OBD on a 420SEL? - PeachParts Mercedes-Benz Forum

Panzermann · #1 06-12-2006, 10:13 PM

While I know that a 1991 420SEL was prior to the initiation of OBD II, is there a way that error codes are stored in the car and I can get access? ?OBD I?

Jim B. · #2 06-13-2006, 01:20 AM

It could be possible that OBD I codes are there. I have a '91 coupe and
someone did run them for me once. But it was long ago. I vaguely recall a small black box near the middle of the outer firewall that held the secrets- but not sure of it. The codes would flash small red lights in a specific sequence to identify the fault.

I DO remember the last time the car was in the car, last month, the mechanic told me that he would rather run the codes in the W126 because there were only 9 of them whereas he would rather avoid running them on the W140 S class (I think he said there are 32 of them) and would prefer not to wrench the W140 series cars at all

As I said , I'm not sure of all of this, those are just my recollections, but I think they are on the right track

pcmaher · #3 06-13-2006, 07:39 AM

My good friend Jim F has an excellent webpage that will help you out...

http://pages.prodigy.net/jforgione/MB_X11.html

This may be of some help too...

http://v12uberalles.com/pulling_codes.htm

Panzermann · #4 06-13-2006, 04:15 PM

Quote:

Originally Posted by Jim B.

It could be possible that OBD I codes are there. I have a '91 coupe and
someone did run them for me once. But it was long ago. I vaguely recall a small black box near the middle of the outer firewall that held the secrets- but not sure of it. The codes would flash small red lights in a specific sequence to identify the fault.

I DO remember the last time the car was in the car, last month, the mechanic told me that he would rather run the codes in the W126 because there were only 9 of them whereas he would rather avoid running them on the W140 S class (I think he said there are 32 of them) and would prefer not to wrench the W140 series cars at all

As I said , I'm not sure of all of this, those are just my recollections, but I think they are on the right track

So does this mean that the thing for the lights is already in the car and you just have to push a button?

autozen · #5 06-15-2006, 11:28 AM

Since you live in Arizona, you probably have a Federal car and won't have the button and light. If you by chance have a California, you will have both. If you have a Federal car, you will need a scanner. Also if you have a fuel pump relay, you only need to pull codes from the CIS computer. If you have a MAS unit, you will need a breakout box or find some way to back probe pin #14 on the MAS unit. If you only have a CIS computer with fuel pump relay built in, you only need to pull codes from the computer. As an additional bit of info, the only thing that will make the CEL go on in a Federal car is a problem with the O2 sensor circuit.

Panzermann · #6 06-16-2006, 12:41 PM

Quote:

Originally Posted by autozen

Since you live in Arizona, you probably have a Federal car and won't have the button and light. If you by chance have a California, you will have both. If you have a Federal car, you will need a scanner. Also if you have a fuel pump relay, you only need to pull codes from the CIS computer. If you have a MAS unit, you will need a breakout box or find some way to back probe pin #14 on the MAS unit. If you only have a CIS computer with fuel pump relay built in, you only need to pull codes from the computer. As an additional bit of info, the only thing that will make the CEL go on in a Federal car is a problem with the O2 sensor circuit.

Car was originally sold to my Dad in CA from Downtown LA Motors, so I presume it is CA-emissions.

skiier3_9 · #7 06-16-2006, 04:30 PM

Take a look under your hood on the firewall near the battery. There should be an 8 pin diagnostic socket. You can use Arthur Dalton's code reader to access codes on any of the pins (that have sockets). If the car is indeed a CA car, it will have an LED and switch built in to read codes from the CIS-E/emissions system (pin 3 if you're using the code reader).

with the ignition on engine off, press and hold the sw. for 2-3 seconds, release the switch and count the number of blinks of the LED. Record the number of blinks and repeat until you get the same number of blinks a second time (the codes are read out in sequential order)

Panzermann · #8 06-18-2006, 10:12 PM

I tried it. You have to do it with the engine off, but key in ignition. Indicated a single flash, meaning no codes stored (turned out the Haynes Manual at the local autoshop described the procedure). Sort of neat to be able to get the 411 without needing a code reader. Wonder why they only included this feature in the CA emissions version of the cars and not elsewhere.

autozen · #9 06-19-2006, 06:35 AM

Quote:

Originally Posted by Panzermann

I tried it. You have to do it with the engine off, but key in ignition. Indicated a single flash, meaning no codes stored (turned out the Haynes Manual at the local autoshop described the procedure). Sort of neat to be able to get the 411 without needing a code reader. Wonder why they only included this feature in the CA emissions version of the cars and not elsewhere.

Considering the fact that CA has more cars than any state in the union and the fifth largest economy in the world, it would be impossible to breath if auto and factory emissions weren't controlled. We have CARB ( California Air Resources Board) which imposses the toughest laws in the country.That is why cars are divided into Ca cars and 49 state cars. We have always had the toughest auto emissions testing, but changing federal laws are mandating the same sort of testing in all states.

Also Californians always push for more control of their daily lives as exhibited by the fact that you can go into a store in San Francisco and buy medical mariuana (sp) for pain if you have a doctor's note. This is driving the feds crazy. When those cars came out with test points Ca said owners should have easy access to the codes.