

I bought a high level third party warranty, it's about half paid for itself alread..

So far, not bad I guess... seems to be all the "issue" things that go wrong with this model.

[Jonathan0880]

Originally Posted by 8memphis8

I just have the same code. I turned in the car to BMW for ECM programming recall, it still has the same issue. They want me to pay $185 for diagnostic. I know I need motor mounts, they told me so, and I felt the vibration as well. ALong with U0079, there are U0001, U0100, and 3B97. All pointed to Data Bus, No communication with PCM. Any suggestion?

Really tough to say unless there's an actual issue that is noticed...also different diag tools will show different codes. I have a dinky one, it shows only the basics. FWIW, seems like U0079 is pretty generic and doesn't reveal much.
Try to find a trusted mechanic that specializes in bimmers and see what they say. BTW. 185$ seems a little high for a diag. My guy does it for ~100 and change.

[Jonathan0880]

Originally Posted by wheela

Not sure about your codes, but even if nothing is wrong with your engine, it will feel less powerful when your engine is that cold. This is because for each combustion event, you'll lose alot more heat through the cylinder walls than you would when the engine is warm (bigger temp. delta = more heat transfer out of the cylinder). This means lower cylinder pressure for each combustion event for a given load (less heat available to do work). Gradually as your engine warms up, heat loss will decrease bringing cylinder pressure back up until you've got full power once your engine is fully up to temp. Plus the oil in the engine and transmission will be much more viscous at those temps, so you're also losing more power to friction.

I'm not saying that there isn't also something going on with your engine, just that it would feel less poweful in those conditions, regardless.

I posted a follow up of what was wrong. Yes, I don't think the system de-regulated, it was actually just the cold, it was crazy cold that day. I noticed that it lacks power at first when it's particularly cold and get's better as it warms up. I lean towards the tranmission fluid being the main bottleneck with the xdrive units. You can feel the engine is trying to turn through thick mud...

[5mall5nail5]

Originally Posted by Jonathan0880

I posted a follow up of what was wrong. Yes, I don't think the system de-regulated, it was actually just the cold, it was crazy cold that day. I noticed that it lacks power at first when it's particularly cold and get's better as it warms up. I lean towards the tranmission fluid being the main bottleneck with the xdrive units. You can feel the engine is trying to turn through thick mud...

Sorry to bump - I took my wifes 2015 X1 in for inspection this AM, it was cold (25ish) overnight, and the CEL was on. I read the codes with a Foxwell NT510 and got U0079 generic OBD2, but went into the BMW interface and saw 3B97 and 3B99 pointing to water pump "missing". Watched a youtube video where dude says any LIN Bus is a broken wire - I don't fully believe that. What ultimately fixed your 3B97 issue?

Thanks!