I picked up an 04 R50 with two issues (not starting and not shifting into higher gears with a CVT). Using ISTA and INPA, I found that the transmission would throw an EP error once it had issue with the Speed Sensor (0721). I attempted to replace the original, same issue arose immediately. I replaced the connector...same issue. Thought it might be a bad sensor...replaced with no fix. Noticed the wire on the pigtail had burned up the insulation was completely gone, exposing bare wire on all three wires. I replaced the engine wire harness and another sensor...burned up again! No issue on the wire in the harness, just from the connector to the sensor. I asked an electrician friend and he said it was possibly too much amperage or possibly bad ground? Any suggestions?

The car is started, moved no more than 100 yards, checked and the wire is already destroyed.

 

The insulation is burned bad on both ends and cracked on all three wires all the way through...this is true of all four sensors (original and replacements). Two wires to the computer and one to the engine fuse box...where do I begin to look? If I put another on, it will just burn it. I took the engine fuse box apart but did not see any burnt connections or corrosion. I suspect either the computer or fuse box, but I'm not sure where to go from here?

 

No ideas?

 

If the mechanic thinks to much amperage then replace the alternator to correct the regulator issue. No ideas other than that.

 

I didn't replace the alternator yet...but this is all that I have done. I may look into that next. Any other ideas?

Replaced engine computer, engine fuse block, engine wire harness, transmission control computer and of course a handful of sensors.

 

The stepper motor may be shorted out!

 

Thanks, I failed to mention I swapped out the trans valve body too... I'm stumped!

 

I hate reading through posts and not having any conclusions and resolutions! With the basketball season and moving, this project was put on hold until this weekend.

As Tgriffithjr pointed out...it was the alternator (diode in the voltage regulator)! Swapped the alternator this weekend and this MINI is running! After resetting ABS sensor lights and CVT adaptations, I was 65mph on the county roads!

I highly recommend INPA for watching the analog values (Engine 1 option) for watching the speedometer and output speed sensor readings as they should closely match. Previously, my output speed sensor was at 0 while my speed reading was accurate.

I found this video on youtube, Bad Alternator Diode causing transmission/speedometer problems, . It is a great watch regarding the similar issues I had!

Thanks Tgriffith for the assist!