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KBUS down

12512 Views 9 Replies 6 Participants Last post by  Bucko521
Problem.....Electrical problems started last year after washing the car: intermittent, loss of radio controls, roof up/down, signal light ticker. Stored over winter and found battery dead (7 yrs old and replaced with a BMW original). Electrical problems got worse: radio went disabled, roof and windows would not go up or down and signal light ticker did not work, some loss of KOMBI info display. Otherwise the car ran fine. Took to dealer thinking a factory reset was required. Dealer could not connect to the OBD or KOMBI...the KBUS was down. Drove home with the intention of diagnosing KBUS over the summer. Electrical problems got worse: car would not start after driving across an international bridge into the USA.

The Cause: BMW IPOD interface connection at wiring harness connection shorted out and took the entire KBUS down. Removed IPOD Interface and KBUS and all functions restored.

Troubleshooting Method:
1) Purchased BMW TIS/EKT and WDS CD for $30 off EBAY...essential
2) Searched Forums and YouTube for possible causes and troubleshooting methods.
3) Sketched out a matrix of modules/connections and wire numbers to manage the acronyms and the troubleshoot starting with the most logical modules....CVM, Radio, LZM given the early electrical problems.
4) Imagined the KBUS/D BUS and PT CAN BUS loops from battery to module and back laid out on my kitchen table.
5) Used TIS and WDS and ETK to locate KBUS modules and started to "expose modules and connectors"
6) plan to use OBD Fault reader to monitor KBUS readability and voltage at pin 14 of KOMBI wire harness connector: should be greater than 7VDC...from forum members and the WDS I learned that a problem module if disconnected should restore the KBUS.

Troubleshooting...took base line readings at battery VDC, AMPS, checked all fuses and OBD reader: "could not" and conducted the "car reset": disconnect battery touch leads together wait 5mins, 2 hrs etc....then
1) followed safety warnings in TIS. WDS concerning battery amps and airbag pyros.
2) removed trim panels to expose 90% of KBUS modules, gnd hubs and wire harness connectors. (Bagged and labelled everything for ease of reassembly)
3) checked all fuses with multimeter in the cockpit and under the hood.
4) connected OBD reader and started to remove one module at a time. Removed EWS, LSZ, CVM, SZM, EKPS, IHKA, GM, RAdio, AMP, SZM and KOMBI....I did not touch PT CAN Engine Modules
5) I saw no no change at OBD reader: looking for a "car to OBD Reader connection"
6) checked for KBUS voltage at pin 14 of KOMBI. Voltage was 0 VDC.
7) Checked Pin 21 at KOMBI (Data BUS) and got 3.5 VDC.
8) Checked Pin 17 at KOMBI (PT CAN BUS) and got 0 VDC.
9) Checked 90% of gnd hubs and connections for voltage; should find 0 VDC and found 0 VDC.
10) Checked amp draw at battery as I plugged one module in at a time. Sleep mode draw should be around 20 to 30mA. Amps jumped to 645mA when the radio was reconnected.
11) concluded that problem was with modules, gnds or connectors that I was not willing to remove trim to get at.
12) prepared a summary and towed car to dealer and conferenced called with the mechanic.
13)dealer concluded it was the KOMBI that had to ship from Germany although I could have got one from a dealer in South Atlanta for half the price. The test would be at no cost to me so I agreed. The mechanic and I talked again and I reminded him about the specific connections from the WDS that needed to be looked at.
14) when the KOMBI replacement did not work he removed trim and opened up the harness at one location where those connections are and discovered the open circuit: BMW IPOD interface connection was bad. I do not know if this was factory or dealer or an owner installed IPOD, I bought the car used.

Hope this helps others...the threads I read sure helped me.

It is ridiculous that an entertainment component can take a car down.
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Nice job of sticking with this to the fix! This is an unfortunate vulnerability in many modern digital electronics systems (not limited to just your car). To reduce the number of wires in the harnesses, two wire com busses are used where one device on the bus is a master and the other devices are slaves. (Note: There are systems with ordinal masters but the vulnerability is the same). Each has a unique digital address so that communications can be managed without bus conflicts. It's an efficient system when it works, but if one device suffers a failure where it doesn't release the com bus then all communications on that bus are dead. Troubleshooting now devolves to disconnecting one device at a time until communications are restored to ID the faulty device. Some techs have had enough training to understand this, but some are just relying on connecting the diagnostics computer and having it tell them what the fault is. With a dead comm bus this obviously is a dead end for the latter.
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Z4 (E85) KBUS Followup

Thanks DC our cars are identical including the rims...

I thought that I should clarify a few points for others..

1) the car wash: my electrical issues were coincidental with the car wash and since Z4 convertible top motors are prone to flooding and burnout it did cross my mind as the cause. A technician can supposedly verify a burn out by attaching a 12VDC power supply to the motor power supply leads located behind the CVM before going through the effort of removing the roof. We did not do this.
2) the bridge crossing: the bridge is a one mile drive across a bridge deck made of steel grating. The vibration was enough to shake the bad connection loose and when I next shut the car off no more ignition: the engine would crank but not fire. I had fuel flow, lights and numerous other electrics but no firing. At the time I thought it might have been the immobilizer. But given the loss of data flow on the KBUS to the KOMBI the PT CAN was not getting the information and permissive s required for PT CAN modules to function.
3) The BMW Virtual PC DVD (for all models)is worth the $20. It takes time to learn to navigate through all the information, it helps when you enter your VIN Number (enter last two letters and 5 numbers of your VIN) and it filters out all other models. I tried to piece information together from the internet like too many folks asking the same questions and looking for info that they can get from this simple buy....

TIS: how to locate repair and disassemble everything including module locations
WDS: wiring diagrams, component and connector locations with visuals
ETK software: BMW Parts catalogue shows exploded views of parts including such things as wiring harnesses and routing through the car, and the drain assembly in the roof motor well, part prices.
PDF's electrical troubleshooting guides for all models up to 2004

EBay Seller: mvkmimi1
Cost $20
Title: BMW WDS - Electrical Wiring Diagrams & Schematics + TIS & ETK- Repair Manual DVD
I run it on my HP Laptop using windows 7 (it comes with a version of Windows XP which loads when you run the application)

4) in the Z4 the KBUS main connections are located in the wiring harness behind the glove box near the fuse panel. BMW engineers should be able to engineer a KBUS health indicator based on voltage...and place LED fault lights on the fuse panel. The technician who fixed my car opened the harness, located the connectors and opened them all (4): he had voltage on all but one line, he traced that and found the bad IPOD connection. Unfortunately the connection was made in a convenient but poor location in the circuit that stopped voltage flow to the KOMBI and took the whole system down. There are many similar forum topics like this: after market speakers, radios installs and shorts etc.
5) My car does not have a CD changer, NAV system ...but I did find wiring and connectors already factory installed for those options, behind trim.
6) Trim removal. I made my own plastic trim removal tools from stiff hard plastic kitchen utensils I bought at the dollar store...little bit of cutting and edge filing....or talk nice to your local dealer and borrow a set.
7) Search by Z4 or E85...there is lot more out there under E85 than Z4, there is also a lot on the net when you enter proper E85 acronyms such as CVM, LSZ etc

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Bshackle, thanks for taking the time to post your problem and resolution. Looked like a long and frustrating process to find a relatively simple fault (but at least not an expensive fix). I'm curious, did you end up reconnecting the iPod interface somewhere else? You only mention disconnecting the iPod interface to restore functionality to the rest of the systems.
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enzed4, we did not reconnect the BMW IPOD interface. The technician followed a std shop protocol: they repeated what I did rather than investigate the 10% I could not get at. Cost two tows and $1500 of shop labour, I had stripped the car down and put it back together otherwise it would have been more. The good thing is that this dealer shop had never seen a complete KBUS down and had to consult with the fatherland after the std troubleshoot prescribed by the DIS failed. The IPOD connection was not on any wiring diagram and was not pre wired with a BMW plug in connector at the factory. So at some point someone made a poor connection at a bad location. The car from the factory is very well put together and comes apart fairly easy. The software I bought for $20 tells you how to do it. Even so I was not willing to take out air bag pyrotechnics to get at some of these connectors and left that up to a qualified shop.
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not shocking it took the car out I had my park distance module get wet, it disabled the car. First the dash went out then the car would no longer run I guess it floods the network with bad data and disables communication on it
Unfortunately I understand why the shop had to repeat everything you'd already done, frustrating as it was for you (reading your fault finding processes it looks like you know what you're doing). I am an engineer (Telecoms) and I do a lot of fault work. If I listened to every customer who swore they had tested something and that definitely wasn't the fault, only to find (after hours wasted looking elsewhere) that they hadn't tested correctly, or at all, I would not get a lot of faults fixed. Plus your mechanics probably couldn't go to next-level support until they had followed a checklist of troubleshooting themselves, so even if they believed you had done everything right, they still had to follow their 'script'. I'm just sorry that it cost you $1500 to see someone else duplicate what you'd already done.
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I respected what the technician did and appreciated the process he ran. I designed, built, operated and maintained chemical plants for 30yrs, wrote functional and technical logic for process control systems. The contractors, consultants, engineers and electricians I worked with followed troubleshooting processes that were very logical and therefore predictable. I was always surprised by what I learned about people and processes when things went wrong. One key direction I gave to teams I led was "trust but verify". I learned what I had to about the car so I could trust the shop process and verify the fix. We share a similar background so we are less likely to get surprised when and if we have to take the car to the dealer.
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It seems strange they would have installed the OEM iPOD interface at the wrong location as it comes with detailed instructions. It should only be connected at the back of the radio. I didn't think you could order the car with it installed from the factory either. Glad you resolved it.
Just went through a VERY similar thing. Car was basically having much the same issues (although mine was running). In the end, it was a faulty GapTech roof module causing the situation. Cost me nearly $1000 to 'diagnose' the issue. de-installed the module and everything worked 100%. The BMW Stealership wanted to replace the main KBUS and everything connected. That would have cost me a fortune.

I really need to get my own WinXP laptop and install the software to do some of the diagnostic work myself.
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