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KBUS down

12477 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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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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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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