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no power to F5, no comm to TCM & BCM full of errors
Hi, my '05 Mini with CVT has been running great until... it began to not upshift; you know 20 mph at 3600rpm. Eventually got the "EP" limp mode. When I finally connected the scan tool (Creator C420) it showed:
P1611 - Serial Communication Link EGS/TCM
P1786 - Transmission Ratio Control Actuator
in the ECM2/DME2 module. Also, I have like 32 errors in the BCM/ZKE Body Control Module yet everything it controls functions normally - locks, lights, windows, etc. Pulled & inspected the BCM and it looks pristine; no water damage. All engine bay fuses test good. Left footwell fuses all good except for F5 which has no power. "F5 - Instrument Cluster Control Unit / Diode Communication Line" although my instruments work fine.
and still no TCM communication. According to page 4 here the TCM communicates via the CAN bus and there's only 5 modules on it. Therefore I disconnected each of the the other 4 modules individually; still no TCM found. I disconnected & tested the ECU/DME for resistance across CAN hi & CAN lo and got 120.2 ohms; therefore ECU seems good. Then found schematic for the TCM (page 136) and tested for power at pins 24 & 25 of the TCM X19561 connector and got 12.35 volts; good, the TCM has power. Interestingly, the 12v remains even after shutdown and removing the key.
So, am I correct in assuming either 1) CAN bus wiring issue, or 2) both TCMs are bad...?
As I understand, the TCM module doesn't have terminating resistor, just the 2 ends of the CAN network - in this case the ECU and the Instrument Cluster (speedometer). Anyway I measured the CAN lines (pin 15 & 16) and got 37.78 kOhms on the TCM itself (2004 module not installed) and then 1.83 M ohms on car's CAN network. I believe the car network resistance should measure 60 ohms. Thanks for the reply! Seems like I'm getting closer.
Ah, I believe you’re right about the terminations. Sorry about that. I normally work with a rather different kind of transmission line. Presumably the other modules are high impedance like the TCM you measured.
Yes, If the IKE and the DME are the terminations, then you’d expect to see the two 120 ohm resistors in parallel when measuring from any other node’s connector. Measuring from the IKE or DME’s connectors, you should see straight 120 ohms.
Last edited by deepgrey; Apr 24, 2025 at 01:28 PM.
Hang on... you're supposed to check with network asleep or battery disconnected. So I rechecked and got 60.3 ohms which is accurate for two 120 ohm resistors in parallel. This means CAN lines to TCM are good, and CAN lines to ECU and IKE/speedometer are good.
So now that my CAN bus lines test good to three modules ECU, TCM, and IKE - I'm wondering if my little code reader just isn't capable of reading the TCM? Or... maybe I've been driving it for years with no connection to TCM and now something serious has happened to the CVT (like stepper motor) preventing it from going into higher gears? I just reset the ECU and drove it to gas station and back (at 20 mph) and I have no "EP" mode and no ECU fault codes.
I'm going with the latter theory - that it's been running w no TCM communication - and will try replacing CVT valve body (with stepper motor). Will report back.
Could there also be something up with the D-bus preventing the code reader from talking to the TCM? Sorry, haven’t had much time to think about this, and I’ve also never owned anything that didn’t have a manual transmission.
Yes Deepgrey, that is possible. One of the diagrams showed a power steering module on the diagnostic bus but not sure if this Mini has that module. Anyway, I got it back together today and ...
it seems no better. Tried to do the CVT adaptation but it won't go into xP mode. Will try again tomorrow.
