Volvo EC250 EL Theory of Operation question

I don't believe the two faults are related unless current is dropping far below what is needed to power the ECU's properly. The EBDS (electronic battery disconnect switch) is really just a big solid state relay. It can send full current or reduced current depending on the needs of the system. Diagnosing them can be a bear but I have seen the emergency stop switch under the seat cause issues before. The relays also can be and issue as well as any of the any connections in the circuit. This is one of those situations where techs break out the parts cannon to diagnose/repair the problem.

As far as the communication code that is related to the engine subnet which is communication between the ACM,ECM DEF tank armature, Nox sensors, and EGR valve. Any of these components or the harness can be at fault. But if power supply were dropping put to the ACM or ECM it could cause problems. I don't suspect this though because both ACM and ECM are reporting the code. I usually try to disconnect one component at a time while the fault is active. Whenever the code goes inactive you have found the suspect, just make sure it foes back active when you plug it back in.

Ben Witter said:

This is one of those situations where techs break out the parts cannon to diagnose/repair the problem.

Click to expand...

Thanks, Ben. I about spit beer clear across the room.

Ben, you may correct. They may not be related. I didn't mention that there were several pages of old DTC's logged. The tech who got to the machine before I was called cleared them all, since they were not active. Or not all of them anyway. Only those two returned after clearing the log. Since they did not reappear, I was of the opinion that they were immaterial to the problems at hand. No one made a list or took screen shots so whatever they were, that information is lost.

As far as the EDBS, the way I read the diagrams, it is a compound relay. There is a pull-in coil, obviously, and a set of primary contacts that make 100%, that power the starter and a few key systems. At the same time, there is a secondary output which does appear to be controlled by a solid state device, a power transistor, perhaps an IGBT. Failure of those is not unheard of but they generally handle abuse well. I'm not familiar enough with them in this application to guess the failure rate or likelihood. It could easily cause intermittent power dropouts to the supplied circuits.

Seeing that this is a battery disconnect, I've been temped to sub in a jumper for the main supply, but since that would not actually pull in the solenoid, and I don't believe trigger the transistor, the whatever sub-circuits it supplies would not be active. Pretty much decided against that. Undoubtedly it would just lead to a new set of codes that wouldn't have any real diagnostic value.

When you say that you d/c these components, do you mean while under power? I've not been to big a fan of that, myself. A few exceptions, of course, but not on sensitive components.

A parts canon is exactly what I am trying to avoid here. I find little justification for replaceology as a diagnostic technique. These parts are far too costly and at times difficult and time consuming to get. If I end up in a dealer's hands, I won't be happy if that is the approach taken. Most (but admittedly not all) problems can be found with determination, knowledge and willingness to use skill, if it's available.

I appreciate your comments Ben.

What is the def concentration? And is the sensor status green? The tank armatures are **** and the can bus runs thru them.

I have not checked it, so cant comment on it. I do believe it is green lit though.

I have a dealer tech lined up to come out next week to give me some sort of diagnosis. Ill let you guys know what turns up.

Tech met me this morning in the muck and rain. I was able to move the machine to a spot a little higher and not a swamp. He thought it odd that the EBDS was bouncing, as we all have, and connected his laptop. Found several pieces of firmware that were out of date, but was unable to do the updates because the machine power would drop out periodically. With no real, solid testing, he suggested replacing the EBDS, so I have one on the way that I'll put on tomorrow. Owner wants to eliminate it as a possible problem. His machine.

Although riveted together, curiosity made me remove the rivets and take a look at the contact surfaces, and possibly even dress them to get more life out of it. Volvo took an odd approach to the contacts. They used a flat bar that has groves in it lengthwise so that where the studs end up inside the housing, they (I believe) were flat. This would seem to lessen the contact area between the buttons and the bar. Granted, it may provide some cooling, but I've seen many heavier relays without this feature.
The studs are staked in, so no good way to removed them and perhaps put fresh faces on them, and the armature is secured in such a way that it would be difficult to remove the plate and freshen it up. All-in-all, I didn't think it worth it for what would probably be a temporary fix at best.

Hopefully I won't have to do this in a rain slicker. I was not expecting this rain. I finished one of the 3 inside jobs, and want to get my burned 460 back and planned on it next. I hope the rain does not persist, and we are forecast to have an above average hurricane season, and that usually means a wet Fall for us, even 200+ miles from the coast.

To Be continued...

OK...possible wrap on this one. Went with a new EBDS. Cleaned all the connection surfaces and sprayed some sealant over them, including the battery terminals, since I was crawling on top of them anyway. Hit the toggle, one click and away we go. Ran the machine around tossing logs for about 45 minutes and stopped and restarted it a few times. Have a reminder timer displayed for the water separator, and still have a "!" in an orange diamond up top. No idea what that means. I'll hook up our laptop and see if there are any engine codes that I can read with it.

I'll give it a few days, but unless something new pops up, looks done. Thank you all for your kind assistance!

Code turned out to be NOx sensor. Pricey little rascal. After I replace that, this machine will be 100%, until next time.

PN 22417668