W210 1999 E300-weird transmission issue
 

My friends car is having a weird issue with the trans. It has just recently (within the last 2,000 miles or so) had a complete trans service with a new filter, drain and refill with synthetic fluid. It has worked fine until a few days ago when the weather got cold at night. He went to work a couple days ago, and being cold, the trans would not shift out of first. It eventually did, and then at the next stop, it started out in the gear it eventually shifted to (probably 3rd or 4th). Once the car/trans warmed up, it shifted perfectly. This morning he started the car and put it in drive with the parking brake on a half hour before leaving for work (I told him that was a bad idea!), and I he trans shifted perfectly again. I can only imagine it being a sticking solenoid, being an electronically shifted transmission, but can't be sure since I am not a trans expert. I do and can handle most everything engine related on this car (recently did a head gasket job from leaking coolant), but transmissions, other than basic mantainance are above my pay grade. Anyone have any ideas?

Check the electrical connector the o ring tends to fail allowing ATF to wick up the wires and eventually reach the ECU.

The conductor plates also are a problem and may need a new one. Solenoids can be removed and tested with the conductor plate off.

If you or anyone you know has a high grade scanner or SDS, you can run the transmission through diagnostics and it'll tell you everything you need to know. I have an HHT, Xentry, and an Autel DS708 around that can do that for me. The Autel does everything the Merc stuff does, plus being able to check every other car known to man.

If the trans isn't slipping when warmed up and we're just pissing in the wind - trans conductor plate failing. If the car hasn't set off any limp codes yet, you can get away with replacing the plate and not needing a high grade scanner to delete any TCM failures. While the work is being done for that, a new connector plug/seal should be put in.

which fluid dId they put in it?

He needs to pull trans trouble codes and clear them / drive until a fault then pull codes again before going any farther, don't guess. Also have a look at the ABS system as wheel speed info comes from that system.

Idling in gear for 1/2 Hr won't cause any damage as long as the parking brake holds.

The initial shift might have been the car going into limp ( this trans defaults to 2nd gear ). If it actually made it into a higher gear, the trans will stay in that gear until the engine is shut off. ( This is to prevent the trans from hitting limp / 2nd if there is an electrical issue while at speed. )

It is common for the case connector bushing to allow fluid to wick up the wiring to the trans computer, this can cause issues due to the fluid being slightly conductive. ( Graphite / metal dust in the fluid ) Cleaning the trans computer is possible. Mounting the trans computer connector down helps keep fluid out as it will continue to wick even after the case connector is sealed up.

All of that being said, diagnose and don't change parts at random.

Thanks all for the replies. Although the diagnosis procedures and repair sound like DIY, I still need to educate myself in those procedures. I have no idea what a conductor plates are or where they are found, so again, more research is needed on my part. As for fluid, if I remember correctly, it was Valvoline full synthetic (red gallon bottle).
EDIT Yes it was Valvoline MaxLife which meets the standard.

Try overriding 1st using winter mode, it may eve be a problem with this switch as seldom used during summer.

Update
 

Just yesterday I put the car (it belongs to my friend Dave) up on the lift (in Dave's shop) and pulled the valve body out to replace the conductor plate and adapter. I ordered Genuine parts from Pelican. The job went very well. Even though there was only a couple thousand miles on the synthetic fluid, I opted to do a complete fluid change anyway (drained converter as well). I got it back together and drove it around the block, and it shifted great. Every Friday I have breakfast with Dave and a few other guys, and I asked him how the trans worked this morning. He said "don't ask". I assumed something was wrong, and he then told me it was doing the same thing as before. He was not happy that $500 was spent on the trans, and nothing has changed. It seems that only on very cold mornings the trans won't shift out of first until warmed up. If he parks the car in his garage, it works fine in the morning. What else could be causing this after the new conductor plate was installed? I would think the only thing left would be a solenoid, but which one? Although the job of removing the valve body should be easier next time, I would like to avoid it if I could. So here I/we are, back to the beginning.....Rich

He tried that, and it did not change anything.

There has not been one single trouble code yet.

This sounds like the classic battery voltage scenario.
There is enough power in battery to start the engine but in doing so other ecu's are robbed of power and in the case of the gearbox ecu protest by not working properly until either the car is switched off and on again or battery voltage rises to a suitable level.
Hence why it works once warm , oh and this will not give any codes to be read neither.

make your freind notice the gear select indicator on the dash when its cold - I have seen one E320 doing that and I had to change the little white selector switch in the shifter box to remedy this.

I found that when the shifter position was being seen intermittent.

This is also sometimes thrown by a weak battery

two tests
 

Dave parked the car in the garage the day before yesterday, and it worked perfectly the next morning. He parked it outside last night (45 degrees for the low), and it would not shift out of first until he parked it and let it warm up for 15 minutes. After that, the trans shifted fine. It sounds like a sticking solenoid, but I could be wrong. However, I don't want to pull the valve body again to replace a solenoid unless I am confident that will fix the problem. Dave is still not too happy having to spend so much money, and still have the same problem.......Rich

Wow, wished you guys were closer. I'd offer Dave some $$ to take this problematic, expensive E300 off his hands. I have a rebuild kit, valve body, conductor plate, torque converters, everything for this car. I don't mind owning these or the w124 diesels. I've got two w210s and one w124. I'd buy another of either.

Are you able to see live trans data? If so, look at requested gear , actual gear and shifter position.

If you are looking for codes in the engine computer, they won't be there , need to get into the trans computer with the 38 pin under hood connector ( at least on 1997 cars, however at some point in later years, everything went through the under dash OBD 2 )