Code P0748 - Page 6 - Mercedes-Benz Forum
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#51 (permalink) Old 01-09-2009, 08:38 PM
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Originally Posted by pma View Post
Pin 29 is the power supply from the battery, the current passing thru the circuit via voltage regulator and out to pin 38 to supply current to the Modulating Pressure Valve (Y3/6Y1) or the Shift Pressure Solenoid Valve (Y3/6Y2) and (Y3/6Y1).
I did the same process replacing several solenoids and the culpit was the ECT.
Good call. My ETC arrived today and just like that I'm back on the road. I replaced it and all is well in the world again. Thanks to you and Witek for all your help.

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Last edited by JaxML; 01-10-2009 at 03:28 AM. Reason: Typo
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#52 (permalink) Old 08-16-2010, 05:53 PM
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where exactly is the ETC located so i can take it out and be done with this please
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#53 (permalink) Old 08-16-2010, 07:50 PM
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where exactly is the ETC located so i can take it out and be done with this please
Right side of driver's footwell.
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#54 (permalink) Old 01-13-2011, 05:36 PM
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awesome post!

R/R my conductor plate, e-plug (13-pin connector ATF leak), and found my ATF crept up to the ETC module connectors. I cleaned both ends of the wire harness w/ electrical cleaner then cleared the ECU and ETC fault codes. Transmission was still shifting funny so I performed the testing procedure here (w/out a battery charger hooked up to my battery) and came up with these results:

1) 30/29=10.35V
2) 30/1=0V (Diagnosis Output)
3) 30/38=9.67V

Looks like my ETC is Kaput as well. Seeing about getting a re-manufactured unit that can be encoded to my VIN right now...

Thank you all for this very informative post! Thanks Witek!...and everyone!
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#55 (permalink) Old 05-30-2013, 08:57 AM
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i'm new to using a voltmeter so please excuse my ignorance

i'm guessing the proper method of testing pin 38 is to have the harness with pin 30 plugged in? i'm assuming i should plug in the power side and then leave the pin 38 side unplugged so i can touch the positive terminal on my voltmeter to it?

is there a pin i should use to connect my negative terminal to? or just any grounded surface in general should work?

i don't see any other way of testing this since the harness is in the way

-blacked out 02 CL500 to 02 CL55 ///AMG engine/tranny swap, coilover suspension, Lorinser fenders and trunk lip, 2 12" kicker CVR's, 20 inch Giovanna kilis in flat black

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#56 (permalink) Old 05-30-2013, 09:37 AM
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okay so once i figured out that pin 30 and pin 1 must be tested simultaneously i decided to instead probe the harness itself (with key in on position) and got no sign of electrical current (negative probe in the 30 pin slot and positive probe in 1 pin slot as shown on one of the diagrams already posted)

kinda lost, am i doing something wrong? or did i just successfully diagnose my TCU as faulty? i don't understand how testing the wiring harness could conclude the TCU itself being faulty so i'm not sure what i did was correct

-blacked out 02 CL500 to 02 CL55 ///AMG engine/tranny swap, coilover suspension, Lorinser fenders and trunk lip, 2 12" kicker CVR's, 20 inch Giovanna kilis in flat black

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#57 (permalink) Old 05-30-2013, 01:31 PM
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okay i figured out the wiring harnesses can be disabled so you can back probe the pins while the harness is plugged into the tcu...no power from 30 - 1 so i'm assuming it's time for a new tcu (etc)

tested from 30 -38 but only got around 3-4 volts... perhaps this is because my etc needs replaced? or do i have problems elsewhere

-blacked out 02 CL500 to 02 CL55 ///AMG engine/tranny swap, coilover suspension, Lorinser fenders and trunk lip, 2 12" kicker CVR's, 20 inch Giovanna kilis in flat black

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Last edited by ctravis595; 05-30-2013 at 02:46 PM.
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#58 (permalink) Old 05-30-2013, 07:29 PM
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What exactly is the MB Star Diagnosis saying when trying to communicate with the ETC?

If it has not been checked with a an MB Star system you will just be throwing parts at it. If you do replace the ETC it will still need the MB Star system to do it right.
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#59 (permalink) Old 05-30-2013, 09:02 PM
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i'm not entirely sure. i recently had the old fault codes erased (p0715), after reinstalling another transmission, filter/fluid change and replacing 13 pin connector. after it ran great all day then the car wouldn't move from a redlight. found out battery terminals weren't making a good connection. cycled the ignition and then found myself stuck in limp mode. tranny read out code p0748 at this point

considering i highly doubt my solenoids are bad, it seems the ETC is the only logical culprit. the wiring harness voltage test concludes this. (pin 30 to pin 1, no voltage = bad wiring or bad ETC according to WIS PDF shown earlier in the thread). i thought perhaps it was a bad voltage spike from the battery terminals not being properly connected, and tightening the battery terminals and doing a tranny code clear would fix the issue. took the car to a local mercedes specialist that says they can clear all the codes that the dealership can and they say after clearing the p0748 code comes right back

-blacked out 02 CL500 to 02 CL55 ///AMG engine/tranny swap, coilover suspension, Lorinser fenders and trunk lip, 2 12" kicker CVR's, 20 inch Giovanna kilis in flat black

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#60 (permalink) Old 05-31-2013, 12:45 AM
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You haven't even said what your problem is. You simply chose this tread and decided to start testing.

What is your problem and what code/s are you getting?
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