SL/R129: Transmission fluid squeezing electrical harness into transmission control unit?
Thread Starter
Newbie
Joined: Aug 2012
Posts: 12
Likes: 0
1998 SL500
Transmission fluid squeezing electrical harness into transmission control unit?
I have a 1998 SL500 whose check engine light came up recently. I took it to my mechanic and he said it was a transmission code, and after inspecting the car, described a problem I hadn't heard before.
He said that the transmission control unit has gotten transmission fluid in it, and needs to be replaced. However, the really confusing thing is that the transmission control unit is ABOVE the transmission. So naturally, I wonder, how did the transmission fluid get up there?
He said that it's a problem he's seen before, where the transmission fluid is under such high pressure that it can actually squeeze through the insulation of the electrical harness and up into the transmission control unit. Obviously, this would also mean that the wiring harness is fluid-logged, and if I was to just replace the control unit, the problem would quickly reappear. He said that instead of spending multiple thousands to replace the electrical harness, he could clean out the harness and use solder dots to block the fluid from continuing to get into the transmission control unit.
I'm wondering, is this an accurate diagnosis? Is there really enough pressure on the electrical connector to squeeze transmission fluid through the electrical harness up into the control unit? Do I need to replace the transmission control unit? And will the harness cleaning operation be useful, or am I on the hook for a new electrical harness?
He said that the transmission control unit has gotten transmission fluid in it, and needs to be replaced. However, the really confusing thing is that the transmission control unit is ABOVE the transmission. So naturally, I wonder, how did the transmission fluid get up there?
He said that it's a problem he's seen before, where the transmission fluid is under such high pressure that it can actually squeeze through the insulation of the electrical harness and up into the transmission control unit. Obviously, this would also mean that the wiring harness is fluid-logged, and if I was to just replace the control unit, the problem would quickly reappear. He said that instead of spending multiple thousands to replace the electrical harness, he could clean out the harness and use solder dots to block the fluid from continuing to get into the transmission control unit.
I'm wondering, is this an accurate diagnosis? Is there really enough pressure on the electrical connector to squeeze transmission fluid through the electrical harness up into the control unit? Do I need to replace the transmission control unit? And will the harness cleaning operation be useful, or am I on the hook for a new electrical harness?
Senior Member
Joined: Aug 2006
Posts: 391
Likes: 6
From: So California
2000 SL500
I'm wondering, is this an accurate diagnosis? Is there really enough pressure on the electrical connector to squeeze transmission fluid through the electrical harness up into the control unit? Do I need to replace the transmission control unit? And will the harness cleaning operation be useful, or am I on the hook for a new electrical harness?
Member
Joined: Mar 2013
Posts: 90
Likes: 0
s320cdi /SL350/Slk 230
Hi Lynn's
You are so right. MB have been aware of this problem since about 1996. Yes, the oil can go
'Uphill' the wick principle. Remember the old oil lamps of bygone years where the paraffin travelled up the wick and whic was the lit to create the flame- same principle here - except of course it shouldn't be happening in an MB!!!
That plug adaptor you referred to is a bushing and as been coloured coded by MB so that they will know when the bushing was last replaced by reference to its colour. Such remedial work will not be mentioned to the client for fear that the serious nature of the problem can be conceled. You shouldn't have to ay MB for such a repair as they knw that it s a well know defect in the design and manufacture of the transmission. It can lead to serious problem for the driver because when theECU gets flooded with oil it doesn't know hot to cope and hence you can ave such problems as a title loss if power - otherwise car going into a false neutral or simply downshifting when you will least expect it. Effectively the car becomes a potential death trap. I have had a case against MB and won where m car suffered loss of power and almost caused our death. You have to be careful ad the problem hasn't been resolved and an happen again. The statistic given to me by my engineer is that one in every three MB with the 722 transmission has this defect.
Be careful
You are so right. MB have been aware of this problem since about 1996. Yes, the oil can go
'Uphill' the wick principle. Remember the old oil lamps of bygone years where the paraffin travelled up the wick and whic was the lit to create the flame- same principle here - except of course it shouldn't be happening in an MB!!!
That plug adaptor you referred to is a bushing and as been coloured coded by MB so that they will know when the bushing was last replaced by reference to its colour. Such remedial work will not be mentioned to the client for fear that the serious nature of the problem can be conceled. You shouldn't have to ay MB for such a repair as they knw that it s a well know defect in the design and manufacture of the transmission. It can lead to serious problem for the driver because when theECU gets flooded with oil it doesn't know hot to cope and hence you can ave such problems as a title loss if power - otherwise car going into a false neutral or simply downshifting when you will least expect it. Effectively the car becomes a potential death trap. I have had a case against MB and won where m car suffered loss of power and almost caused our death. You have to be careful ad the problem hasn't been resolved and an happen again. The statistic given to me by my engineer is that one in every three MB with the 722 transmission has this defect.
Be careful
