View Single Post
      04-23-2012, 04:14 PM   #164
Major General
doughboy's Avatar
United Kingdom

Drives: 2016 M6 Gran Coupe LCI
Join Date: Jan 2009
Location: UK - Midlands

iTrader: (2)

Originally Posted by simonsingh View Post
These little devices are able to work out which wire is which (as the OBD pin config changes from year to year/model to model), and then work according. Any swapping of the wires is just a waste of time.
CANBus relies on EITHER of the 2 communication wires, knocking one of them out will also do nothing for security.
The CANBus system is also very sensitive to any wire changes or breaks. Once the wire is broken and soldered, you're going to have endless problems as the solder itself changes the resistance of the part of the wire.
Anything do to with switches, or soldering CANBus wires is going to be bad news.
These hooky programming boxes do not / cannot figure out pinouts, maybe a CAN line reversal but that would be it, even so I doubt even that. There's no need as OBD pinouts are fixed!

1. OBDII pinout is strictly fixed has been since day 1, CAN is on pins 14&6 and that's it - that's the whole point - its a global standard access port for all cars!! What use would it be it if BMW changed the pinout?. There are allocated spare pins that manufacturers can uses as they wish but they are not the CAN / power etc and the four other protocols, which are fixed for all. Any 'spare' pins they do choose to use must not interfere with any other pins or any other diagnostic equipment.

2. CAN needs both high and low wires, it's a balanced pair network usng differential signalling between the wires so it has to have both wires intact at all times (and the polarity is critical too). It will not work on one wire where 2 are specified - other wise they would only provide one wire!

3. CAN is very robust (it's meant to be), as long as extensions are done in twisted pair wire (0.35 to 0.5sqmm ideal), keeping both H & L the same length, you can run up to 40 meters and still maintain full data speed. Neat in-line soldering is fine, or small diameter through crimps, taped up after finishing.

You only have to look at the JB4 connection to the ECU, using non-twisted wires and simple in-line connections, there is no problem to the CAN bus with this.

OBDII pinout (fixed since 2004) Five comms protocols are allowed for, but CAN is always on 14&6.


1 - Discretionary

2 - SAE-J1850 PWM and SAE 1850 VPW positive bus line

3 - Discretionary

4 - Chassis ground (battery negative)

5 - Signal ground (max 1.5 Amp)

6 - ISO-15765-4 CAN (high line) and SAE J2284

7 - K-line of ISO-9141-2 and ISO-14230-4 (data line)

8 - Discretionary

9 - Discretionary

10 - SAE-J1850 (PWM) (negative bus line) (not SAE 1850VPW)

11 – Discretionary

12 - Discretionary

13 - Discretionary

14 - ISO-15765-4 CAN (low line) and SAE J2284)

15 - L-line of ISO-9141-2 and ISO-14230-4

16 - Positive voltage (battery positive, max 4 amps)
E90 330i 6MT gone. E91 335i 6MT gone. AMG E63 Estate gone. M6GC current...

Last edited by doughboy; 04-24-2012 at 04:41 AM.