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W124 300ce-24/M104980/722.5/1993
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12 Posts
Discussion Starter #1
Gentlemen,

Some time ago, on W124 subforum I've posted question about what can be reason of strange behaviour of my tranny, and I've received information, that since my configuration is pretty rare for W124, I should look for help here. Orginal question was
I am "lucky" owner of the gearbox 722.5, where fifth gear is controlled by the module HGS. The problem is that the fifth gear works selectively. Sometimes it works - that times fourth gear is ommited in sequence, but often does not work.
I made a diagnosis of electrical system according to checklist from WIS but without these points requiring the measurement to be done on running car. One of the points of the checklist refers to "digital load signal" where the vacuum is connected to the ignition system, multimeter connected to pins 1 and 13 of HGS slot, should indicate a voltage of 0.8V, while the absence of vacuum should show above 2V. In my case indication is equal to 12+V, and rapid throttle response instantaneous drop to about 10V. Originally I thought that the element that converts an electrical signal depression in the ignition system is suspended or is short, but since it seems to be responding to throttle, it's probably the reason lies elsewhere.
In addition, the problem is that trying to "blink-out" error code from the diagnostic socket (pin 13) does not return any value. Generally, the LED is lit all the time no matter whether I press the reset button for 3 or for 13 seconds.
Sometimes it is so that the LED is connected to this jack for significant time stays off then after while it becomes lit, and sometimes it is so that lights up immediately after the key is positioned to ignition.
Have any of you met with such behavior HGS driver? Can guess what I have done before I will give serious money on a visit to an authorized service center?
Unfortunately, I do not know anybody with another car in this configuration and I can not replace my unit with another HGS which would know that it works correctly.
I've waited some time in meanwhile doing some electrical research, then I've bought another - used part - HGS (5th gear controler) module and yesterday I've installed it. But behaviour of module/transmission is the same - Fifth gear is not working when on diagnose socket 13 I receive constant light instead of blinking.
Could anyone here have idea what can be reason of such behaviour? I am loosing hope, that I can manage some time to clear this issue out.
 

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Registered
W124 300ce-24/M104980/722.5/1993
Joined
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12 Posts
Discussion Starter #2
Time for update.
Yesterday I've exchanged speedometer and other gauges cluster, and it seems, that there was reason of problem with my gearbox. Probably speed signal wasn't returning to HGS module. Now it works perfectly, react on gear selector and kick-down.
 
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