Don't throw away your LH2.4 module yet - Hybrid module repair might be underway

Hi All,

For my personal Turbo conversion project I have also ran into the issue with the 56x series ECU's and their slow failing due to the hybrid module rosin cracking, resulting in a approximate 15 year shelf life, and many many headaches.

After many internet searches and some investigatory reverse engineering I came across this site, for repairs on the Porche LH computers: https://home.kpn.nl/mirjam_paul/928_lh_repair.html

So I gave him a call, turns out the hybrid module can be replaced by a more foolproof reversed engineerd version without the issue of open to air silicon chips. I asked him if the chips were universal, to which I got the suprising answer that Bosch decided to change them for each revision (Still supspicious of this, will try to confirm soon, with comparison of 563 and 984 ECU hybrid modules).

Since I am currently studying to become an electrical engineer, and also up for a challenge, I created this thread to work together on a solution for our LH2.4 and LH2.2 cars, which would probably come in the form of a cheap affordable diy kit.

Where do we start

To get an idea of the feasability of this project, I need reference pictures of the hybrid modules of several ECU's to compare them, and asses the compatibility. The hybrid module is the white square on the printed circuit board on the right as seen in the picture below.



It would also be helpful to get some information about the ECU with the picture:
ECU number - 0 280 000 xxx
Year of production - 19xx
Engine model/type - b230xx

But why? Isn?t an eBay ecu of later vintage pretty cheap, likely cheaper than a mail away fix?

Are you referring to the known issue of having false codes? I have encountered the 561 ecu giving false codes and replacing them with a white label 561 or a 951 solves the issue.

If you can come up with a fix for the ecu that gives false codes. That would be great.

Wish you well with the project.

I have a 951, 561, 937 and possibly 946 that I can document for you, maybe not this weekend but next. First two are from 1991 240s with B230Fs, the third is out of my 1993 940 B230FT without EGR, and the last is out of a 1991 240 with B230F and EGR.

Interesting project, but, unlike vintage Porsche owners, old Volvo Owners won't spend any $$$ to keep it original. Around here, a salvage yard ECU goes for only $14.99 ("Control Module"), plus 10% enviro fees. And the newer 9xx series ECUs can swap in for the problematic 5xx series so there's no shortage of ECUs.

Looking through my parts pile, I see at least 2 different versions of the hybrid module. Using your picture, if you look at the upper left side of the hybrid, you'll find a hybrid substrate number, and if you look at the bottom edge, you'll find what looks like a build or parts stuff number. My scrap 937 has a substrate # of 129-1 and a build # of 132. This is different than the 5xx series.

PhysSDK2 said:

But why? Isn?t an eBay ecu of later vintage pretty cheap, likely cheaper than a mail away fix?

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Hi, yes for now it would be, but since most hybrids last 15 years, at some point you would end up with a limit to the alternatives.

dl242gt said:

If you can come up with a fix for the ecu that gives false codes. That would be great.

Wish you well with the project.

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Hi, the problem I'm am referring to is the issue where the communication module from the 5v processor for the 12v car circuitry fails. I am not too sure if it would be related, but maybe it could trick the diagnosis functionalities.

redblockpowered said:

I have a 951, 561, 937 and possibly 946 that I can document for you, maybe not this weekend but next. First two are from 1991 240s with B230Fs, the third is out of my 1993 940 B230FT without EGR, and the last is out of a 1991 240 with B230F and EGR.

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That would most definitely help, my suspicion is that the modules only vary between the first digit in 5xx, 6xx etc. Would be nice to have somewhat close to confirmation.

bobxyz said:

Interesting project, but, unlike vintage Porsche owners, old Volvo Owners won't spend any $$$ to keep it original. And the newer 9xx series ECUs can swap in for the problematic 5xx series so there's no shortage of ECUs.

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Yes to this I agree, however for adaptability the 5xx are much preferable, the later series were adapted for finer control, however with the same basic processor sacrifices were made in other functionalities.

bobxyz said:

Looking through my parts pile, I see at least 2 different versions of the hybrid module. Using your picture, if you look at the upper left side of the hybrid, you'll find a hybrid substrate number, and if you look at the bottom edge, you'll find what looks like a build or parts stuff number. My scrap 937 has a substrate # of 129-1 and a build # of 132. This is different than the 5xx series.

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Yes this I already noticed when troubleshooting my own ECU since I had a 984 laying around which was not a direct swap, I am focusing on the 5xx for now, and after the process is set and known the rest should.be quicker.

Also something to be kept into account once more is that all hybrids crack eventually, and with the tunability of lh2.4 and the many bricks around the development of a cheap kit would probably be worthwhile

Swedbrick said:

That would most definitely help, my suspicion is that the modules only vary between the first digit in 5xx, 6xx etc. Would be nice to have somewhat close to confirmation.

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About 15 years ago, some of us 240 aficionados hypothesized the label color had some significance when the -561 ecu was discovered to have a weakness in the hybrid's fuel pump switch. Pink label = weak hybrid; White label = no problem. An informal survey ensued convincing us it was true; that Bosch and Volvo quietly slipped in improvements without part number changes. The white label -561's employ the same revised hybrid as the -951's we saw as rock-solid replacements.

Several theories come up as to the failure mode of the old colored-label 5xx hybrids when they stop pulling in the fuel pump relay, including the one you mention where the gel coating allows contaminant migration, and the eventual failure of the fuel rail grounding separating signal and power returns. Whatever the real cause is, the new hybrid modules, which you can see identified here https://www.brickboard.com/RWD/volvo/990665/220/240/260/280/will_561_ecu_work_place_951.html seem to solve this problem regardless of how old they've gotten. In fact, someone in Germany was buying up every white-label LH2.4 ECU one of our friends could dig out of the yards here in US. I've also seen where one of the rebuilders has gone to the trouble of creating their own discrete-component drop in replacement for the hybrid, but I haven't heard anything nice about it.

I've only seen two versions of the Bosch hybrid myself.

Edit: Just realizing the close look at these hybrids ignores about 15 years of my experience. These images of the only two versions I've seen are from 2003. http://cleanflametrap.com/561bad_lg.jpg http://cleanflametrap.com/561good_lg.jpg The numbers mask printed on the substrate of the newer hybrid match that in bobxyz's post.

Alright, the plot thickens, form what I have seen in my own ecu's, the white label hybrids are not all the same, but if Bosch also had revised versions, best to reverse engineer those. I'm hoping to create a discrete version, but my aim was to make it the same size, so maybe for stability it would be nice to include a micro-processor to remove most of the analog instabilities.

Edit: Maybe those bad experiences where due to inferior component choices, I used to repair consumer electronics for some extra income, and most failures were due to cost savings by using sketchy brand components, failing after 3-5 years.

So you are considering making a hybrid interface chip using a micro controller? I used to work with micro chip brand controllers on vending controllers and smart safe controllers. It was good work while it lasted. Seems like that hybrid is the major failure in these and you have a good idea what to do. Looking forward to what you come up with.

Which part on the board is it exactly? I got some reman boards look like they got different chip on it for sure also. From Florida, programma I think they are called. I think it's already been done, I'll post some pics. I know I got one programma one says 561 on the outside but inside motherboard says 951.


Also that 984 ECU is a immobilizer ECU won't work without the correct key and harness unless you put say 967 chip in it. Then it will work. It's the last ECU made, it's actually OBDII plug to read codes, 1998 turbo b230ft.

Honestly, you could do all of this with an arduino, a breadboard, some capacitors, resistors and a transistors so $30 plus idk a billion man hours reading timing signals? Of course the system is very old, maybe if you contacted Bosch they’d give you the circuit diagram at this point. You could also try to X-ray and dissect some of the modules to figure out exact components. Idk if any on the chips are custom asics that’d be the hard part, but an arduino or something like that is several orders of magnitude more powerful and reliable than anything of the time. Hell, I bet you could breadboard an entire replacement ecu running Linux in real-time mode with 1/50th the components.

It’s a lost cause, but I wish you luck but maybe you’ll get a job out of it.

Yeah ain't nuthin to it see it done already just a couple 'O' surface mount caps and resistors and a breadboard, glutten free of course.


I'm wondering how this has anything at all to do with LH 2.2 as the original poster said it did??

$550 for a microsquirt pnp solution to replace the LH2.4.
http://forums.turbobricks.com/showthread.php?t=144251

sbabbs said:

Yeah ain't nuthin to it see it done already just a couple 'O' surface mount caps and resistors and a breadboard, glutten free of course.


I'm wondering how this has anything at all to do with LH 2.2 as the original poster said it did??

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I have one of these on the shelf in my garage also... From a 1990 740 NA with EGR. Will take a pic of its gut and will report back.

Thanks Simon, that's a very interesting picture. Based on the large number of small parts visible on the top of the replacement hybrid module, and what the original module looked like, I'd guess that there are a few op-amp and comparator chips hidden on the bottom of the module.

Also interesting is that it's a 951 pc board (see the 951 in black silkscreen paint in lower right), but the label on the case is for a 561. The pc board shown does NOT have provisions for a 561 cold start injector -- it should be the 2nd power transistor up from the bottom on the heatsink, but it's empty in your picture. Makes me curious if the ECU is really a 951, but labelled and sold as a 561 replacement. I also wonder what firmware is in the PROM, 561 or 951?

programatools.com looks like they're still around in Florida as http://www.programainc.com. They list rebuilt 951 ECUs on special for only $129 (maybe inventory closeout???)

[For you electronic geeks, here's some more info on the hybrid and hybrid replacement:
Starting with Art's hybrid picture here: http://cleanflametrap.com/561good_lg.jpg
- this is a thick film hybrid, a somewhat common high-density technology from the 1970s.
- the white background material is a 2 layer ceramic
- the light tan lines are metalized traces
- the black rectangles are resistors -- they're silkscreened on with resistive paste
- silkscreened resistors have awful tolerance initially, maybe 30% or more off from desired.
- silkscreened resistors are normally laser trimmed to very tight tolerances (say 0.2%). If you look at the picture carefully, you can see white lines or "L"s in the black resistors. These are the laser trim lines that adjust the resistance to the desired value.
- the tan surface mount chips are capacitors
- the 2 blobs under the black cross-hair frames are bare silicon chips. The gold rectangles around the center chips are wire bond pads. If you look carefully, you can see really tiny gold wires going from the bond pads to the bare die.
- I scraped the goo off one of the chips on my scrap hybrid and looked at it under a 30x microscope. The bare chip is ~35 pins and has the Bosch logo on it, so I'd guess a custom analog part.
- There aren't enough pins on the hybrid for a microprocessor bus, so any A-to-D conversions must be done in the processor, not the hybrid.

Looking at the hybrid in Simon's picture:
- the 2-pin black and blue chips are resistors
- the 2-pin tan chips are small-value capacitors (ceramic)
- the 2-pin bigger yellow chips with a tan band are larger value polarized caps (tantalum)
- the 3-pin black chips are transistors
- not sure what the black chip is at lower left
- on the main 951 PCB, the empty space for a square chip in lower left (with all the empty solder pads) is populated with a quad 600mA power driver chip (CA3272) on the later 940 ECUs. This drives the high&low fan relays, plus the fuel pump relay. On the earlier ECUs, the fuel pump relay was driven from the hybrid.
- of the reported 5xx ECU failures that I've seen, I believe the fuel pump related ones, and expect that the re-designed hybrid "fixed" the fuel pump circuits.]

Hey guy's, sorry for the lack of response lately, currently graduating and all that

dl242gt said:

So you are considering making a hybrid interface chip using a micro controller? I used to work with micro chip brand controllers on vending controllers and smart safe controllers. It was good work while it lasted. Seems like that hybrid is the major failure in these and you have a good idea what to do. Looking forward to what you come up with.

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Hi, yes that would probably be doable, a bunch of dac's and all of the scary analog responses would probably be gone. If all goes well, I get to reverse engineering the whole hybrid this winter somehow:')

sbabbs said:

I think it's already been done, I'll post some pics. I know I got one programma one says 561 on the outside but inside motherboard says 951.

Also that 984 ECU is a immobilizer ECU won't work without the correct key and harness unless you put say 967 chip in it. Then it will work. It's the last ECU made, it's actually OBDII plug to read codes, 1998 turbo b230ft.

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Hmm, that would make sense, wonder if the previous engineer still has the stuff around. Concerning the 984, yes thanks, I already figured that out, currently running a na computer, I'll be investing in a burner and some eeprom's soon, to get a -967 bin running.

PhysSDK2 said:

It?s a lost cause, but I wish you luck but maybe you?ll get a job out of it.

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I can agree, but since I'm planning to build my own ecu eventually, it's good practice

bobxyz said:

programatools.com looks like they're still around in Florida as http://www.programainc.com. They list rebuilt 951 ECUs on special for only $129 (maybe inventory closeout???)

- There aren't enough pins on the hybrid for a microprocessor bus, so any A-to-D conversions must be done in the processor, not the hybrid.

- of the reported 5xx ECU failures that I've seen, I believe the fuel pump related ones, and expect that the re-designed hybrid "fixed" the fuel pump circuits.]

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Hi, thanks for the contribution of such a host of info, I'll try to contact programatools, maybe they are willing to let go of some schematics/manuals!

As far as the a-to-d conversion part seems, that would make sense, the hybrid converts from the 5v tot the 12v level, however the reverse conversion from 12 to 5 is simply done with a divider. As part of my graduation project I've had to implement this for a datalogger.

For the pump failure, I believe to recall the porsche expert to have confirmed this often goes along with diagnosis port failure, which my -563 has also shown along with the fuel pump driver not functioning whilst the driver circuit up untill the driver checks out.

This old paper (pre LH2.4) might provide some insight into the hybrid circuits: downloads.hindawi.com/journals/apec/1981/243687.pdf

Looks like the earlier versions implemented an analog multiplier and an analog divider on a hybrid.

I did read the programma chip, PM me if you want me to email it to you. It was the same as stock except it did have a little bit or two change in the fuel map I think. CAn't remember off hand if it was 951 or 561. I think I have one of each from programma actually.

I can tell you the basics the hybrid does as far as I can remember:
1. K-line interface for diagnostics
2. 12v-to-5v and vice versa level shifter for different inputs/outputs
3. Precision 4.96v regulator for the ADC reference
4. Watchdog connected to the MCU reset line. The firmware must feed it with frequent pulses to keep running, otherwise watchdog asserts the reset.

I have somewhere reverse engineered pinout of the hybrid, if I can find it I will post it here.