E92 M3 won't ignition-on if OBDLink MX+ is active on PTCAN

DtotheL

Hey folks,

I'm trying to get data from my BMW E92 M3's PTCAN into Racechrono on iOS, using an OBDLink MX+. I've previously successfully used the MX+ to get OBD data into Racechrono, but now I want the additional data which isn't on OBD and is only available on CAN (steering angle, brake pressure, ABS active flag, etc).

I've tapped into PTCAN at the junction box (X14271 and X14272 connectors), and wired that to a J1962 connector, into which the OBDLink MX+ is plugged. The pins I've connected are as follows:

J1962/OBD pin 16 to X14272 pin 37 (switched 12V)
J1962/OBD pin 4 to X14272 pin 45 (ground)
J1962/OBD pin 6 to X14271 pin 1 (PTCAN high)
J1962/OBD pin 14 to X14271 pin 2 (PTCAN low)

If I try to power on the car, I get an exclamation mark on the cluster, and the car won't ignition on.

The MX+ is getting power and the ground is connected, shown by the LEDs coming on.

If I unplug the 12V or ground pin (i.e. power off the MX+), then the car is happy, and will ignition-on and fire up.

I measure 60 ohms across CAN high and low, both when the MX+ is plugged in (powered off), and when it's unplugged.

I'm interpreting all of that to mean that the CANbus is electrically healthy (i.e. the MX+ is not causing resistance changes), but the MX+ is probably sending frames on the bus which is causing issues.

I've looked for a way to switch the MX+ into a passive, listening-and-relaying-only device in the OBDLink iOS app but can't see anything.

Would others agree with my diagnosis? Has anyone made this work on an E9x already? Does anyone have any tips?!

Thanks!
David

aol

My 2009 E91 worked perfectly with my MX+. All default settings. I no longer have the car, but I believe it's not general incompatibility between the car and the reader. It could be some fault.