V12 ECU's Reporting 'Not Ready' - Page 3 - PeachParts Mercedes-Benz Forum

myarmar · #31 11-15-2007, 07:42 PM

Jeff, I believe there is nothing wrong with your car. As I suggested before get it scanned with MB scanner or Snap-On. Generic OBD2 scanner can get faults from both ECUs on M120, but It can't read actual values from left ECU, only values from right ECU are available to your scanner.
Regards, Mike

MB-Dude · #32 11-15-2007, 07:57 PM

Quote:

Originally Posted by myarmar

Jeff, I believe there is nothing wrong with your car. As I suggested before get it scanned with MB scanner or Snap-On. Generic OBD2 scanner can get faults from both ECUs on M120, but It can't read actual values from Left ECU, only values from right ECU are available to your scanner.
Regards, Mike

Thanks Mike for your thoughts. I do remember you mentioned this line of thinking before, and depending on how you look at this situation, you could come to that conclusion. However, I can read other Bank 2 stuff, just not the Bank 2 Oxygen Sensor. The car runs awesome and the idle is (literally) silky-smooth, suggesting engine management is on par. Yet, none of the ECU ‘Non-Continuous Tests’ get satisfied; they always come up ‘Not Ready’. And both fuel systems still report ‘CL-Fault: Closed Loop, but fault with at least one oxygen sensor’.

Nevertheless, I’ll visit the MB dealership tomorrow and see if they can squeeze me in for a CAN download. Not sure if they will fit me in (Friday, and all), but will try. Thanks again for responding and sharing your thoughts – I do consider them valid and important. Perhaps I’m just ‘too close’ to the problem at the moment.

Cheers,
Jeff

myarmar · #33 11-15-2007, 08:04 PM

From the data you've posted only single MAF, intake temp, coolant temp, etc are shown. Do you have a second set of these parameters available?
Mike

MB-Dude · #34 11-15-2007, 08:25 PM

Quote:

Originally Posted by myarmar

From the data you've posted only single MAF, intake temp, coolant temp, etc are shown. Do you have a second set of these parameters available?
Mike

Yes. Go back to Post #27, and there I attached a .zip file with both banks worth of data. The post explains what's in the file. Thanks again, Mike.
Cheers,
Jeff

myarmar · #35 11-15-2007, 08:31 PM

That's not what I mean. Do you have for example access to both MAF for left bank and MAF for Right bank?

MB-Dude · #36 11-15-2007, 09:04 PM

Quote:

Originally Posted by myarmar

That's not what I mean. Do you have for example access to both MAF for left bank and MAF for Right bank?

Doubtful. I believe the major parameters obtainable through OBDII were gathered. Again, I'll see what I can dredge up tomorrow at the dealership, assuming I can get in. I think I understand what you are looking for. And I still have the sample print-out you sent me earlier.
Cheers,
Jeff

Brett San Diego · #37 11-16-2007, 01:42 AM

Quote:

Originally Posted by MB-Dude

Question #1: The Oxygen Sensor used in this vehicle (Bosch p/n 13638) has four wires. Presumably, 2 wires are four the heater and 2 wires are for the probe. Can anyone confirm which wires are which, or point me in the right direction to find the information?

I want to begin moving along the wiring harness connection-by-connection (the word I’m think of rhymes with ‘yuck’), until I get to the ECU connector. First place to start is at the O2 Sensor itself.

Question #2: If the heater for the O2 Sensor were not to energize for whatever reason is there enough heat in the exhaust to activate the sensor?

I suspect so. However, I have been reading the Bosch Fuel Injection & Engine Management book and one of the things mentioned is that O2 Sensor output is zero if not enough heat is present. The only contradictory observation is that I have monitored both O2 Sensors when the engine is cold. OBDII reports Bank 1 at 0.5v and Bank 2 at 0.0v.

Out of desperation, I even swapped the battery with my other SL, and even the bullet-proof W123. Obviously, that was an exercise in futility.

Does ANYONE have ANY ideas? Anything? I feel I’m wasting my time documenting all this.

Cheers,
Jeff

Couple of things. If you have swapped the pre-cat O2 sensors, and the bank 2 sensor works OK on bank 1, then you already know the O2 sensor is fine. There should be plenty of exhaust heat to heat the O2 sensors to working temperature even if the heater circuit isn't doing it for some reason. But, if there was a short or open circuit in the heater, the ECU should detect it and give the fault code for it and a check engine light.

Good idea to monitor the sensor signals from cold. I should do that.

Thanks for updating this thread. I will, too, but I don't have much time to spend on it right now. I've got my high idle problem to deal with, too. I'm guessing it'll be best to solve that one first, then get back to the O2 sensor.

I'm not so sure that your flat O2 sensor signal has something to do with the lack of "readiness" indication. My diagnostics all show "complete" despite having the same bank 2 pre-cat behavior as you.

A couple of things to try: 1. Unplug the pre-cat O2 sensors one at a time while the car is running (carefully, of course) and see what happens to the signals. I did this, and the good bank 1 signal flat lined at 0.46 V. And, I'm not 100% sure at the moment, but I think the bank 2 signal did the same thing (went from flat at 0.0 V to flat at 0.46 V), which means to me that the ECU is getting a signal from the O2 sensor, and the 0.0 V signal may be real. I need to do this again to confirm and take better notes. 2. Check the temps of the bank 1 and 2 exhaust pipes with an IR thermometer and compare. Again, I can't recall exact temps, but I think bank 1 was running around 320 deg. C post cat, and bank 2 was around 60 deg cooler at around 260 deg C post cat. That struck me as a big difference, but again I need to confirm and take readings pre-cat, when I get a chance. And, I really don't know what that means at the moment, but there it is. I pinged the coolant pipes from each cylinder head at the front of the engine, and both were pretty much identical in temperature. There doesn't seem to be an issue with different head temps.

You know, the thought just struck me that maybe it is time to revisit the stuck open air injection valve theory. If there is significant air admission into the exhaust stream, there may also be the significant cooling of the exhaust gasses as I just mentioned. But, I have no idea if air admission via the injection valve could be enough air.

Brett

addendum... So I checked the O2 sensor signals before I started the car this morning. Ignition on, engine not running, hooked up OBDII reader. All sensors except bank 2 sensor 1 read flat at 0.46 volts. Bank 2 sensor 1 read 0.0 V. It appears that the ECU reports a flat reading at 0.46 V when the sensors are inactive. So I think I was incorrect when I said above that disconnecting bank 2 sensor 1 while the engine was running caused the bank 2 sensor 1 signal to go to 0.46 V. I think it stayed flat at 0.0 V, but I need to do this experiment again.

If this were a wiring problem, it seems to me that a broken wire or bad connection would be just like an inactive sensor, i.e. the ECU would report a constant value of 0.46 V as I see with the other sensors when they are disconnected or when they are not functioning because they are cold. I'm starting to swing toward the ECU outputting a bad signal to the diagnostic connector.

MB-Dude · #38 11-17-2007, 05:12 PM

After a little prodding from Mike (aka myarmar), I visited the local MB dealer today with my ’96 SL600 and explained the long version of this problem to the Service Manager. Asked him to run a diagnostic check and to print out the sensor readings so that I could further troubleshoot the problem. Received sort of a blank stare from the Service Manager as he explained that the tool they use can check individual sensors, but does not tabulate all the readings together into a nice, neat print-out. Their scanner looks deep for all faults, then using this information each individual sensor is reviewed, but only on an individual basis. From a troubleshooting Technician standpoint, makes sense, I suppose.

Anyway, he agreed to run a diagnostic check as a courtesy. (Personal note: This is when it pays to keep a good relationship with a local service group.) The result… no faults, no errors, no hiccups, no problems and all computers are showing in proper working order. His comment to me was that the engine is in excellent shape and that there is nothing for them – or me – to fix! At that moment in time, you could have pushed me over with the preverbal feather. In this regard, Mike (aka myarmar) was right – there is nothing wrong with the car and I’m chasing nothing.

So what of the computers reporting ‘Not Ready’? According to the Service Manager, model year 1996 was a transitional year for MB electronics, and some cars (fairly limited) were built with a mix-and-match of pre-OBDII vintage components and (then-current) OBDII vintage components. He theorizes that my car is one of these vehicles.

The Service Manager’s belief is that some of signals do not get properly sequenced for output through the OBDII port. Engine management is, of course, being performed flawlessly but that the ‘results’ of that management are not being properly routed to the OBDII circuitry – and will never be routed properly due to the mix-and-match of electronics. This is very similar to the line of thinking brought forward by Mike (aka myarmar). Although the OBDII port is supposed to report both banks properly from each respective bank ECU, there is a small subset of vehicles (mine is one of them) where the signals are not routed completely. Mike believes only one ECU ‘talks’ to OBDII. Apparently though, both talk to OBDII, but only one ECU is properly translated. Whatever that means. I freely admit this is a simple technical view.

So what about the vehicle’s ability to pass smog when the computers are reporting ‘Not Ready’? The Service Manager could not speak for California, but in Texas there is a check of CEL operation that allows the Smog Technician to bypass the ECU Readiness Test under certain conditions. Apparently, my vehicle would fall into this category.

Bottom line… There is nothing wrong with my vehicle! What originally caused the misfires is still a mystery and I probably will never know what caused it. The repairs outlined in this thread were needed and I do feel the engine is stronger because of those repairs, but clearly none of them were causing my ECU’s to report ‘Not Ready’.

I want to thank everyone who contributed to this thread for your insight, knowledge, suggestions and morale support. Especially Mike who gave me a number of ideas and was the one who came forward with the thinking that there is nothing wrong. (Talk about courage in the face of opposition!) If I hadn’t visited the dealer this morning, I’d still be chasing a ‘ghost’.

Cheers,
Jeff

PS: Just checked the vehicle and OBDII reports the same information as shown in the attachment of post #1.

myarmar · #39 11-19-2007, 07:05 PM

I'm glad you sorted it out. There was a risk fixing it to death and spending a lot of cash for ECUs. Now as you saved all this $$$ buy a real scanner. With all your MBs it will pay for itself in no time.
WBR, Mike

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