A fifth "non-CAN-box" computer (Diagnostic Module)

[gerryvz]

Is anyone familiar with the function of the "CARB" computer, which is found in the passenger footwell of the E500E and the 400E/E420, among many other 6-, 8- and 12-cylinder cars of the early-mid 1990s?

It's a silver, metal-enclosed box that is about 2/3 the size of the CAN-box computers, except that it sits in the footwell. The computer is marked "CARB" "Made in Germany" and has the MB part number 015 545 13 32, Bosch part number 0 261 200 916. It's not cheap - the list price on the lil' guy is $1,450....

I believe it has something to do with ignition and fuel injection control, and it is linked in with the CAN-bus computers. But I don't know specifically what it does, so am really interested if anyone can shed light on this.

Cheers,
Gerry

 

[DerFuror]

Re: A fifth "non-CAN-box" computer

EPC calls it a Diagnosis Control Unit & has it listed with the CAN box items in Grp 54 SubGrp 080

 

[Ron500E]

Re: A fifth "non-CAN-box" computer

CARB is the California Air Resources Board. The module appears on all "California" 036s. Which means "all" US 036s since I believe all US cars were built to "California" specs.
California has stricter emission laws than the rest of the USA so car makers offer, or did, a special version for that state.

The module is for diagnostic purposes only I believe.

Kind Regards,

Ron

 

[gerryvz]

Re: A fifth "non-CAN-box" computer

My understanding of this module is that it monitors the CAN-bus computers, and also has the ability to throw the car into limp-home mode if some programmed parameters aren't met. Some further research shows that it has ignition control capability. I'm just trying to discover more as to WHAT it does and HOW it interacts with/monitors the other computers, and WHY it's in there.

You are correct that ALL NEARLY ALL US-market 036s were/are California-compliant (i.e. "50-state" cars) as shipped from MBUSA.

Other cars did have this identical box, such as the R129 and other W124s. I believe that 8- and early 12-cylinder W140s also used it.

Cheers,
Gerry

 

[J-Sauce]

Re: A fifth "non-CAN-box" computer

Gerry, are there not some exceptions to that rule? My car was originally sold in Indiana (US), and has no CEL as well as no DTC blinker box. I believe there are a few other examples of this, although rare. Build is 11/91. I will check for this computer soon and let ya know if it is included in even Federal cars like mine.

 

[gerryvz]

Re: A fifth "non-CAN-box" computer

Yes, if I remember correctly, I believe Normal Aiello ("Cannoli" on the forum) also has a car that is similar to yours. And I seem to remember his also being a very early car too. There may be some exceptions but the vast, vast majority of the US 036s are 50-state cars. So yes, I was over-generalizing just a tad bit with this statement. In most cases though, it is definitely true.

Cheers,
Gerry

 

[samiam44]

Re: A fifth "non-CAN-box" computer

Is that the diagnostic module for US CEL?

 

[gsxr]

Re: A fifth "non-CAN-box" computer

Yes, that is the Diagnostic Module (DM), error codes from this module are available via pin #19, or from the built-in blinker in front of the CAN box.

This module is ONLY used on cars with a Check Engine Light in the instrument cluster. It was not present on some very early build 1992 500E's in the USA. My '92 500E (08/1991 build) and Justin's car are two examples.

 

[Cannoli]

Re: A fifth "non-CAN-box" computer

Yes, if I remember correctly, I believe Normal Aiello ("Cannoli" on the forum) also has a car that is similar to yours. And I seem to remember his also being a very early car too. There may be some exceptions but the vast, vast majority of the US 036s are 50-state cars. So yes, I was over-generalizing just a tad bit with this statement. In most cases though, it is definitely true.

Cheers,
Gerry

This will cost you Gerry the next time we see each other again ... a bodaciously smooth bourbon will be servered neat!

I'm not Indian nor Paki ... it's "Norman", which is a name common in Sicily - it literally means a "North Man" i.e. Viking - ala the Normans, who once occupied Sicily. And for the record, I'm a Sicilian American with other connections in the Italian environs.

Back to our topic ... I have a 1992 "US FEDERAL" homologated car ... NO Check Engine Light .... NO DM... NO CARB crap. Amen.

 

[Stevester 500E]

Re: A fifth "non-CAN-box" computer

The Carb computer looks to have two switch positions.
Does anyone know what the two positions are meant for?

 

[Klink]

Re: A fifth "non-CAN-box" computer

The Carb computer looks to have two switch positions.
Does anyone know what the two positions are meant for?

It's not a switch. You turn the knob to to release or lock the control unit into it's terminal base.

 

[Klink]

Re: A fifth "non-CAN-box" computer

Just FYI for those that possibly don't yet know, the CARB box is just that, Cali Air Resources Board. This is the device that made the vehicles it was installed in "OBD1" compliant. It doesn't alter or control anything, it mostly monitors emission related self tests that the various systems already perform, then organizes and logs the results for a somewhat more standardized (for the times) emission fault diagnosis. Most importantly to the regulators, it illuminates the "Check Engine" warning lamp, causing immediate failure of some local and state emission tests, and supposedly prompting the owner to have the situation rectified. On some models, some additional sensing elements and related items are added for the CARB unit to monitor. I think that some can add or "ask for" the control units to perform a certain test, but it does not alter any operating parameters of any of the systems. That being said, one that is malfunctioning can cause mischief. It is rare, but I've seen one or two cause the CAN data bus to be shut down. That was very early on when these were new. I haven't seen one act up in such a manner for many years...

 

[Maui]

Re: A fifth "non-CAN-box" computer

I had to replace one after a minor short circuit checking codes. I stuggled to figure what was wrong with my 500E and finally replaced this little box and all the issues were solved. So, yes it can cause mischief.

 

[gsxr]

Re: A fifth "non-CAN-box" computer

I had to replace one after a minor short circuit checking codes. I stuggled to figure what was wrong with my 500E and finally replaced this little box and all the issues were solved. So, yes it can cause mischief.

I had one fail a number of years ago. IIRC, the symptom was the CEL on but no codes and no communication with a digital scanner, and the module itself was warm to the touch in a cold car. Swapped it for a used module and everything was kosher again.

Klink's explanation is dead accurate, btw! If you don't need this thing for emissions where you live, it could be removed from the car. I prefer to leave it functional as I'd like a visual indication on the dash if something is awry under the bonnet.

 

[gerryvz]

Another good item to have as a "spare". Fortunately they are very common on wrecking-yard cars, and if you see one on any late W124 model I'd definitely snag it.

 

[captruff]

Another good item to have as a "spare". Fortunately they are very common on wrecking-yard cars, and if you see one on any late W124 model I'd definitely snag it.

I happen to have several of these diagnostic modules if any member is in need.

Jeff

 

[SG-Motorsports]

Also an FYI, this Diagnostic Module is similar to the same unit used on the M104 equipped 124 cars. As klink mentioned it is only for storing data and turning on the check engine light. It can sometimes be useful for diagnosing a problem because of the fault codes stored, but otherwise has no control over function/tuning of the engine. It can be disconnected and removed with no ill effects, the engine will run completely as normal with it removed. There are several cars running around with this module unplugged because people don't want to fix (ie too cheap) their 'check engine' lights and it's easier to unplug the module than pull out the bulb.

 

[markob]

Can the diagnosis still be performed without the CARB Module? I ask because the one in my car is bad and the car just doesn't even start when it's connected but runs perfect without it.

 

[captruff]

Can the diagnosis still be performed without the CARB Module? I ask because the one in my car is bad and the car just doesn't even start when it's connected but runs perfect without it.

I have an extra one if you want to replace.

015 545 13 32

Donor car was a 1995 E420

$30.00 delivered to the lower 48

Jeff

 

[markob]

I have an extra one if you want to replace.

015 545 13 32

Donor car was a 1995 E420

$30.00 delivered to the lower 48

Jeff

Absolutely, Is the a way to PM? I can paypal or venmo

 

[gsxr]

Can the diagnosis still be performed without the CARB Module? I ask because the one in my car is bad and the car just doesn't even start when it's connected but runs perfect without it.

The DM module can be completely removed and the car will run & drive perfectly. You'll just lose the CEL function, which may be an issue for emissions inspections, if required where you live.

I'd pick up the spare from Jeff just to get it fixed properly. Easy enough to swap out.

 

[captruff]

Absolutely, Is the a way to PM? I can paypal or venmo

Paypal: captruff@gmail.com

Please send me your name and address in the note section or PM me here on this site.


Jeff

 

[markob]

Sent PM