'05 CDI "communication fault" N14/2 Glow Output Stage 2538-4 jay-bob? - PeachParts Mercedes-Benz Forum

ROLLGUY · #1 12-19-2022, 08:01 PM

I have a current code 2538-4 communication fault Glow Output Stage. I also have a few stored codes that my MB II will not erase because of a communication fault. Can I assume both are caused by the same thing? There are other modules that I access and can clear codes just fine, but the engine module is not letting my MB II communicate. My STAR computer is not working now, so the MB II is all I have. How about it jay-bob, you got any ideas?

jay_bob · #2 12-20-2022, 02:16 PM

On the 648 (and 642) the Glow Plug Relay talks to the ECU on LIN bus (single wire slow speed serial) and shares that line with the voltage regulator.

This is the routing of the data wire from the ECU to the glow plug relay and alternator.
All of these are 0.75 mm (or about 18 gauge American) solid blue according to my Star Finder

Pin 66 on the ECU, goes out to a Splice Z26/1, in the harness near the EGR valve
Branches to Pin 1 on the alternator regulator connector and Pin 12 on the N14/2 glow plug relay

On the GP relay multi wire connector
pin 1 cylinder 1 2.5 mm (similar to American #14) black/blue
pin 2 cylinder 2 2.5 mm black/violet
pin 3 cylinder 3 2.5 mm black/red
pin 4 cylinder 4 2.5 mm black/yellow
pin 5 circuit 87 (protected engine management logic power) 0.5 mm (#20) red
pin 6 circuit 31 0.5 mm brown
pin 7 cylinder 5 2.5 mm black/green
pin 8 cylinder 6 2..5 mm black/white
pin 9 , 10, 11, no connection
pin 12 LIN bus 0.75 mm blue

The big connector with single wire on the GP relay is circuit 30, straight battery feed, via a 10 mm (or about 6 gauge American) via fuse 69, 125 Amps, in F32 (the 'front prefuse' box in the passenger foot well behind the shielding plate).

ROLLGUY · #3 12-20-2022, 04:32 PM

Thank you! I just replaced the alternator, so could that be the problem? The car did not have this issue before the alternator was changed. The car had a parasitic draw, and that was the last thing that could be the culprit after all the other systems were ruled out by millivolt test on fuses. Turns out, that was the problem.

jay_bob · #4 12-20-2022, 06:01 PM

Well I did have an issue with a NAPA replacement alternator having a dead LIN bus chip in it. Maybe the alternator regulator is sucking down the LIN bus...

ROLLGUY · #5 12-20-2022, 07:31 PM

Quote:

Originally Posted by jay_bob

Well I did have an issue with a NAPA replacement alternator having a dead LIN bus chip in it. Maybe the alternator regulator is sucking down the LIN bus...

I got a Genuine Bosch rebuild from my Euro parts source (S&J Euro Parts). It came in a new Bosch carton, and looked new.

About an hour ago, I removed everything so I could get to the alternator to check the plug. It all looked good, with everything connected properly. I scanned for codes again, and got the same message when checking "CDI 3 Common Rail Diesel Injection 3" I got- "Fault in communication with ECU"
I tried clearing codes in other modules, and they cleared just fine (mostly under voltage codes). I believe this is all related, but have no idea how to fix it.

EDIT: Also, the alternator is charging at 14.6 volts +-

TimFreeh · #6 12-21-2022, 04:28 PM

Quote:

Originally Posted by ROLLGUY

...... I scanned for codes again, and got the same message when checking "CDI 3 Common Rail Diesel Injection 3" I got- "Fault in communication with ECU"
I tried clearing codes in other modules, and they cleared just fine (mostly under voltage codes). I believe this is all related, but have no idea how to fix it.

EDIT: Also, the alternator is charging at 14.6 volts +-

The 'fault in communication with the ECU' error code isn't the same thing as the first error code saying the ECU couldn't communicate with the Glow Plug controller.

The 'fault in communication with the ECU' error is telling you your scan tool can't seem to interface/find the N3/9 main CDI control unit.

Was the ignition on when you scanned for codes? If not the scan-tool won't find the N3/9 module because it isn't powered up.

ROLLGUY · #7 12-21-2022, 04:38 PM

Quote:

Originally Posted by TimFreeh

The 'fault in communication with the ECU' error code isn't the same thing as the first error code saying the ECU couldn't communicate with the Glow Plug controller.

The 'fault in communication with the ECU' error is telling you your scan tool can't seem to interface/find the N3/9 main CDI control unit.

Was the ignition on when you scanned for codes? If not the scan-tool won't find the N3/9 module because it isn't powered up.

Yes the key was on, as I was able to clear codes in other modules. I was also able to see six faults in the CDI module, I just was not able to clear the codes. Four were stored, the other two were the glow plug controller (currant and stored). I know they are two different faults, but I can only assume they are caused by the same thing, as they both showed up after I changed the alternator. Could there be a fuse that is blown? Since the scan tool worked to clear codes in other modules, I assume at least the diagnostic circuit/fuse is good.

TimFreeh · #8 12-22-2022, 10:28 AM

Quote:

Originally Posted by ROLLGUY

Yes the key was on, as I was able to clear codes in other modules. I was also able to see six faults in the CDI module, I just was not able to clear the codes. Four were stored, the other two were the glow plug controller (currant and stored). I know they are two different faults, but I can only assume they are caused by the same thing, as they both showed up after I changed the alternator. Could there be a fuse that is blown? Since the scan tool worked to clear codes in other modules, I assume at least the diagnostic circuit/fuse is good.

I'm confused.

In your first sentence above you indicated you were able to see 6 codes and erase 4 - this indicates at that time your scan tool was able to see/communicate with the N3/9 CDI main control unit. As I recall the glow-plug output stage error is from the CDI control unit?

However your screen shots in post #5, after you disassembled things to verify that the plug to the alternator was all good, indicates your scan tool can no longer see/communicate with the N3/9 control unit. So at this time you can't see any codes until you can get your scan tool back into communicating with N3/9.

If the car starts and runs you have power to the CDI control unit. If the CAN wiring to N3/9 is good your scan tool you should be able to communicate with N3/9. You have to get the communication working before you can really continue.

Given the LIN bus is apparently shared with the Glow plug output state and the alternator, and the error appeared immediately after alternator replacement, it seems kind of likely that the new alternator doesn't understand its supposed to communicate with a LIN bus and has done something to take down the bus.

As Jay-bob said in his post he and others have replaced alternators with NAPA sourced remans and had issues. I realize your Bosch alternator should be of higher quality but I'd bet there are a couple of different versions of that alternator that share the same basic case and maybe you didn't get the version that is LIN capable?

You need to figure out why your scan tool isn't able to communicate with N3/9 - I don't think that problem has anything to do with the new alternator or the LIN bus. If you can get N3/9 back into communication I'd disconnect the plug to the alternator, which would isolate that LIN bus connection, and see if that brought the LIN bus back on-line which should erase the Glow-plug output state error in the CDI control unit.

ROLLGUY · #9 12-22-2022, 10:58 AM

Quote:

Originally Posted by TimFreeh

I'm confused.

In your first sentence above you indicated you were able to see 6 codes and erase 4 - this indicates at that time your scan tool was able to see/communicate with the N3/9 CDI main control unit. As I recall the glow-plug output stage error is from the CDI control unit?

However your screen shots in post #5, after you disassembled things to verify that the plug to the alternator was all good, indicates your scan tool can no longer see/communicate with the N3/9 control unit. So at this time you can't see any codes until you can get your scan tool back into communicating with N3/9.

If the car starts and runs you have power to the CDI control unit. If the CAN wiring to N3/9 is good your scan tool you should be able to communicate with N3/9. You have to get the communication working before you can really continue.

Given the LIN bus is apparently shared with the Glow plug output state and the alternator, and the error appeared immediately after alternator replacement, it seems kind of likely that the new alternator doesn't understand its supposed to communicate with a LIN bus and has done something to take down the bus.

As Jay-bob said in his post he and others have replaced alternators with NAPA sourced remans and had issues. I realize your Bosch alternator should be of higher quality but I'd bet there are a couple of different versions of that alternator that share the same basic case and maybe you didn't get the version that is LIN capable?

You need to figure out why your scan tool isn't able to communicate with N3/9 - I don't think that problem has anything to do with the new alternator or the LIN bus. If you can get N3/9 back into communication I'd disconnect the plug to the alternator, which would isolate that LIN bus connection, and see if that brought the LIN bus back on-line which should erase the Glow-plug output state error in the CDI control unit.

Thank you Tim for the great information!

"In your first sentence above you indicated you were able to see 6 codes and erase 4 - this indicates at that time your scan tool was able to see/communicate with the N3/9 CDI main control unit. As I recall the glow-plug output stage error is from the CDI control unit?"

I was not able to erase any codes in the CDI control unit, I only get the "fault Communication with ECU". Yes the glow-plug output stage error is from the CDI control unit. It had 2 codes that were stored and current. The other 4 were stored. My scan tool is able to communicate with all the modules, and will read and clear all codes except for the CDI module, it will not clear codes. That is the part that is baffling me. The car starts and runs, battery charging at 14.6 volts, but has a CEL and glow plug light on constantly.

ah-kay · #10 12-22-2022, 11:23 AM

Have you tried to change out the GP controller to eliminate hardware issue first?

TimFreeh · #11 12-22-2022, 12:34 PM

Quote:

Originally Posted by ROLLGUY

Thank you Tim for the great information!

"In your first sentence above you indicated you were able to see 6 codes and erase 4 - this indicates at that time your scan tool was able to see/communicate with the N3/9 CDI main control unit. As I recall the glow-plug output stage error is from the CDI control unit?"

I was not able to erase any codes in the CDI control unit, I only get the "fault Communication with ECU". Yes the glow-plug output stage error is from the CDI control unit. It had 2 codes that were stored and current. The other 4 were stored. My scan tool is able to communicate with all the modules, and will read and clear all codes except for the CDI module, it will not clear codes. That is the part that is baffling me. The car starts and runs, battery charging at 14.6 volts, but has a CEL and glow plug light on constantly.

I still don't think I'm getting my point across.... Let's try it this way.

Right now, today at this moment can you communicate with the CDI control module N3/9? Can you get a menu that shows you options to take to read codes or look at live data in the N3/9 module?

I have a couple of aftermarket scan tools that I use as a backup to my SDS system, its not at all uncommon for those tools to not communicate with some of the control modules in the car. I've also seen them communicate with a module on one day and not communicate on another day.

jay_bob · #12 12-23-2022, 07:07 AM

Remember that the path for communication to the ECU goes like this:

OBDII port -> ZGW (Central Gateway) -> Engine CAN bus -> N3/9 ECU

And from the ECU to the N14/2 Glow Plug it is a LIN bus that leaves the N3/9 ECU and goes to the N14/2 Glow Plug and the G1 Alternator regulator.

So we have 2 things that have to work.
First the scan tool has to see N3/9 through the central gateway via the Engine CAN bus.
Then assuming it can see N3/9 and communicate with it, then the LIN bus has to be operating for the N3/9 to communicate with N14/2.

You can't directly talk to N14/2 with the scan tool, you can only get get N14/2's status as N3/9 has determined.

So if the LIN bus is down then you're not going to see the N14/2.

Another thing to try: get in, close the door, put key on position 1 (just the radio on).
Navigate to the MPH display on the cluster.
Push in the dimmer knob 3 times rapidly, you should see Ub = 12.xx V
Start the car and watch the voltage. If it immediately goes to 14.x V then the regulator is not communicating and it's in default (make nominal voltage all the time) mode.
If the voltage walks up from 12.xx to 14.xx over the span of about 15 seconds then it is getting orders from N3/9 to walk the load in. Meaning the LIN bus is working.

dieselbenz1 · #13 12-23-2022, 08:22 AM

The regulator part should be
Mercedes PN: 0031549706
Bosch PN: F00M145225
Others cause lin faults

ROLLGUY · #14 12-23-2022, 09:20 AM

I'll say it again, you guys (jay_bob, TimFreeh,dieselbenz1) are awesome! Thanks for the great information!

Quote:

Another thing to try: get in, close the door, put key on position 1 (just the radio on).
Navigate to the MPH display on the cluster.
Push in the dimmer knob 3 times rapidly, you should see Ub = 12.xx V
Start the car and watch the voltage. If it immediately goes to 14.x V then the regulator is not communicating and it's in default (make nominal voltage all the time) mode.
If the voltage walks up from 12.xx to 14.xx over the span of about 15 seconds then it is getting orders from N3/9 to walk the load in. Meaning the LIN bus is working

I will try this today. I just put a brand new AGM battery in the car, and tested the charging system. I get about 14.6 volts with my probes directly on the battery with the engine idling. Yes that tells me that the alt is charging, but it may be in default mode as you say. Again, VERY GOOD information!

ROLLGUY · #15 12-23-2022, 09:25 AM

Quote:

Originally Posted by ah-kay

Have you tried to change out the GP controller to eliminate hardware issue first?

Yes, that is the first thing I did, and it changed nothing. I now have a new glow plug control in stock! (a good thing, as we have four cars that it fits between my brother's family and I).