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1996 Mercedes SL500 smog OBD not getting ready

16K views 97 replies 11 participants last post by  355190E26 
#1 ·
I went thru most of posts related to this issue but something I could not understand yet. So here I came back. after smog test with emission PASS, I was told to go thru Drive Cycle and tried many times and took my car back to STAR Diagnostics but still not ready. Something wrong with car while it does not have any codes. Their scanner clears only 3 items on the screen and the rest remain with * (not ready).
I did replace a few things last year such as both position sensor, fuel pump, fuel filter, oil change, engine belt, overhaul power steering pump ( I only remember these). And I removed the SRS light bulb from the instrument panel. And after I replaced oil with 0W-40 instead of 10W-40, I start getting intermittent oil pressure gauge warning light.
Now, what I have to find out is what is stopping the OBD from getting ready for the smog test. Did I make any mistake in installing all the above or something disconnected to communicate with OBD system.
Anyone has the circuit diagram for entire EMC to OBD inlet? Or had same problem and resolved this issue?
Like always, I appreciate your help again.:nerd
 
#2 ·
Did I make any mistake in installing all the above or something disconnected to communicate with OBD system.
The OBD II system is reporting statuses and communicating perfectly, and your past work probably has nothing to do with your problem.

Their scanner clears only 3 items on the screen and the rest remain with * (not ready).
I suggest you reply back with the specific tests that are displaying "not ready".
 
#43 ·
Star Diagnosis result



Yes, my 96 SL500 passed the emission test but failed on functionality test, which I was told OBD is not getting ready for test, and for which I was told to go thru Drive Cycle.
No diagnostic codes at all.
Numerous attempts of Drive Cycle without success. Something is inhibiting the communication of this OBD II and not getting ready for the full test.
 
#6 ·
there are drive cycles and there are drive cycles. for some requires up to 30 minutes of driving including speeds in the 50mph range. others require a short drive cycle with lots of stop and go. some require mulitple start restart cycles coupled with a drive pattern. Some require multiple starts from cold. it all has to do with the diags verifying that there are no parameters going out of bounds unexpectedly.

for each of the tests that aren't set a good indy will be able to look up and see what the required drive cycle is.
 
#12 ·
Read what Bob posted carefully. It requires nothing special. Or just drive the car, long and short, for a long time, like 2 weeks, WITHOUT scanning and resetting errors. Each time you reset, you start over. 96's are a beooch, early obd, and mine did this. 3 weeks at the indy til it was ready.
 
#13 ·
OMG, stupid of me. Now I remember I did erase the codes using my AUTEL scanner last year after I replaced fuel pump and fuel filter. I simply did not know that I shouldn't.
I have been driving more than 4,000 miles since then. Now I need to go thru this step. WOW.
Still, I believe this OBD II requirement is pain in the butt. I will cool off a little while and get on to this.
Thanks to all and I will let you know.
 
#14 ·
I guess I still live in old age without much of late model car electronics and I feet puked by this issue. My car is running good and passed the emission but OBD not getting ready after driving more than 4,000 miles?
I am still waiting for right time to go through this DRIVE CYCLE that Bob posted.
Few things on the instruction put me into darkness but I will go through as much as I can to see what happens.
I bought the AUTEL scanner last year to diagnose the fuel line and erased the error code after I replace pump. I know it caused this problem. But somehow I have a feeling there must be someway to reset the OBD in order to get communicated.
Anyone have any suggestion?
 
#17 ·
I had the same with my car, even I drove 400 miles and I was making different driving habits for the purpose. '
Than I went on the net to find the requirements and it said to idle the car for couple of minutes.
My normal habit is to take less than 2 seconds from start to gear shifting ;)
So after reading the page, I started the car on my driveway and 3 minutes later it was smog ready.
 
#21 · (Edited)
I'm going through all this crap too on my 98 S500, but to pass (go over the Not Ready State). Do this first thing on a Saturday or Sunday(When your smog shop is open). Why Sat or Sun? Because big cities like San Francisco/Los Angeles have traffic bottle-ups by mid morning to noon, and you need to have the sustained speed of over 55(without pushing the brake) for 20min then come to a stop(like you are u-turning to come back home)

The process I followed:

A) first start of the day(no moving or driving the car). On a cool day. Let it Idle for 20 minutes.

B) Make the 15min drive one way, and come back. Do it right from idle in step A. Do not press the brake while on the highway..

C) From the drive, come back to another 20 minute idle...

D) The go to the smog shop, but no turning off the engine. Hopefully your smog shop will pre-test for readiness for free-mine does...

I went through the few hundred mile drive as I thought that would cure it, but the magic occurs in first idle the drive, and the second idle.

I have the documents somewhere on this. Basically it is to weed out the evap system for the fuel tank sustained pressure.

Hope it helps,

Martin

PS.. I have done this like ten times to find a evap code, and EVAP can only be discovered this way, and in my case my M119 is not generating enough vacuum in the fuel tank due to intake manifold plenum leak of the 8 rubber rings. All the vacuum lines sensors(Gas Cap too) are all fine since the tank needs to be at a certain pressure by a certain time. My car fails to generate enough vacuum for the tank, yet not enough to really stumble the engine, so sadly I have to reset the Check Engine light which forces me to do this idle/drive/idle to see if my Check engine light will come on... The check engine for evap code will only happen for me once I'm out of the "Not Ready State", so I am an expert by now :nerd
 
#34 ·
This is picture you gave me last year for connector #1.
Connector is lifted away and ready to short but I will wait until engine gets cold because you said the air pump is to heat up the catalytic converter(?) when engine is cold. So it turns on only when engine is cold. Am I right?
Ignition position 2 and short #39 and #57, right? Extremely cautious I am now, you can see. :)
 

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#46 ·
curiosity



Yes, it has passed so far. I had some starting problem last year with Engine check light. So I replaced the fuel pump along with a lot of others.
Yes, CA requires same everywhere. Your state doesn't?
Do you have similar experience before or similar car problems before?
 
#48 ·
I was wondering how it had done in the past. Has it ever passed the functionality test? If so, what changed? If not, are Mercedes and CA just not on the same page? If not, and it is MB's problem, will CA cut you some slack (some type of exemption) since you passed the emission portion of the test.
 
#49 ·
Hey, Bob. Did your 96 SL500 get ready for test after Driver Cycle?
1)You mentioned something of "Fuel Trim" that may hinder test cycle before. Are you referring to fuel lines?
2)When handheld scanner used for "Ready", what does the scanner test first? I am asking because the first step of Drive Cycle of MB says the handheld scanner should show "test completed" with green check mark after each step is done.
In my case, the scanner does not show it completed even after the first step. Does it mean that O2 sensor went bad enough to stop further cycle?
 
#51 ·
The latest topic on Peachparts is titled "OBD II drive cycle to reset monitor flags." The first two replies are from professional Mercedes techs -- both moderators -- and one goes on to write of a '96 car: "IF the front O2 sensor is even a little weak that car might NEVER perform complete READINESS!"
 
#53 ·
o2 sensor



1) Yes, running out of all other options, I am considering to replace these. Before placing orders, I just want to see if there is any other way to verify if the sensor is out of order or not.
2) If you look thru the ALL DATA Drive Cycle by MB, you notice Step 6 (Air Injection Monitor Test) should be done with engine temperature less than 40 degree C. Here, I have a question. Is this step 6 have to be done after all previous t steps done first or I can do this with engine cold anytime? Or after previous 5 steps done and wait until engine get cold overnite and do it next day?


It feels like Today will be my last day to put any effort to work on this problem myself. So please respond asap please.
 
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