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Discussion Starter #1 (Edited)
Howdy.

2008 fortwo cabrio with 49k miles and a fresh battery that was just tested.

Worked fine all day...then suddenly...no PRND on dash display. Also won't start or switch out of P. Yellow button trick allows it to go to RND but still won't start and locks up again once put back into P.

Doesn't turn over or even try to start. It is as if it can't see its transmission.

Swapped clutch actuator... no difference. Checked main fuse...load tested battery...no change. Edit: I plugged in my relatively simple/cheap OBD reader and it showed no faults.

What would make the PRND disappear?

Thanks, -Eff
63789
 

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Discussion Starter #3
I can't believe I forgot to say this: I plugged in my relatively simple/cheap OBD reader and it showed no faults.
 

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Rather than try and DIY this, my recommendation is find a local shop that does Mercedes work and has a Mercedes STAR machine and let them check out the car. It may cost a little more but they can pinpoint the problem and save you money in the long run. Just my .02. :)
 

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Discussion Starter #7
Rather than try and DIY this, my recommendation is find a local shop that does Mercedes work and has a Mercedes STAR machine and let them check out the car. It may cost a little more but they can pinpoint the problem and save you money in the long run. Just my .02. :)
Thanks. That is a good point. I am new to all this and didn't realize folks other than M-B had those. Makes sense.

Might search a few more things (disconnected connectors?) before towing to a shop. But sold advice.

Probably time I grabbed one of these as well. For the future.
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I have another version of that, it's a good scanner for Mercedes cars. Just occurred to me, have you tried the transmission "teach-in" procedure? No guarantee it will do anything, but it's free....
Teaching-in the transmission system:
X Stop the vehicle in a safe location.
X Move the gear selector lever to park
position P.
X Turn off the engine.
X Wait at least 30 seconds before
restarting.
X Press the brake pedal.
X Restart the engine
Three bars instead of P appear in the
multifunction display.
X Wait at least 30 seconds.
The transmission is taught in.
When teaching-in was successful: P
appears in the multifunction display again
and normal transmission operating is
restored :)

Ignore all that - I see the car won't start.....
 

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Any recommendations for a better reader?

Thanks.
I have heard that the Torque phone app works with ELM and other inexpensive basic bluetooth/wireless scanners and can read canbus; I have not verified this though.
I have an iCarsoft MB v2.0 which works OK, though if I had to do it all over I'd toss more money at it and get a full fledged bi-directional scanner which I can use on more cars.

For the money, the iCarsoft seems to work fine (for me and for what I've needed to do with it)
Depending on where you are there's a chance someone nearby may have one and be willing to assist.

Edit: I believe the MB v2.0 supercedes the MB II.
 

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I have another version of that, it's a good scanner for Mercedes cars. Just occurred to me, have you tried the transmission "teach-in" procedure? No guarantee it will do anything, but it's free....
Teaching-in the transmission system:
X Stop the vehicle in a safe location.
X Move the gear selector lever to park
position P.
X Turn off the engine.
X Wait at least 30 seconds before
restarting.
X Press the brake pedal.
X Restart the engine
Three bars instead of P appear in the
multifunction display.
X Wait at least 30 seconds.
The transmission is taught in.
When teaching-in was successful: P
appears in the multifunction display again
and normal transmission operating is
restored :)

Ignore all that - I see the car won't start.....
I had the PRND disappear on me a few times a couple of years ago. My forever remedy was the good ol' tranny retraining routine. Probably ran the routine 10 times that night, and a few more times the next day lol. It worked. (psst! I also sprayed some lithium grease into the shifter motor omg... don't tell anyone)...
 

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Discussion Starter #12
I had the PRND disappear on me a few times a couple of years ago. My forever remedy was the good ol' tranny retraining routine. Probably ran the routine 10 times that night, and a few more times the next day lol. It worked. (psst! I also sprayed some lithium grease into the shifter motor omg... don't tell anyone)...
My car won't start. Was your car running when you did this?

Thanks.
 

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E, yes, it was running. I noticed that yours wasn't. Umm, could it be that your starter died at the same time your car couldn't see the PRND? It would be a huge coincidence, though.
 

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Discussion Starter #14
E, yes, it was running. I noticed that yours wasn't. Umm, could it be that your starter died at the same time your car couldn't see the PRND? It would be a huge coincidence, though.
I'm assuming the car can't see its transmission and accordingly won't start.
 

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Just a thought. There must be a sensor that detects where the shifter is. If it does not recognize the current position, it won't display anything. If the car doesn't think the shifter is in P, then it won't let it start. It the car is not started, then you can't move the shift lever. Maybe the detection mechanism some how got out of alignment or broke. Does the console where the shifter is located light up any of the P/R/N/D positions?
 

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The transmission control module is under the carpet under the drivers seat. Disconnect your battery and remove the key from the switch. Unplug the 3 connectors under the driver seat. Remove all 4 seat bolts and then fold up the seat and remove. Don't reconnect the battery or turn on the ignition switch with the seat connectors unplugged or you will trip your SRS (airbag) light. Clean the connector on the module. It is in a good space to get wet if the carpet ever got rained or spilled on. Either the connections are dirty or the module itself is bad. You can find used modules on ebay or Autobahn recyclers online. DCO
 

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Discussion Starter #19
Thank you. If I end up swapping it out, do I need to get the car to the dealership to reset/reflash it? Thanks!!!
 

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I'm no can bus master, but I have studied it some. It's a basic serial connection where multiple devices connect and share the media so when one device has issues or if there's a wiring problem it can throw codes in somewhat unrelated systems.

What I did was recorded all my codes, cleared them and kept rechecking for new codes (didn't take long!) until I had enough codes to see that some repeated all the time and others would come and go. Those that come and go are likely not directly involved.
 
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