Friend of mine's 99 ML320 is throwing an error code 700, Transmission Control fault. What could be wrong with the tranny?

Any DIY thingies I can do? The stealership wants $1700 just to do a test. Also there is NO transmission dip stick, how can one check the fluid level and quality of fluid, color/burnt smell etc?

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

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1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

Many independent shops can read transmission codes that will help with diagnosis.
That should be the starting point.

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