LH Module cross Test and Repair - Capacitor replacement

[mikachantw]

ADMIN UPDATE: Additional information on replacement caps at this post. Also, forum member @Alphasud offers a capacitor replacement service, click here for details.

First, I have to say this forum is very good that I didn't seen before.
Everyone share know-how and help each other. Some information I got from here and help me a lot.
Today, share some information about my LH module repair and cross test with W140 M119 93' LH module.

My car is 1992 EURO 500E with early LH module but got some idle trouble before. (ex: cold start is not easy and after car warm then get idle problem. like misfire.)
Therefore, I got one early LH module from my friend and installed it then everything works fine.

Repair LH module

Sometimes you get LH idle issue it might related to the capacitance of LH.
There are 6 major capacitance (Color in Brown) in LH module as below.

3 x Large = 100uf/40V
3 x Small = 22uf/40V



but those capacitance are hard to purchase, therefore, I used the
100uf / 50V
22uf / 50V
for those.

Try hard to remove those original capacitance and install new one.

After repair those capacitance, my LH module is back.
If you have idle problem and check if it's LH module issue. you can try this for repair.

Cross Test

I also got LH module from W140 m119 93'. It's the late LH module can be installed in early 500E.
I have checked information from this forum. Later LH module w/o WOT.
Open the module for compare the early LH module as below.

1992 500E



1993 S500




After I checked the electronic component, it's almost the same!? only the PCB is different.

The early module, the PCB with cement for protect the hot issue and link of two PCB is easy to damage.

The later module, the PCB w/o cement for protect and link of two PCB more stronger than early one.

Drive information

I drove my 500E with the W140 LH module around 5 days. Just feel smooth than my original module...
Try to replace the 28 pin EPROM from W140 (2 287 357 922) to my original 500E (2 287 357 428) ...
OOOP~ after I installed the 500E EPROM, it was not smooth but ran like the early LH module. I don't know why....

If you can get the 28 pin EPROM from 1992 500E and try install into the later LH module.
It will be different than you drive before.


Just share those information to you. sorry my poor ENG.

 

[Alphasud40]

I wanted to add to this post since I am offering a LH capacitor update for forum members. So far in my observations the only LH that has the bad capacitors are the 92 models. It’s pretty easy to remove the LH from the module box and remove the circuit boards from the case using a T15 and a T10 screwdriver. If your caps are brown they need to be replaced sooner than later. The metal can caps all have been checking within tolerance so replacing them will just give you the piece of mind they won’t fail in the future.

Here is a illustration of what tools are needed. Flush cut cutter, T10 and 15 screwdrivers, a vacuum solder removal tool or solder wick, a small toothbrush to clean the rosen from the board after soldering, a good solder iron 20-30 watt with a fine tip, and good solder. I use the 60/40 rosin core solder that was used when the module was produced. The industry uses lead free solder which tends to be more brittle.




Here are a couple pictures of the original capacitors. Note the negative leads all face in the same direction and their values are printed on the top. Unfortunately QC has made marks over some of the values so in the next picture take note of the orientation of the 22 and 100uf caps.



You will see the upper capacitor is 100uf and the bottom caps alternate 100,22,100,22



In the previous post he mentioned the EPROM chip under this cover. This is the software written for this module. If you have a 92 WOT LH that has failed. This EPROM can be removed from its socket and be installed in another LH Module to retain the WOT feature.



You can see this is mounted in a socket and can be gently levered out. Take note of the notch on the end of the microchip and make sure you don’t reinstall backwards.



Just testing one of the old capacitors. These component testers came on the market a few years back. They can identify most active and passive components and it’s a cheap and quick way to test. I have some expensive test equipment and this is remarkably accurate.


As far as changing the components if you have never soldered I recommend you get a inexpensive kit to build before you tackle this job. The removal method I use is I heat the solder joint while gently rocking the capacitor to free it. Then I alternate back and forth until the leads are free. Then I clean my iron tip and apply fresh solder to the tip and heat the hole while simultaneously drawing the solder from the hole with the pump. Then it’s just the matter of installing the new component and soldering the leads. Then remove the rosin with alcohol and a clean rag after giving it a scrub.

 

[Jlaa]

Thanks @Alphasud40 !

 

[Jlaa]

I just wanted to point out that @Alphasud40 does superb work - high quality, quick turnaround, and exceptional communication.
He's clearly an experienced electronics technician!
He did my 1993 LH for me and is now off to do my 1992 LH with capacitors that I supplied.

 

[Jim Rosenthal]

Another tip of the hat to Alphasud40- he repaired my 1992 LH module and my 500E runs great now.

 

[mutleybird]

I wanted to add to this post since I am offering a LH capacitor update for forum members. Then it’s just the matter of installing the new component and soldering the leads. Then remove the rosin with alcohol and a clean rag after giving it a scrub.

Hi,
I saw your post about LH module capacitors. Does your replacement offer extend to the 1993 M104 W140 LH module?

I had to change the wiring harness, (it wouldn't run when I bought it) and it starts up fine, and had crazy idle fluctuation (hunting).
After disconnecting the maf, it smoothed down with no miss when starting from cold - but after a while it went into a less severe hunting mode of 1100 -1250 rpm, - then smoothed out somehow when I put it in reverse, then back to park.

But, it never settles down to a normal 700 or so, RPM.

Thanks,
- Larry

 

[Alphasud40]

Hi,
I saw your post about LH module capacitors. Does your replacement offer extend to the 1993 M104 W140 LH module?

I had to change the wiring harness, (it wouldn't run when I bought it) and it starts up fine, and had crazy idle fluctuation (hunting).
After disconnecting the maf, it smoothed down with no miss when starting from cold - but after a while it went into a less severe hunting mode of 1100 -1250 rpm, - then smoothed out somehow when I put it in reverse, then back to park.

But, it never settles down to a normal 700 or so, RPM.

Thanks,
- Larry

I can certainly look at the module for you but to the best of my knowledge the HFM module didn’t suffer from bad capacitors. If you haven’t pulled codes in the modules that would be your next step. If the car hasn’t run in a long time there could also be other factors like old fuel or incorrect fuel pressure causing issues. The module could have been damaged from a shorted harness. I could look it over for burnt drivers.

 

[gsxr]

I saw your post about LH module capacitors. Does your replacement offer extend to the 1993 M104 W140 LH module?

The 1-year-only LH-SFI module for M104/140 should have the same/similar capacitor arrangement as the M119 modules. I think.

I had to change the wiring harness, (it wouldn't run when I bought it) and it starts up fine, and had crazy idle fluctuation (hunting).
After disconnecting the maf, it smoothed down with no miss when starting from cold - but after a while it went into a less severe hunting mode of 1100 -1250 rpm, - then smoothed out somehow when I put it in reverse, then back to park.

But, it never settles down to a normal 700 or so, RPM.

Have you checked fault codes with a blinker box yet? Could have an issue with throttle control, the T/LLR module on non-ASR cars, or E-GAS for models with optional ASR. These modules control idle speed.

 

[Wosserlock]

Hi,

I would like to ask about the issue with the capacitors. Do they only cause the clicking of the fuel relay, or could they also be responsible for the fuel relay (fuel pump) not working for 3 seconds when the ignition is turned on?

Let me explain: My 500e has the problem of the clicking fuel relay. Additionally, when I try to start the car after it has been parked for half a day, I have to turn the starter motor for 5 seconds because the fuel pump is not activated for 3 or 4 seconds when the ignition is turned on.

Additionally, I have the problem that the climacompressor sometimes doesn't work when I turn ignition of and restart the engine he returns work I read something that's its also a problem of capacitors Engine harness is new compressor is ok. GAS also

Thank you for reply
GREAT FORUM

 

[Alphasud40]

Yes, what you describe is the classic symptoms of capacitor failure. I take it this is a 92 module?

 

[gsxr]

Additionally, I have the problem that the climacompressor sometimes doesn't work when I turn ignition of and restart the engine he returns work I read something that's its also a problem of capacitors Engine harness is new compressor is ok. GAS also

This is not likely to be caused by faulty capacitors. The BM/GM module is what controls the AC compressor. Start by checking fault codes on this module (pin #8 on the 38-pin diagnostic connector).

 

[Alphasud40]

Yup, gsxr is right I didn’t see part 3 of your question. I had intermittent operation of my compressor as well. In my case the control unit pins must have developed some high resistance. Unplugging and reseating the BG/GM module a few times corrected this.

 

[Wosserlock]

Yup, gsxr is right I didn’t see part 3 of your question. I had intermittent operation of my compressor as well. In my case the control unit pins must have developed some high resistance. Unplugging and reseating the BG/GM module a few times corrected this.

Thank you, perhaps you are correct. Now it's better, and last week I did two things but I don't know which one was the right solution:

- I plugged and reseated the BG/GM and cleaned the pin and plug with some contact spray.

- I temporarily resolved the clicking of the relay and the starting problem by giving the relay a fixed ground on pin 85, so the fuel pump runs whenever the ignition is on (I'm aware it's not 100% safe, but it's just for testing and temporary).

Since then, the climate compressor has also been working well.

This is not likely to be caused by faulty capacitors. The BM/GM module is what controls the AC compressor. Start by checking fault codes on this module (pin #8 on the 38-pin diagnostic connector).

Thank you for your help as well.

I believe the function operates as follows: the LH Module checks the RPM difference between the engine and the climate compressor and sends a signal to the GM, where the relay that activates the clutch of the climate compressor is located. Therefore, I was thinking that a faulty LH Module could also cause problems with the Climate Compressor.

 

[gsxr]

I believe the function operates as follows: the LH Module checks the RPM difference between the engine and the climate compressor and sends a signal to the GM, where the relay that activates the clutch of the climate compressor is located. Therefore, I was thinking that a faulty LH Module could also cause problems with the Climate Compressor.

The LH module does not send any signal to turn the climate (AC) compressor on or off. The GM fully controls this.

 

[Wosserlock]

Hello, I have unsoldered all six brown/red capacitors and am now waiting for the new ones. However, I noticed another capacitor that is mounted horizontally (refer to the picture below). Is it necessary to replace this one as well?


Thanks everyone for the help

 

[Alphasud40]

No, I have checked them and they don’t seem to be bad.

 

[maw1124]

No, I have checked them and they don’t seem to be bad.

Did you also find that only the Fraco caps of that vintage are bad these days?

That looks like a blue Philips cap in the corner.

maw

 

[Alphasud40]

Yes, to date it’s only been the 22uf Frako caps that go resistive causing the problem with the fuel pump relay. I have seen open 100uf Frako caps but the control unit was still working fine. Meaning they lost their capacitance.

 

[Wosserlock]

Yes, to date it’s only been the 22uf Frako caps that go resistive causing the problem with the fuel pump relay. I have seen open 100uf Frako caps but the control unit was still working fine. Meaning they lost their capacitance.

Thank you, I can confirm this. I measured all the capacitors, and the 100µF capacitors are all OK; they have 118µF. However, the small ones are all bad. Just out of curiosity, does anyone have a circuit diagram of the ECU?

 

[Wosserlock]

Just out of curiosity, do you actually know what each capacitor is responsible for? I don't think they all just control the fuel pump relay, or what the problems could be if other capacitors fail

Thank you

 

[Alphasud40]

I never reverse engineered the circuit when I repaired these. I have 3 to do tonight. If I have time I will see if I can follow the traces. It’s more difficult with multi layered boards but I will see what I can do.

 

[Wosserlock]

If you could do that that would be great, but at least I know that there are instructions or repair instructions from Bosch for the new generations of control units where the components are also described, maybe someone has something like that or has access to it

 

[winmutt]

I have 3 (now 2) bad WOT LH modules for the 400. I bought the caps from mouser.com. Make sure you identify caps made for automotive (wider temp ranges). I tried to remove the caps with my solder iron but couldn't get them out and resorted to violence. With a pair of needle nose pliers the caps came off leaving the wire studs. Then with a solder wick and a cheap vacuum pump kit I got from microcenter I was able to remove the studs. The conformal coating gave me a bit of a challenge but I was able to replace the caps without much issue.

My early 91 LH (012) module is back in the car and running fine. I have two more 92 LH (014) modules which both have the fuel pump issues. Once repaired and tested I'll sell one. Included is a pic of mine pre surgery.

 

[Oldcar]

I wanted to add to this post since I am offering a LH capacitor update for forum members. So far in my observations the only LH that has the bad capacitors are the 92 models. It’s pretty easy to remove the LH from the module box and remove the circuit boards from the case using a T15 and a T10 screwdriver. If your caps are brown they need to be replaced sooner than later. The metal can caps all have been checking within tolerance so replacing them will just give you the piece of mind they won’t fail in the future.

Here is a illustration of what tools are needed. Flush cut cutter, T10 and 15 screwdrivers, a vacuum solder removal tool or solder wick, a small toothbrush to clean the rosen from the board after soldering, a good solder iron 20-30 watt with a fine tip, and good solder. I use the 60/40 rosin core solder that was used when the module was produced. The industry uses lead free solder which tends to be more brittle.
View attachment 185016



Here are a couple pictures of the original capacitors. Note the negative leads all face in the same direction and their values are printed on the top. Unfortunately QC has made marks over some of the values so in the next picture take note of the orientation of the 22 and 100uf caps.
View attachment 185018 View attachment 185019


You will see the upper capacitor is 100uf and the bottom caps alternate 100,22,100,22
View attachment 185021


In the previous post he mentioned the EPROM chip under this cover. This is the software written for this module. If you have a 92 WOT LH that has failed. This EPROM can be removed from its socket and be installed in another LH Module to retain the WOT feature.
View attachment 185022


You can see this is mounted in a socket and can be gently levered out. Take note of the notch on the end of the microchip and make sure you don’t reinstall backwards.
View attachment 185023


Just testing one of the old capacitors. These component testers came on the market a few years back. They can identify most active and passive components and it’s a cheap and quick way to test. I have some expensive test equipment and this is remarkably accurate.
View attachment 185024

As far as changing the components if you have never soldered I recommend you get a inexpensive kit to build before you tackle this job. The removal method I use is I heat the solder joint while gently rocking the capacitor to free it. Then I alternate back and forth until the leads are free. Then I clean my iron tip and apply fresh solder to the tip and heat the hole while simultaneously drawing the solder from the hole with the pump. Then it’s just the matter of installing the new component and soldering the leads. Then remove the rosin with alcohol and a clean rag after giving it a scrub.

Alphasud40 did my 92 m119 lh module
And it runs so smooth now it is almost boring. Seriously it purrs like a cat!
I was told high gear is attained after 90mph I wonder how smooth it would be cruising at 120 @ around 2800 rpm not that I have ever exceeded the legal speed limit! Car runs tits now...
..

 

[gsxr]

I was told high gear is attained after 90mph I wonder how smooth it would be cruising at 120 @ around 2800 rpm not that I have ever exceeded the legal speed limit! Car runs tits now...

4th gear (actually, all gears) engage based on vehicle speed and throttle position. The transmission does not remain in 3rd gear below 90mph.

On a 400E with USA-spec 2.24 gearing, 90mph in 4th gear will be approximately 2800rpm... 120mph will be around 3750rpm.

 

[emerydc8]

4th gear (actually, all gears) engage based on vehicle speed and throttle position. The transmission does not remain in 3rd gear below 90mph.

Is it speed or a function of vacuum. I ask because I am trying to figure out where the transmission would get a speed input, specifically for downshifts when coming to a stop.

 

[Unavita]

God bless those who had the space and place to tear apart electronic battle ship in their you and damage the board with the solder! AND that kept up this smoldering task.

I once had stiches on a finger that looked like a road map. An old doc did it. I went back to get it repaired that night. A younger doc did that. I would be the former!

#goodstuff!

@gsxr

 

[Unavita]

Is it speed or a function of vacuum. I ask because I am trying to figure out where the transmission would get a speed input, specifically for downshifts when coming to a stop.

(FOR Newbie's not familiar with the 722)
What year car? 4 speed or 5 speed autobox. Only speaking for the 4 speed here/hear: (Please correct if I err) the 4 speed receives it's vacuum from the (intake) manifold via a white vacuum line at the rear of the manifold that goes to the modulator on the driver side (US) of the transmission. The adjustable modulator controls when and how hard the trans shifts for the most part (without changes to the valve body) - and the solenoid on the passenger side. ADDITIONALLY the throttle adjustment- when examined closely- will show you that it is directly connected to the above mentioned solenoid.
IN ADDITION: The LH module controls shifting as well: take it from here @gsxr!
(I THINK HE ^ IS GOING TO SAY "ONLY WHEN SPEAKING OF FIRST GEAR START AND SECOND GEAR WARM-UP DELAY. Which I think is adjustable in the LH module by essentially telling the ecu (cough cough) that it is warm enough already to shift from second AND/ OR (lawyers frown) the loud pedal has been smashed for a first gear start: something Mercedes determined would hamper the life of the 722 on cars producing 300+ ft. lbs. of tq. JUST GUESSING.

I believe the correct answer to the "when coming to a stop" is, depends.

 

[gsxr]

Is it speed or a function of vacuum. I ask because I am trying to figure out where the transmission would get a speed input, specifically for downshifts when coming to a stop.

Vacuum only affects shift firmness (it's an estimate of throttle opening / engine load).

I believe the transmission gets the speed input from the centrifugal governor assembly, behind the cover at the rear/driver side. If you have time to read in depth, the factory technical design document is here.

 

[R129 UK]

If you have time to read in depth, the factory technical design document is here.

Peak geek in that link

 

[dam234]

Alphasud40

Can you tell me what kind of integrated circuit this is? What are its markings?

Best Regards
Thanks

 

[Oldcar]

Oviously gsxr and alphasud40 are quite knowlegeable they helped me with the lh rebuild and identifying vacum source

 

[Alphasud40]

I can’t see the markings in the photo but as GSXR stated you are better off finding a replacement module. Also not the EPROM chip that holds the software can be swapped from your old to the new module since this looks like a WOT LH ECU. Most of the components are proprietary and obsolete.

 

[Jamesc4772]

I can certainly look at the module for you but to the best of my knowledge the HFM module didn’t suffer from bad capacitors. If you haven’t pulled codes in the modules that would be your next step. If the car hasn’t run in a long time there could also be other factors like old fuel or incorrect fuel pressure causing issues. The module could have been damaged from a shorted harness. I could look it over for burnt drivers.

Help me with my module! Just bought a 1992 400e. Need my module repaired!

 

[Oldcar]

Help me with my module! Just bought a 1992 400e. Need my module repaired!

Alphasud and gsxr .....that's all I have to say about modules...they are the gold standard

 

[Oskichohfi]

Hello everyone, could you give me a hand? I have a module of e420 0175454432, I replaced 5 capacitares, 3 of 100uf 50v and 2 of 22uf 50v.

The 100uf ones were bad, the others weren't, but they replace them anyway. The problem continues, the rele is directly armed. Does anyone know how to solve it? Thank you.

 

[gsxr]

The 100uf ones were bad, the others weren't, but they replace them anyway. The problem continues, the rele is directly armed. Does anyone know how to solve it? Thank you.

Can you explain in more detail the problem, "the relay is directly armed"?

 

[Oskichohfi]

That's right, he's armed directly. He doesn't arm and disarms. I thought it was the caps.

 

[TerryA]

@Oskichohfi,
I don’t remember seeing any mention of a relay in my 16 years on this forum.

Maybe I’m thick headed but IMOP your answer didn’t clear up gsxr’s question. I think you (or someone) needs to explain what the relay does (what it controls) and maybe point out where it is in your photo.

 

[Oskichohfi]

The module has the pump relay activated directly when it turns on the ignition. It was to turn on and off after 1 second.

I thought it was the capacitors with a problem. The 100uf ones were really bad. Around 50uf. The 22uf ones were good. But I changed it anyway.

I would like to know if anyone has ever been through this?

I know it's a problem with the module because I borrowed another one and the rele worked perfectly.

Sorry if I wrote something wrong. I'm using google translator

Thank you.

 

[gsxr]

Ah, ok, the fuel pump relay. You are correct, the relay should turn on with the ignition for 1-2 seconds, then turn off. And, the relay should remain on (not clicking) with the engine running.

Since a different LH module you borrowed worked correctly, it sounds like there is something else wrong with your module besides bad capacitors. You could try also testing / replacing the 2 green capacitors on your circuit board, but I don't know if that will fix the problem.

I'd buy a good used LH module, the 4.2L modules are relatively inexpensive. Click here to see one example on eBay.

 

[Oskichohfi]

I took out the 22uf 10v green tantalum capacitor and tested it. He's bad too. I hope he's the problem. I'm waiting to arrive to replace it.

The other green 33uf capacitor is good.

I'll let you know if it works.

Thank you for your help.

 

[Oskichohfi]

Hello everyone.

Good news.

I replaced the 22uf 10v capacitor with another one like it. The capacitor is tantalum drop.

Solved the problem. Now the pump turns on and off after 2 seconds.

Thank you all for your attention.