LML service bulletin

[Chevy1925]

Your LMM nox sensor won’t work right to test. Funny enough, there is like 3 or 4 different nox 1 sensors for LML’s. We keep one of each on the shelf.

Are you sure the 9th injector is working? What’s the soot load? Does the truck blow any smoke?

You might try a forced regen to see if it will actually do it. If it won’t, let us know the reason it kicked out of doing it.

 

[2004LB7]

No smoke. Pipe is clean.

I remember a year or two ago he replaced the Nox sensors and we had to use the Autel to run the reductant quality test to clear it. Hasn't given him any trouble since. When he replaced the heater, he pull the def injector and he said it looked perfect and no deposits or crystalization. I don't remember if he looked at the 9th injector.

Soot load was 37 grams last I checked. I don't know what the ash load is. He is thinking of bringing it over so I can run a service regeneration. I told him to wait for some replies to the forum first.

He also sent be a text recently saying he just went ahead and replaced the dpf pressure sensor. If he brings it over I can check if the readings are any different then before

 

[Chevy1925]

Find out if he put a factory sensor in or not. The aftermarket is junk for aftertreatment sensors.

Basically, something is not jiving between the last regen, how much fuel it has used since then, and the readings it’s seeing. It might be regenning right away after a regen, that’s part of how that code sets.

You might need to smoke test the intake and exhaust. LML is very sensitive to intake leaks. Leaks at the turbo horn or even at the maf its self will make these things throw all kinds of weird codes yet no maf code. If the exhaust has a leak and egt’s are not reading right, it will cause this issue too.

 

[2004LB7]

Ok. Thanks

I'm pretty sure all the sensors he's purchased where aftermarket

 

[2004LB7]

Another question. On the DPF pressure sensor, does there need to be any programming for it to work correctly? My uncle said he read the pressure offset needs to be programmed in for it to work.

 

[Chevy1925]

Never had to do one but I’ll look it up

 

[Chevy1925]

Since you are at 37 grams, that might have been the issue. Needed a forced regen

 

[2004LB7]

Ok. So it looks like a forced regen is the procedure after replacing the pressure sensor.

I thought they would do an active regen at about 42 grams. Or based on miles or hours. Maybe he's hit the miles or hours and didn't let it complete fully a few times?

 

[Chevy1925]

You gotta clear the code and force the regen or it won’t do anything on its own.

You literally gotta hold the damn aftertreatments hand to make everything work again if it had an issue. It’s f-ing retarded… hence the fact you had to trigger the heaters. dodge and Chevy are the hardest to figure out as far as what kind of hand holding they need to be fixed and back working. Ford seems to have a better grasp at it.

Either way, it’s tedious and f-ing dumb.



Have I mentioned it’s dumb?

 

[2004LB7]

Crap. So, are you saying the P2459 code will prevent a service regen from starting?

If I clear it, it will reset all the monitors too. Then he's back to driving it for another few hundred+ miles to try and get the readiness monitors set. Seems like we would be starting all over

 

[Chevy1925]

Crap. So, are you saying the P2459 code will prevent a service regen from starting?

If I clear it, it will reset all the monitors too. Then he's back to driving it for another few hundred+ miles to try and get the readiness monitors set. Seems like we would be starting all over

Can’t say for sure. GM isn’t clear on it but like in that pic, it states if you are over that gram amount, you gotta clear the code and force a regen. That’s kinda their hidden way of saying it’s not going to regen without doing so.

But yeah, you are going to have to reset the monitors after

 

[2004LB7]

Update. So my uncle too the truck to my relative who has the Autel again. They ran the service regen. Said it completed ok

Then mentioned the code remains. I told him he should clear it first then run a service regen. He said he tried to clear it but it wouldn't clear

So...????

I think the next step it to command a regular regen. But not sure

 

[Chevy1925]

That or his new sensor isn’t jiving

 

[2004LB7]

I'll need to ask again what sensor he has in it. He mentioned wanting to put the old one back in as he didn't really believe it was bad

 

[2004LB7]

Didn't get to do too much yet. Hooked up my V2 with the laptop. Didn't see any codes??? Just shows a blank white screen on the OBD code check tab?????. Not sure what's up. Even ran the latest update to make sure and still no difference

But I did monitor the voltage pid for the differential pressure sensor, both new and old ones. Used a hand pump to pull a vacuum on the downstream sensor line. Voltage was smoothly rising. From .1 to 4.1 volts with about 22 inch of vacuum. Both sensors read the same. Also the 4 EGT sensors seemed to be ok. Hard to tell completely as it was only during idle.

And EGR was commanding 20% and actual was 20%. Didn't take it for a drive to see if anything was different here.

Lastly, after trying to clear any codes, even though it didn't show any, I used the DVT to command the forced regen for the next drive cycle. Then looked at the DPF regen pids and inhibit was idle speed, which makes sense, and regen reason was "external request" which I take as the DVT forced regen command worked.

We didn't have a lot of time and he was going to head on a road trip up to reno so plenty.of time for the system to do it's regen and for some or all of the monitors to set. I will have to check it again when he's back

 

[snowman22]

Slightly different issue, but I had an EGR issue with my LML. After fixing the issue it took 1,100 miles for the monitors to set to meet the new CA rules.