V12 ECU's Reporting 'Not Ready' - Page 2 - PeachParts Mercedes-Benz Forum

MB-Dude · #16 11-12-2007, 08:40 PM

WOW… Where do I begin? Great responses.

Brett – At the time of the thumping, I was thinking ‘old school’ and wrote the post as an EGR Valve. After a response or two, it became apparent I was not calling the part correctly. Nevertheless on my SL, the canister purge valve is within inches of the Air Pump Valve for Bank 1. Hence the confusion on my part. But… with all the thumping and such, I never got an error code. Strange.

Thanks lesrrt for the information on clogged passages. I’ll check it out in the next day or so. However, I do not think my situation is vacuum related or plugged lines. The car only has ~105K on it and currently is a very clean running engine with smooth idle, fabulous acceleration, and incredible top-end with no misfiring (except for the original problem). However, that’s not to say carbon can’t build up. The issue at the moment is no apparent output from the O2 Sensor, yet the engine runs real strong. With the observations made today, the vacuum leak would have to be massive; large enough to cause very rough idle. Probably similar for a blockage.

Also Brett, another observation… disconnecting a vacuum tube on either bank causes both banks to be affected. I tested this by disconnecting something coming off Bank 2 and watched as the Bank 1 O2 Sensor was affected. Repeating this on Bank 1 side also affects Bank 1, so I know my orientation was not wrong. Therefore, any vacuum leak should cause the same symptoms to both banks. They are not independent. On the V12, there are a number of interconnecting black hoses (~1/2” diameter) that provide cross-over between the intakes; especially at the rear of the engine. Any leak on one side is felt on the other.

Nicer try John! LOL!!! As a sidebar, I didn’t have the guts to tell you that I trashed my old ’94 SL500 wiring harness back in June… just before your first post on the subject. Sorry, dude! Seriously though, I am not discounting that an ECU may be bad. Perhaps good enough for computation, but bad on verifying ‘readiness’. I may come back to you, yet!

Brett – The vacuum line goes from the Brake Booster, through a dividing wall, curves around the #12 coil, and then loops to the upper-rear of Bank 2 where it goes into a three-line connector (?), or something. This connector (if that’s what it is) feeds directly into what looks like the bottom of the intake manifold. But in fairness, I am typing this from memory and only after a very brief glance. If you want, let me know and I’ll get a picture tomorrow.

Mike – Thanks for chiming in. I’ll pop the cover off the computer box on Wednesday and see if there are any different markings on the ECU’s. Also, thanks Mike for taking a look at the data. You may something there. Tomorrow, I’ll take another, longer data capture. Please e-mail me with the parameters you recommend I capture – this will reduce the data set by eliminating stuff we aren’t interested in. ProScan lets me capture any combination of data, for any duration of time. I’ll make a multi-minute run, which will also capture a couple of the random Bank 2, Sensor 1 events.

Just to recap, looks like Brett and I have the same issue – Bank 2 Pre-Cat O2 Sensor reports zero output. This would normally imply a very lean condition. However in my case, the engine runs very smooth and strong. This suggests the ECU is receiving O2 data, computing air-fuel mixture correctly, but not reporting proper O2 status. Thus, the ECU’s are not reporting a ‘Ready’ state.

Thanks again to all. I’m starting to get into areas I have no expertise; i.e.: ECU’s, etc. Any and all input would be really, REALLY appreciated. Thanks to all.

Cheers,
Jeff

Brett San Diego · #17 11-13-2007, 01:13 AM

Quote:

Originally Posted by MB-Dude

Brett – The vacuum line goes from the Brake Booster, through a dividing wall, curves around the #12 coil, and then loops to the upper-rear of Bank 2 where it goes into a three-line connector (?), or something. This connector (if that’s what it is) feeds directly into what looks like the bottom of the intake manifold. But in fairness, I am typing this from memory and only after a very brief glance. If you want, let me know and I’ll get a picture tomorrow.

Just to recap, looks like Brett and I have the same issue – Bank 2 Pre-Cat O2 Sensor reports zero output. This would normally imply a very lean condition. However in my case, the engine runs very smooth and strong. This suggests the ECU is receiving O2 data, computing air-fuel mixture correctly, but not reporting proper O2 status. Thus, the ECU’s are not reporting a ‘Ready’ state.

Thanks again to all. I’m starting to get into areas I have no expertise; i.e.: ECU’s, etc. Any and all input would be really, REALLY appreciated. Thanks to all.

Cheers,
Jeff

Sorry, if I'm insulting your knowledge on this topic, but just to be sure. You seem to be saying that the bank 2 intake is on the left side of the V12 engine. Actually, it's the opposite. The intakes cross over the engine and feed the opposite side. So the left side intake and throttle body are the bank 1 intake and throttle, and vice versa. I just want to be certain we are always talking about the same thing.

Before I even think about ECU replacement, I'll trace the O2 sensor wiring and make sure there are no continuity issues. If you read all the diagnostic procedures in alldata (same as the MB service CD's) wiring is listed as a possible cause in pretty much every single one (not surprisingly). What I don't know is the wiring relationship between the OBDII connector, where we are reading the O2 sensor signals, and the O2 sensor itself. Does the signal go to the ECU and then get relayed from the ECU to the OBDII connector? If so, doesn't that mean it is possible that the wiring between the ECU and the O2 sensor is perfectly fine (ECU is getting a good signal.), and the problem then is simply bad wiring between the ECU and the OBDII connector? And the ultimate result is that we are getting a false bad O2 sensor reading, and we are chasing a red herring... I've got to dig up some wiring diagrams. Alldata may have them. We need to be able to read the O2 sensor signal right where it gets to the ECU.

The reason that I like this possibility is that I have no fault codes related to the bank 2 O2 sensors despite the flat pre-cat signal. I would think that fault codes would abound under those conditions.

And, finally, I checked my brake booster. The booster on my car is fed vacuum directly from the intake manifold. You are right. The line T's and goes to each side of the intake.

Brett

Brett San Diego · #18 11-13-2007, 01:44 AM

Quote:

Originally Posted by lesrrt

When I removed the intake, I noted all the small ports were all clogged with carbon. Both egr valves were also carbon contanimated too; allthe way up to were it bolts to the bottom of the intake. The flimsy metal hose that is around the back Brett, is also part of the emissions recirc sysem...I think; removed them while doing the work; they were also clogged. One thing you can ck, is the air-port plug right next to the oil fill cap. Remove it and see if you can pass a stiff wire. They are probably clogged as were mine. All these tie into the emission/adaptation curves and how the computer compensates. The long runner design will have secondary back pressure gases and will cause carbon build-up. This was a documented problem with GM's TPI engine as on one of my older Vettes. Removing these and servicing/cleaning are a test in your abilty..believe me. Now I know why someone removed the cel before I bought the car. Good luck

PS don't forget to ck the wire harnesses!!

Thanks for the heads up on clearing the passages. These fine openings are part of the PCV system, too. I just looked over it all again on alldata. The tubes running around the back of the engine from the throttle bodies are strictly PCV hoses as far as I can tell. I don't see any connection to the exhaust, just to the engine crankcase via the oil separator.

Brett

MB-Dude · #19 11-13-2007, 08:44 AM

Quote:

Originally Posted by Brett San Diego

Sorry, if I'm insulting your knowledge on this topic, but just to be sure. You seem to be saying that the bank 2 intake is on the left side of the V12 engine. Actually, it's the opposite. The intakes cross over the engine and feed the opposite side. So the left side intake and throttle body are the bank 1 intake and throttle, and vice versa. I just want to be certain we are always talking about the same thing. …

You are correct about the intakes crossing over and I am getting my Bank 1, Bank 2 intakes confused. So my descriptions are backwards. Sorry. Regardless, as far as vacuum is concerned, my observations yesterday indicate there is no separation between Bank 1 and Bank 2. What I was referring to (probably wrongly) was the physical side of the engine.

Quote:

Originally Posted by Brett San Diego

… Before I even think about ECU replacement, I'll trace the O2 sensor wiring and make sure there are no continuity issues. If you read all the diagnostic procedures in alldata (same as the MB service CD's) wiring is listed as a possible cause in pretty much every single one (not surprisingly). What I don't know is the wiring relationship between the OBDII connector, where we are reading the O2 sensor signals, and the O2 sensor itself. Does the signal go to the ECU and then get relayed from the ECU to the OBDII connector? If so, doesn't that mean it is possible that the wiring between the ECU and the O2 sensor is perfectly fine (ECU is getting a good signal.), and the problem then is simply bad wiring between the ECU and the OBDII connector? And the ultimate result is that we are getting a false bad O2 sensor reading, and we are chasing a red herring... I've got to dig up some wiring diagrams. Alldata may have them. We need to be able to read the O2 sensor signal right where it gets to the ECU. …

Must be careful here. In my case (and I think yours), the engine seems to be operating as if the air/fuel mixture is correct. At least first glance it appears the ECU’s are computing to achieve a smooth idle and strong engine performance. This suggests both pre-cat O2 Sensors are feeding information to the ECU. Although, there is the possibility that the ECU’s are running off of one O2 Sensor. Where the OBDII output comes from, I do not know. (Again, my R129 Repair DVD is unavailable so I have to rely on others.) Assuming the two ECU’s are identical and after I have a brew or two for courage, I will probably swap the ECU’s to see if the problem moves to the other bank. I do not think it will. I am leaning toward a current theory (one of many!) that whichever computer controls the ‘Ready’/’Not Ready’ signals is the culprit. I suspect that this is also the computer that generates the OBDII output. Perhaps you can research that aspect on AllData.

Later today, I will be making a long multi-minute run on the engine and capture data over that time. Mike (myarmar) has been helpful in charting the first set of data. While it was only a small data set, it was sufficient in quantity of data points to show that meaningful short-term trends could be observed.

So looks like we are approaching this problem from 2 directions – Understanding the wiring from the O2 Sensor to the OBDII connector and analyzing how the engine is computing air/fuel mixture and basic idle-running conditions.

Cheers,
Jeff

Brett San Diego · #20 11-13-2007, 10:33 AM

Quote:

Originally Posted by MB-Dude

Where the OBDII output comes from, I do not know. (Again, my R129 Repair DVD is unavailable so I have to rely on others.) Assuming the two ECU’s are identical and after I have a brew or two for courage, I will probably swap the ECU’s to see if the problem moves to the other bank. I do not think it will. I am leaning toward a current theory (one of many!) that whichever computer controls the ‘Ready’/’Not Ready’ signals is the culprit. I suspect that this is also the computer that generates the OBDII output. Perhaps you can research that aspect on AllData.

I was ruminating on the OBDII connector wiring theory again, and this probably can't be the issue. I think all the signals that we read off the OBDII connector are sent over the same pin or maybe a couple of them. If the wiring were bad to that one pin, then all the signals that you try to read would be mucked up or dead (I would think anyway). Clearly that isn't the case. Perhaps it's a problem internal to the ECU. While it may be receiving a good O2 sensor signal and processing it correctly, it's output to the diagnostic connector is screwed up for some reason.

But, I can't say anything about your issue with readiness monitors at this time. I don't seem to have that problem.

I'll try to read some more on the possibility of swapping ECU's.

Right now, I'm having fantasies of a tech on the site jumping in and saying, "I've seen this problem before... Here's what you need to do."

I think we've almost provided enough information for an armchair diagnosis.

Brett

MB-Dude · #21 11-13-2007, 10:56 AM

Quote:

Originally Posted by Brett San Diego

... Right now, I'm having fantasies of a tech on the site jumping in and saying, "I've seen this problem before... Here's what you need to do."

I think we've almost provided enough information for an armchair diagnosis. ...

Yes, if there are folks waiting for the eleventh hour... this is it! Once I gather a multi-minute scan this afternoon, I'm not sure where to go from here. I think Brett and I will entertain damned-near any ideas! There has to be someone out here who knows signal path and interaction.
Cheers,
Jeff

myarmar · #22 11-13-2007, 12:52 PM

I think you need to get a scan of the live data with the real MB scanner. The generic OBD2 probably expects to see second bank O2 sensor from the same ECU, but in case of the M120 V12 it is not the case. You maybe trying to fix something not broken.
Mike

Brett San Diego · #23 11-13-2007, 07:07 PM

Quote:

Originally Posted by myarmar

I think you need to get a scan of the live data with the real MB scanner. The generic OBD2 probably expects to see second bank O2 sensor from the same ECU, but in case of the M120 V12 it is not the case. You maybe trying to fix something not broken.
Mike

Interesting thought. For what it's worth, the function diagram of the ECU's and all their inputs and outputs shows the OBDII connector associated only with the left side ECU (bank 2). The 38-pin diagnostic connector is associated with both. Now, it's possible that is just an oversight in the diagram. But, you may be right, Mike.

Still trying to find the great section that I read on alldata last night about changing ECU's and coding them to the car, etc., etc. I want to re-read it, and I can't find the damn page again. I expected it may have insight into swapping the ECU's.

Brett

MB-Dude · #24 11-13-2007, 08:06 PM

Quote:

Originally Posted by myarmar

I think you need to get a scan of the live data with the real MB scanner. The generic OBD2 probably expects to see second bank O2 sensor from the same ECU, but in case of the M120 V12 it is not the case. You maybe trying to fix something not broken.
Mike

I agree with Brett - an interesting thought. However, my OBDII scanner does read proper variations in Bank 2 Sensor 2 (post-cat). It is independent of Bank 1 and I can vary it at will by raising engine RPM's. Therefore, it does not make sense that OBDII would exclude Bank 2 Sensor 1, but pass Bank 2 Sensor 2.

Also, I ran a 7-minute data collection run this afternoon and will post the data as I get it downloaded. BTW - my ECU's still report 'Not Ready'!

Cheers,
Jeff

myarmar · #25 11-13-2007, 11:21 PM

Quote:

Originally Posted by Brett San Diego

Interesting thought. For what it's worth, the function diagram of the ECU's and all their inputs and outputs shows the OBDII connector associated only with the left side ECU (bank 2). The 38-pin diagnostic connector is associated with both. Now, it's possible that is just an oversight in the diagram.
Brett

Brett, Jeff I believe this is not oversight. I checked ETM for 96 S600 and only N3/12 Right ECU connected directly to the OBD2 connector and Check Engine light. Probably it generates a CEL on behalf of the other ECU. It means direct OBD2 communication is only possible with Right ECU. The Left side ECU N3/11 has to send all information to N3/12 over the CAN.
Jeff this is on the scanned page I emailed you.
Mike

Brett San Diego · #26 11-14-2007, 02:01 AM

Quote:

Originally Posted by myarmar

Brett, Jeff I believe this is not oversight. I checked ETM for 96 S600 and only N3/12 Right ECU connected directly to the OBD2 connector and Check Engine light. Probably it generates a CEL on behalf of the other ECU. It means direct OBD2 communication is only possible with Right ECU. The Left side ECU N3/11 has to send all information to N3/12 over the CAN.
Jeff this is on the scanned page I emailed you.
Mike

It seems that the diagram may be incorrect, however. It clearly shows the OBDII connector associated with N3/11 not N3/12, but it is clear that N3/12 is the "master" ECU. Text in other sections on the OBDII system clearly states that fault codes are stored on and read from only the right side ECU or N3/12. So I don't know what this means for our problems, but I thought I'd say it.

Regarding not seeing bank 2 O2 sensor data correctly, I should note that I also seem to see real, changing signals from the post-cat bank 2 sensor, which seems to indicate that bank 2 sensors are read OK by our OBDII scanners.

Brett

MB-Dude · #27 11-14-2007, 11:30 AM

Yesterday, I made a 7-1/2 minute OBDII data collection run on my ’96 SL600. Data collected over this data period included:
Ignition Timing Advance for #1 Cylinder (deg)
Intake Manifold Absolute Pressure (psi)
Oxygen Sensor Output Voltage (Bank 1, Sensor 1)
Oxygen Sensor Output Voltage (Bank 1, Sensor 2)
Oxygen Sensor Output Voltage (Bank 2, Sensor 1)
Oxygen Sensor Output Voltage (Bank 2, Sensor 2)
Long Term Fuel Trim (Bank 1)
Long Term Fuel Trim (Bank 2)
Short Term Fuel Trim (Bank 1)
Short Term Fuel Trim (Bank 2)
Short Term Fuel Trim (Bank 1, Sensor 1)
Short Term Fuel Trim (Bank 1, Sensor 2)
Short Term Fuel Trim (Bank 2, Sensor 1)
Short Term Fuel Trim (Bank 2, Sensor 2)

The attached .zip file is the data formatted for east viewing, as well as a plopped into charts in MS-Excel format. The time scale for all charts is identical (7-1/2 minutes) and the same number of data points are used for each parameter. Thus, we can make direct correlation between data points on different charts.

As expected, the Long-Term Fuel Trims were stable. However, they are dramatically different:
Long Term Fuel Trim (Bank 1) = -2.34375
Long Term Fuel Trim (Bank 2) = 0.78125

I’m not sure how to explain this, or even if I should be concerned about one value positive while the other is negative.

All other data, except for the output of Bank 2, Sensor 1 Oxygen Sensor, looks normal and fluctuates as expected. You will note that the output of Bank 2, Sensor 2 Oxygen Sensor does vary the same amount as its Bank 1 counterpart.

If you look at the upper chart for Short Term Fuel Trim, it looks to me as if the Bank 2 (red line) trim follows the Bank 1 (blue line).

Thoughts from everyone?
Cheers,
Jeff

MB-Dude · #28 11-15-2007, 09:11 AM

I changed all the small diameter milky-white plastic tubing as it was getting pretty brittle. During the change-out, I came across some interesting things. Picture #1 shows one of the vacuum lines I removed – you can see oil in the line! This oil is still viscous and can move along the line. Needless to say, this should not be. As I dug deeper into this particular vacuum line, I found the line had numerous sections with oil in it. I became very encouraged as this line goes from the Bank 2 intake manifold to the Bank 2 MAP Sensor (MB p/n: 011.542.06.17).

I removed the MAP Sensor and, sure enough, there was oil inside the MAP Sensor vacuum port. Picture #2 shows where the oil was found. By now I was real excited and thought for sure that I’d found ‘the’ problem! A quick call the local dealer told me the sensors would not be available until the next day. So I decided to swap them around, in hopes the original O2 Sensor problem would move.

When I removed the MAP Sensor for Bank 1, I again made an interesting discovery – the potting mixture of the sensor had somehow become soft and deteriorated. Picture #3 shows the deformation of the potting material as compared to a ‘normal’ looking sensor. Could I have two sensors bad? At a minimum, one is definitely not good and the other may be going bad.

Over the driver’s front wheel, next to the throttle potentiometer and Body Acceleration Sensor, there is another one of these Vacuum Sensors, though I am not sure what it is used for. However, it appeared in excellent condition. So I swapped this good one with the one that had oil in it. My goal was to see if the O2 Sensor issue moved or went away.

Much to my dismay, after swapping the MAP Sensors around and replacing all the small diameter milky-white plastic tubing, there was no change in my O2 Sensor symptoms. Zero… null… nada! The engine does (subjectively-speaking) run a little smoother – especially at cold idle. But the Bank 2 O2 Sensor still reports zero output, and thus, the computers are ‘Not Ready’.

The vacuum lines needed to be changed – no question. And the Bank 2 MAP Sensor was certainly not working correctly with oil in it. I still do not know how/why the oil is in the line, but as the pictures show, it was there. And the Bank 1 MAP Sensor, with the deformed and soft potting mixture is going bad, if not already defective. So the day was not a complete loss.

But this O2 Sensor problem is getting quite quite frustrating. I am now to the point where I do not know what to do next, in terms of repairs or diagnostic work. Technical information is virtually non-existent, Mercedes is zero help and the 'latest' R129 Technical DVD (which I just received) provides no information in solving this problem. I am mentally prepared to expend the $$$ for a replacement ECU, but not as an experiment. I want to be certain an ECU replacement will solve the problem as that would be a very expensive troubleshooting item since one cannot return special order parts. Maybe it’s time to simply give up on Mercedes and cave in to what people have been telling me for years - that they're crap.

I suppose I’ll continue for a bit, but have no idea what to try next. Someone out here must have some knowledge on ‘how’ the Oxygen Sensor system ties together. I cannot believe the Mercedes repair philosophy is simply to throw parts at the problem – at the customer’s expense – hoping one of them will fix the problem. (If it is, then this certainly is not the motorcar marquee I want to be associated with.) Please, if anyone has ideas, suggestions, etc., I’d really appreciate hearing from you.

Cheers,
Jeff

MB-Dude · #29 11-15-2007, 06:24 PM

Today, I replaced the MAP Sensors for both Banks. No change in status - Bank 2, O2 Sensor 1 still reports 0v output and, of course, the ECU's are still 'Not Ready'. Both fuel systems report closed loop, but a fault with at least one O2 Sensor.

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

TheDon · #30 11-15-2007, 06:33 PM

black tape over the CEL fixes.. everything

(I wish I could be of more.. useful help)