All I can tell you is that in my case the bad module was the window that didn't work. I guess one way to test M.B. Doc's theory that "the rear module can effect the front module" is to unplug the rear module/motor. If the front still fails then I would suspect the front. The module is built into the motor, which is integral (although removable) from the regulator assembly. I got the whole thing from a junk yard for 60.00. And they guaranteed that it would work. And it does.

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

From what I can tell on EPC net, there is only one control unit in the 99 C230 for the passenger's side controls.....there is another one on the driver's side for those controls. Both appear to be in the front doors.

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1995 E300 Diesel
1994 E320
1999 C230K
1994 S500 W140
1990 300 SEL

Well the dealer sells it as a complete regulator with motor and integral can computer in the motor housing. So they probably just list it as "motor" or "regulator".

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

Actually not....the electrics in the door are seperate from the regulator...I wish there was a way to pull the picture from EPC net....it would explain allot.

The part number shows to be
A 210 820 76 26 - Control Unit Right

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1995 E300 Diesel
1994 E320
1999 C230K
1994 S500 W140
1990 300 SEL

Well the motor and control are all one piece and are removable from the regulator as I said. I did not know you could buy the motor separately though.

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

MBDOC is right, unplug one or both rear door motor/modules and the fault will clear. they fail and drag the CAN down causing issues with front door and overhead control panel modules plus are super expensive.

I'm trying to decide on second hand or new ones.

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Turbo 202 history:
http://www.cardomain.com/ride/735658

FWIW the used one I bought over 7 years ago is still working.

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

Just bought my wife a used '99 with same problem as OP. Indy mech says I need a driver's door module and wants crazy money for one. Is this what I need?

97 00 Mercedes W202 C220 C230 C280 Left Front Door Module Control 2088201326 | eBay

Is this right part number?

Thanks,
Scott

OK, I'm having this problem on my 2000 C230. The driver's window is inoperative. If I disconnect the battery, it will work for a day or two then won't work again. If I understand what's being said here, it may be a problem with a window other than the driver's side. Can I just pull the fuses for the other windows to see which one is causing the problem?