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P1786 Code/ Car in EP mode?

Tiny
BRIAN STEWART
  • MEMBER
  • 2008 MINI COOPER
  • 1.6L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 138,000 MILES
I recently took my vehicle listed above convertible to an import mechanic shop and they used a diagnostic code reader that gave the code P1786/ Transmission Ratio Plausibility. I was told, "There's an internal excessive ratio error, we will need to replace the transmission." I need help understanding what that means and if it means there is no choice but to replace the transmission. They want to charge $7,000 to replace it.
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Sunday, January 21st, 2024 AT 1:21 PM

1 Reply

Tiny
BORIS K
  • MECHANIC
  • 795 POSTS
Hello,

Your vehicle is fitted with the 6-speed automatic Aisin TF60SN transmission.

P1786 - ratio plausibility

This fault code could have several different causes.
The basic fault means that the engine speed and transmission speed, actual/desired, are outside of specific parameters.
This could be caused a gear slipping inside the transmission, an issue inside the valve body (hydraulic controller inside the transmission) or possible speed sensor issues external of the transmission.

See a video regarding valve body issues:
https://youtu.be/b_rDACqbsDw?si=W09Yh4Y2KmCfVV4h#
and
https://youtu.be/s5CNDQZmKlg?si=TGA2fLZuUif8hxt8

I would suggest getting a second opinion.
Perhaps try:
https://www.transmissionsolympia.com/mini-cooper-tf60sn-transmission-repair/

They appear to specialize in transmission repair for your vehicle.

Cheers, Boris
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Monday, January 22nd, 2024 AT 4:03 AM

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