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G55 2004 WONT SHIFT INTO HIGH

11K views 9 replies 6 participants last post by  schnuelle 
#1 ·
My 2004 AMG G55 is not shifting into high. There were no signs up front. It just started to shift up to 3rd and stays there. Has anyone ran into this issue?
 
#4 ·
My money would be on the conductor plate also, but I would also inspect the connector where with wiring harness connects to the transmission for fluid leaks first. The O-rings harden over time and the leak, causing loss of transmission fluid and potentially causing problems with the electrical connections at the plug. Either of these can put the transmission into limp-home mode or cause intermittent shifting problems. Replacing the plastic part with the O-rings is easy and cheap.

If you discover fluid around the connector, I would also check (or have checked) the transmission fluid level. It's not easy on the 722.6 because MB seals the dipstick tube with a little plastic hymen that says "MB workshop only" and they do not provide an actual dipstick, but you can buy one easily at a number of places.

I also have an 2000 SL500 (R129) with the same 722.6 transmission and have had shifting problems related to the o-ring seals on the connector twice in 68K miles.

- FD
 
#9 ·
My money would be on the conductor plate also, but I would also inspect the connector where with wiring harness connects to the transmission for fluid leaks first. The O-rings harden over time and the leak, causing loss of transmission fluid and potentially causing problems with the electrical connections at the plug. Either of these can put the transmission into limp-home mode or cause intermittent shifting problems. Replacing the plastic part with the O-rings is easy and cheap.

- FD
This is a very well known problem. MB has updated the connector several times in an attempt to fix the problem. In addition to leaking out of the connector, it can also wick fluid up the cable and into the ECU. This is an expensive fix, if it happens.
 
#5 ·
I had the same symptom on my 2002 G500 around 100K mi a few months ago, suddenly went into limp mode for the first time ever.
My MB master tech looked into it.
It turned out to be a sensor, here is the conclusion post I did on the other forum at that time.

"Code is P2206. It specifically identifies the external output speed sensor. We have no indication of an issue with the internal speed sensors [Ed: aka conductor plate mentioned in prior posts]. My mechanic says that they already have seen the issue with the external speed sensor a number of times. Also my transmission shifts wonderfully smoothly, partly because of the frequent oil/filter changes I have had done."

So the recommendation would be to pull the exact codes your G shows.
 
#6 ·
A bit more technical information on the similar case I had.
(post is "transmission output speed sensor" from August 2014 on the other forum)

Shortly after the limp mode, the trans was perfect again.
2 codes showed up, pointing to:
- B49 transmission output speed sensor (mounts externally to the rear of the transmission). I understand the G is the only Mercedes vehicle to require that additional speed sensor for the 5-speed transmission. If the trans does not get a speed signal, it stops shifting. Very easy to replace though.
- N36 transmission output speed sensor ballast (located in the rear under the CD changer). This is the relay that controls the sensor, has a long cable that routes through the car and takes more labor to replace.

Apparently, at least one of them at some point the day that the trans went into limp mode was "bad" and caused the transmission to stop shifting. Don't know which one. We ended up replacing both, the relay was more expensive than the sensor because of the labor.
 
#8 ·
Just Google "722.6 dipstick" - eBay, Amazon, etc., they are not hard to find.

One additional point I would like to mention . . From your initial post, I assume you do not have a Check Engine Light or you would have mentioned it. I managed to trigger a CEL for the rear transmission speed sensor on my G while running it on a lift (part of my long vibration saga). This immediately triggered a CEL (which I reset with a code reader), but neither of the two incidents with my SL caused a CEL despite the shifting problems. If you have a CEL, get the codes read. If not, check the connector seal and fluid level.

Edit: One more thing, if you do check the dipstick, use it to check the fluid level, but do not leave it in place. You must remove it and replace the cap on the dipstick tube after you have checked the fluid level.
 
#10 ·
I checked for leaks and nothing near the tranny as described. I have not checked tranny fluid level yet. I need the dip stick still. So this is the wife's car. When this issue started she called me and said the check engine light did come on. She drove it back and and parked it. A few days later I took it out to test drive. There is no check engine light on or malfunctions showing on the control panal. Now, here is the kicker. On the panel I see the L above the PRND is lit up. I have done the manual shift and it will shift from 1 to drive and it shows this as I shift. Yet I can not go more than 30mph running 3000 rpm.. I assume the wife may have pressed a switch to put in LOW but i cant figure it out. Has anyone had this issue or experience that may be able to help. Thank you. Chad
 
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