S-Prihadi

A new member has issue with his OM651 diesel engine on a 2013 facelift W212.
He asked and we discussed it in this thread of mine, post no #10 https://mbworld.org/forums/e-class-w...ml#post8909418

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When he turned the key to CRANK and let go, the car started about 50-55 seconds later.

EDITED 23rd Jan 2024. What a rude member . He deleted his video !!!!! And I been helping him and solved the issue which is Relay R. We need the video for case study !!!

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It got me thinking, since this can be dangerous if another person hands are still at/on the engine troubleshooting or whatnot within and after the 50 ish seconds delay.

So I looked up the START FUNCTION, for his OM651 and our M276.
I am attaching the documents.


OM651


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M276




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Basically MB uses the same operational logic between the OM651 and M276....supposedly it is so, as written in WIS......for ENGINE STARTING sequence and readiness check, perhaps a slight difference only
because of the diesel OM651 has glowplug/heater and the OM651 in discussion was at 12.0C cool temperature as per his video.

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Now I decided to do a quick test, to simulate that Relay M can activate its coil, but mechanically can not pull down and closed its contact point and sending power to starter motor solenoid.
I want to know, how long the ECM will do engine "CRANKING" if starter motor never actually spin , but the bogus/dummy Relay M is seen as electrically active by ECM.
I remove the green starter Relay M and replaced it with a DMM and a 120 milliamps test light as a dummy load in lieu of the green starter Relay M.
I want to know how smart or dumb the ECM MED177 on M276 engine is, when I do this test.



I done 2 tests :
Test 1A and 1B, Crank the engine like normal where the CRANK position is a simple 1 second CW rotation of the key.
Test 2, Crank the engine with HOLDing the crank position for 40 seconds.
Our M276 engine is not the oldie traditional analog starting system, even with the key inserted into the ignition slot, our engine is basically a PUSH BUTTON start,
the touch start, aka the electronic start. The computers are the one deciding if it will start/crank your engine or NOT.
We beg for it to start ....by us : using the key FOB or push-start-button... that is all we can do , the go ahead is up to those 4-5 theft relevant modules/computers which protect/operate our car.

The test 1 and test 2 video below:


Is there any DTC when I use the test light as dummy load to replace the green starter Relay M....nope.
Is there any DTC when I un-plug green starter Relay M ...... Yes. The ECM sees that there is no electrical load, it declare open circuit DTC P061513




If the Relay M say is shorted, will DTC be produced by ECM ? Most likely, but I DARE NOT TRY that .
Usually short circuit DTC for a component always exist at modules because devices are powered not by oldie mechanical switch but thru driver circuits.


The wiring route as follows :
N276.9 or M276.8, ECM Connector F pin 57 is a ground (-) signal to and for Relay M coil (85/86) at Front SAM, so from ECM to Front SAM for relay's M coil (85/86) activation only, aka control.
Relay M power (30) for its load to starter solenoid is from fuse 7 at Front SAM. Relay M output (87) goes to starter solenoid M1, The CRANK is called Circuit 50.
Relay M power (+) for its coil (85/86 ) is from Circuit 87M circuit which is rather a long story of its routing and involving ECM and other relay too. Very time consuming to really see the total interconnection start to end.




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So, how do we troubleshoot the delay to CRANK issue of the OM651 in this case study , when and if it happen to our engine too ?

01. We must first find out, if the delay is command caused or mechanical caused ?
From the test video I posted, it is clear that Xentry indication of Circuit 50 ( relay M ) being commanded and the actual electrical power to Relay M coil is not in sync 100%, but the ECM does
activate the coil's (85/86) of Relay M at like 0.3 seconds delay and will kill power within 3 seconds if other X,y,Z parameters not satisfied,,,like engine never actually spin the starter and hence no crankshaft RPM signal.
A test light and a DMM-voltmeter is a must use, can not avoid it. Scanner like Xentry or good equivalent is a must have too.
The DMM is to confirm that there is or not a very low voltage feed to relay's coil and if current supply is enough to drive a 120milliamps test light. Basically "bad" contact/wiring test.
The relay itself consumes only 1.9 watts or approx 160 milliamps , hence the test light is a safe load to not damage the ECM and good enough to confirm enough amperage to activate Relay M.

02. If the delay is command caused, the test light and DMM will only be ON and show proper voltage when the delay has expired.

03. If 02 is not the case, and test light + DMM shows no delay in its activation, it then must be the relay mechanical link which get delayed pull down by the coil.
The coil can when cold perform bad and not able to pull down the mechanical link to actually make a closed circuit.
I have assisted another member here with the same COLD delaying his relay , but the relay was Relay R, which is the power source of tranny computer, so he immediately got DTC there then and engine wont start.
https://mbworld.org/forums/e-class-w...ation-tcm.html

Starter Motor M1 solenoid has no supporting circuit at the starter itself which can produce DTC, unlike tranny computer in the case of Relay R.
The ECM when powering Relay M to CRANK can only tell if the relay's coil 85/86 is open circuit or shorted/short-circuit, that is all it can detect.

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The significant difference between our gasoline vs the OM651 diesel engine is that we do not use glowplug heater.
In OM651 the glowplug heater has a controller module called N14/3, which uses LIN to communicate with diesel engine ECM N3/9.
I read the glowplug protocol WIS, it will not cause engine CRANK delay.


The problems of the owner of OM651 also getting lots of lost communication to many modules, that is a 2nd issue separate to the suspected relay M and not the topic of this
thread.

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So, I guess the MED177 and whatever the ECM type OM651 uses, is probably not a 100% similar in the START FUNCTION coding/program/algo.

At least I feel safer now when and if Relay M mechanical link goes bad or slow on my M276.8
I do initially worry with the statement in the WIS stating : UP TO 40 seconds cranking allowance by the "touch start" aka CRANK signal of our key or push button start.

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S-Prihadi

I have to add.
I have also waited for 120 seconds after doing CRANK and kept Ignition ON, just in case there is a 2nd ECM controlled CRANK event like a re-try.
Nope, the ECM did not do such a thing as 2nd try on its own.

S-Prihadi

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So, the real issue was Relay R. Post #32 of my thread : https://mbworld.org/forums/e-class-w...ml#post8910953

Now I have to test such failure on my car.

THE SIMULATION : Let's do relay R being energized but its contact point failed to close.
So basically the Tranny did not get power because Tranny computer get power from Relay R.
It does not make sense to me that the OM651 can have a delay if this Relay R is totally not closing its contact point, as when a ready status is not coming out of tranny computer,
engine will never be able to be allowed start/CRANK .

Probably this Relay is not totally open for its contact point, but a bad/worn contact point and causing very very low voltage, as such tranny is intermittently ON-OFF-ON and
hence the delay. However still it does not make sense though..... if based on my ECM, the command to crank Circuit 50 has a time out feature for safety.
The ECM will not authorize 2nd time automatic cranking if driver does not do the actual CRANK or command for the 2nd time.
Time out is time out, if for my ECM MED177 of M276.820 3.0 Turbo.

The test set up.






Relay R gets the real relay R , but its Pin 30 (3) and Pin 87 (5) is not connected.
Pin 30 (3) is +12V POWER INPUT and Pin 87 (5) is +12V POWER OUTPUT.




Relay M which is CRANK ( Circuit 50 ) to starter solenoid is being replaced by a test light as dummy load and a DMM to see voltage, same test set up like 1st test a few days back, for Relay M.


When tested, there was totally no CRANK happening at Relay M, with Relay R not supplying power to Tranny Computer Y3/8n4.




So, either OM651 computer is different in protocol to MED177 ( I believe this is the case ), or there is/are other intermittent and hidden issues with that car/OM651 we do not know yet.
When the owner of the OM651 borrowed the horn relay which is the same as Relay R, his car resume back to normal CRANK with no delays.

Again, my effort is to test with our M276 because I do not want such dangerous delay to CRANK happening, if Relay R is bad.
For the time being we MED177 ECM owners are safe


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Relay DIN standard pin out and legend


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