OM603.971 EDS Codes and Diagnosis - Page 2 - PeachParts Mercedes-Benz Forum

JHZR2 · #16 02-02-2022, 09:18 PM

Quote:

Originally Posted by dieselbenz1

How does my tach work, yet I can’t measure the right resistance on the pins to diagnose code 7?

Operator error measuring signal?
You should get 150 to 300 ohms but it's a shielded signal measure ohms between the pin and ground.

Dubious it’s user error. I know how to follow the FSM and read resistance. Unless I’m not understanding the conventions on the pin numbers and color conventions (thick black vs thin black lines)????

The values are different than what you state for an OM603.971, depending upon the sensor (not sure which I have).

I don’t have the special three way diagnostic connector, so I can’t do 7.0 or 7.1. But I’ve done 7.2 thus far and not seen anything.

dieselbenz1 · #17 02-02-2022, 10:09 PM

From the bottom you can unplug the ring gear sensor and test from the connector.

wwii · #18 02-02-2022, 10:23 PM

Quote:

Originally Posted by JHZR2

I’m doing this on my 93, w140. Think it’s different?
....

The wiring diagram on my STAR DVD for a '93 W140 300SD shows the L3 sensor going straight to the EDS (N39) module and nowhere else. It shares a ground (0.75mm Brn/Grn) with the B5/1 (EDS pressure sensor) and B2/1 (VAF and IAT) sensors.

Testing for code 7:

Engine Idling N39 pin 3 to pin 20 - >3vac (rises when rpms increase)
Engine Idling N39 pin 3 to pin 25 - >2.8vac (drops when rpms increase)
(it shows those two using a breakout for the N39 connector)

Ignition OFF EDS disconnected N39 3 to 20
- 2 specs "Beru" 527 ohms +/-10%
............. "VDO" 1900 ohms +/-10%
L3 disconnected pin 1 to 2 - 2 specs "Beru" 527 ohms +/-10%
.................................................. "VDO" 1900 ohms +/-10%

N39 and L3 disconnected
... N39-20 to L3-2 < 1ohm
... N39-3 to L3-1 < 1ohm

Don't know what the Beru or VDO specs mean.

The shared ground starts at N39-3 then to a soldered splice in the engine wire harness one leg going to B2/1 the other going to the X26/2 connector then to L3-1; at L3-1 it continues to B2/1.

JHZR2 · #19 02-02-2022, 11:54 PM

Quote:

Originally Posted by dieselbenz1

From the bottom you can unplug the ring gear sensor and test from the connector.

Yeah, that’s a step I need to take, check the sensor at the connector. Could be like my alternator D+ wire, and be corroded due to failed insulation.

Quote:

Originally Posted by wwii

The wiring diagram on my STAR DVD for a '93 W140 300SD shows the L3 sensor going straight to the EDS (N39) module and nowhere else. It shares a ground (0.75mm Brn/Grn) with the B5/1 (EDS pressure sensor) and B2/1 (VAF and IAT) sensors.

Testing for code 7:

Engine Idling N39 pin 3 to pin 20 - >3vac (rises when rpms increase)
Engine Idling N39 pin 3 to pin 25 - >2.8vac (drops when rpms increase)
(it shows those two using a breakout for the N39 connector)

Ignition OFF EDS disconnected N39 3 to 20
- 2 specs "Beru" 527 ohms +/-10%
............. "VDO" 1900 ohms +/-10%
L3 disconnected pin 1 to 2 - 2 specs "Beru" 527 ohms +/-10%
.................................................. "VDO" 1900 ohms +/-10%

N39 and L3 disconnected
... N39-20 to L3-2 < 1ohm
... N39-3 to L3-1 < 1ohm

Don't know what the Beru or VDO specs mean.

The shared ground starts at N39-3 then to a soldered splice in the engine wire harness one leg going to B2/1 the other going to the X26/2 connector then to L3-1; at L3-1 it continues to B2/1.

Thanks! This helps….

I think N39/13 might go to the tachometer. Does that make sense to you. Somehow the pickup needs to get a conditioned signal to the tachometer. That’s why this is a mystery…. Tachometer works, but code says L3 doesn’t… how is that possible?

compu_85 · #20 02-03-2022, 09:59 AM

I wonder if there's a problem in the EDS module itself, like a 5v reference power supply is dead?

It's also possible one of the sensors is shorted out, dragging a reference voltage rail down?

It doesn't seem possible to me that the cluster in the tach could work, yet the EDS computer can't read engine speed.

JHZR2 · #21 02-03-2022, 10:08 AM

Quote:

Originally Posted by compu_85

I wonder if there's a problem in the EDS module itself, like a 5v reference power supply is dead?

It's also possible one of the sensors is shorted out, dragging a reference voltage rail down?

It doesn't seem possible to me that the cluster in the tach could work, yet the EDS computer can't read engine speed.

I went and probed again this am.

I must have probed the wrong pins or something yesterday.

The VDO sensor spec is 1900 +/- 10%, so 1.774kOhm is good.

That would explain why the tach works.

So now I’m maybe even more confused.

Temperature sensor works, speed sensor works.

I can’t clear the L3/speed sensor code… yet it’s coming in and feeding through to the tach.

Are there any concerns with my starting and running the car with the N39 connector/EDS unplugged? I don’t have this three way special tool that the FSM requests, but I assume that I can at least verify that we get feed power on the N39 harness, and then probe the sensor feeds themselves for voltage once reconnected…

Thoughts?

dieselbenz1 · #22 02-03-2022, 11:51 AM

Haha
Are you saying the code will not clear with the engine off.
Or does it return after you verified it was cleared?

JHZR2 · #23 02-03-2022, 12:24 PM

Quote:

Originally Posted by dieselbenz1

Haha
Are you saying the code will not clear with the engine off.
Or does it return after you verified it was cleared?

LOL, your comment earlier about user error may be right, at least with regards to L3.

I found the right resistance value per the FSM for L3 and its wiring.

I cleared the codes, put the key off for >2s, on for >10s, started the car, and after that, when I tried for codes, they were still there. I did that last night, then drove home. I wonder if some drive cycles are also needed to fully clear?

But it is more interesting than that...

I pulled the red connector at the IP. The car barely started or idled at all. Tach didnt even register unless I gave it throttle. So the RPMs were really low.

So... the EDS IS indeed doing something.

When I pulled the connector all together and ran the engine, I got battery voltage. When I loosely installed the connector, and probed each pin, I got 13.9V on one, 10.6V on the other. So 3.3V control voltage I would assume...

Per test 11 on the FSM, the value for engine idling at the ELR is supposed to be 2.5 +/- 0.5V. Its cold out, and the engine idles REALLY low with nothing attached, I wonder if maybe some base idle is set TOO low, and so the control signal is trying harder than it should to achieve something... I mean, the tach doesnt even come off the bottom, and the car idles really rough when its not connected. So maybe the EDS/ELR just cant compensate enough...

Could it be that some mechanical setting on the IP is TOO low? That would explain why when I let off the throttle, the engine speed drops for a split second below 500, before it comes back. I always thought it was just springs, but maybe its because the spring pulls the rack back to an idle that is too low, and EDS is doing everything in its power to pull it up, and just cant do enough?

Maybe thats why its throwing an engine speed code, because its too low and so it thinks its not registering right?

Thoughts??

Thanks!

dieselbenz1 · #24 02-03-2022, 12:59 PM

Easy to adjust base idle speed which should be 500 rpm if I remember correctly. The adjustment is right behind the actuator where the plug is. No need to open up the IP just remove the actuator loosen the lo k nut and adjust.

JHZR2 · #25 02-03-2022, 01:01 PM

Well, I followed up on my hypothesis, and the video by Diesel Mercedes on Youtube:

https://www.youtube.com/watch?v=MgH0fIWNcSc

I turned the 6mm screw slightly with the engine running, EDS ELR cable disconnected. Maybe 1/2 turn got me to a readable value on the tach, maybe 450. I kept turning it a bit more to get it to around 500 RPM with no EDS.

Connected EDS and it went back to 550 or a bit higher, but when I goosed the throttle and let go quick, it no longer overshot to 500 or lower, and it smoothly returned.

So my base idle was set too low, and EDS/ELR couldnt control suitably. A lesson in troubleshooting... Ill try to re-clear codes later and see what I get....

Heres to hoping that with those adjustments, Ill be able to get the AC working!!!

I know Ill still get the codes for the AFM. Do I need to care in a W140 OM603.971 if the AFM is working? Ideally Id like to disable EGR, but Im not sure if it will affect boost. My wastegate has something about aircraft on it... I wonder if it is aftermarket???

compu_85 · #26 02-03-2022, 01:58 PM

Isn't the wastegate on the .971 controlled by the EDS? And it will give you no boost if it senses that the EGR isn't working?

-J

wwii · #27 02-03-2022, 02:42 PM

Quote:

Originally Posted by compu_85

Isn't the wastegate on the .971 controlled by the EDS? And it will give you no boost if it senses that the EGR isn't working?
-J

Yep the EDS controls the wastegate via a vacuum transducer. I'm sure I've read that the EDS doesn't like it if it does not see the effect of the EGR.

JHZR2 · #28 02-03-2022, 04:03 PM

Quote:

Originally Posted by wwii

Yep the EDS controls the wastegate via a vacuum transducer. I'm sure I've read that the EDS doesn't like it if it does not see the effect of the EGR.

Yeah, so I think thats why you go to a pressure operated wastegate and then not worry. I think the idle control and boost/egr control are different...

But another thing to look into... My intake was quite clean for the age...but still want to bypass.

wwii · #29 02-04-2022, 09:15 PM

Quote:

Originally Posted by JHZR2

... I think N39/13 might go to the tachometer. ...

This is a bit late but...

I think L3 goes into N39-20 as RPM then leaves @ N39-25 as TN (unmodified RPM);
into N16-18 as TN and leaves @ N16-13 as TNA (re-formed RPM);
into A1-13 as TNA which feeds the tach (A1p5).

My tach just started acting up that's why I have been looking at this.

JHZR2 · #30 02-05-2022, 06:07 PM

Well I’m happy to say that I got to a single blink that says that all is ok.

I found that I couldn’t clear code 7 without the engine running. I guess that makes sense, it’s just not smart to wait until the engine runs next time. Resetting it with the engine running worked.

I also found that the MAF was disconnected. Not sure why it was. But it didn’t trip, at least when idling, and the codes all cleared.

I need to get a boost gauge on the car. I would assume that codes 3 and 9 with MAF would prevent boost from building?

Then again, how do I tell if I have an OE or new wastegate? Mine has a sticker on the bottom written in English to not use it on aircraft. Car drives fine, doesn’t have the rush of more power like a turbo 617 does, where it’s pretty slow so you feel it when the turbo picks up. Nor can you hear the turbo like a 617.

But it’s a 4400 lb car…

I need to find a good small gauge to plumb in.

That may be a good separate thread…