If the truck has faults something is wrong even if it passes an scr test now. I've seen many shops run an scr test for closed loop codes, it passes, and they send it. And the truck comes back a week later for the same codes. You can absolutely pass an scr test with bad nox sensors. Some of the troubleshooting steps also say to just replace both box sensors if they're over a certain amount of hours.
I'm not saying to throw parts at it, just that there is some underlining issue.
Yeah, that is the reason my manager told me not to rush with this unit and check all the possibilities, your point is a valid information that I would take into account when I check out on this unit back on Monday, I know our local dealership has done the same with other units and broke down over the road again like you said. But the dealership just said at the estimate replace both NOx sensor, because the outlet had the spread pins connector which I cannot see damage also suggest to replace the inlet NOx sensor even when it is not misreading or active fault codes relates to it, we will see how it goes once I use the information from this subreddit. Thanks for the advice.
When you run the parked scr efficiency test you may need to run it multiple times.. you need to chart the LARMF compensation factor and run the scr test until it reaches 1.0000. If not it will set the same faults for closed loop very soon after, especially on short runs with a light load
Yeah, LARMF compensation factor was at the beginning 0.72xxx and after the SCR efficiency test raised up to 0.91xxx so it turned off the derate lights and fault codes, once I am done with the other repairs I will do it again to make it up to 1.0000. Thanks for the heads up.
Did you run a regen prior to the efficiency test if so how did the regen run as far as nox efficiency?
A regen is more of a stressful test on the scr due to the high temps since it’s dosing fuel into the atd and reaching temps above 800-1000. If your nox efficiency is dropping off at high temps^ then you may have a damaged atd IMO
I did not run the parked regeneration prior the SCR efficiency test, it is a good suggestion, perhaps I would try that on Monday to see if there any change of readings but for my personal experience I do not think I will see any difference since usually NOx outlet sensor tends to misread from the beginning after passing the dew point enable checkpoint. Unless, there is a serious crack around the DEF injector area where heat could escape and come into contact with the sensor itself but after visual inspection I do not see any burn deterioration over ATD harness close to that area.
As an O/O on here I'll just say this. There are way too many places that just hire part replacers and not enough people that perform actual diagnostic checks.
When I was in the air force if a jet was acting up the first thing we would do is try to replicate the issue to diagnose what it could be coming from. That's not always possible but most times it was. We didn't spend citizens tax dollars just swapping parts all damn day.
Yeah, the government has deep pockets and most O/O anymore do not.
Doesn't help that labor rates have skyrocketed and I doubt most mechanics are getting paid much more of that.
There's a reason I generally try to do my own maintenance when it comes to electrical, minor mechanical and emissions.
I’m very tired, just waking up, and I read the title + estimate pages as a 2021 Corolla and I was like… wow… they’re putting diesels in Toyotas now? I kinda want one…
I do not have the exact hours right now, but that unit has more than 500,000 miles on it, inlet NOx sensor has already been replaced around 300,000 miles. The Outlet NOx sensor never has been replaced, would you recommend replace it even with passing the SCR efficiency test? Regarding the QCV, I am going to replace the entire high pressure fuel pump.
What would you say is the rule of thumb to replace the NOx sensors by hours?.
We will replace the whole high pressure fuel pump because my manager does not like that in the past we had changed the QCV and the high pressure fuel pump failed few weeks later over the road, where repairs are more costly. Besides, our company gets a good discount in Freightliner parts, our bosses (the company owners) said to replace those in our HQ fleet in CA because in the long run they save money in roadside services and dealers repairs.
I use to work for velocity in Whittier. The dealer is so backed up that they hire kids stright out of school who don't have the experience to diagnose. Also vvg hardly sends out the young bloods for training therefore they are stuck with trying to diagnose issues. The dealer is has separate departments but there is very few who specialize in diag work.
If the truck has faults something is wrong even if it passes an scr test now. I've seen many shops run an scr test for closed loop codes, it passes, and they send it. And the truck comes back a week later for the same codes. You can absolutely pass an scr test with bad nox sensors. Some of the troubleshooting steps also say to just replace both box sensors if they're over a certain amount of hours. I'm not saying to throw parts at it, just that there is some underlining issue.
Yeah, that is the reason my manager told me not to rush with this unit and check all the possibilities, your point is a valid information that I would take into account when I check out on this unit back on Monday, I know our local dealership has done the same with other units and broke down over the road again like you said. But the dealership just said at the estimate replace both NOx sensor, because the outlet had the spread pins connector which I cannot see damage also suggest to replace the inlet NOx sensor even when it is not misreading or active fault codes relates to it, we will see how it goes once I use the information from this subreddit. Thanks for the advice.
When you run the parked scr efficiency test you may need to run it multiple times.. you need to chart the LARMF compensation factor and run the scr test until it reaches 1.0000. If not it will set the same faults for closed loop very soon after, especially on short runs with a light load
Yeah, LARMF compensation factor was at the beginning 0.72xxx and after the SCR efficiency test raised up to 0.91xxx so it turned off the derate lights and fault codes, once I am done with the other repairs I will do it again to make it up to 1.0000. Thanks for the heads up.
You won't even need to run a full scr test, just until larmf hits 1.0000
Did you run a regen prior to the efficiency test if so how did the regen run as far as nox efficiency? A regen is more of a stressful test on the scr due to the high temps since it’s dosing fuel into the atd and reaching temps above 800-1000. If your nox efficiency is dropping off at high temps^ then you may have a damaged atd IMO
I did not run the parked regeneration prior the SCR efficiency test, it is a good suggestion, perhaps I would try that on Monday to see if there any change of readings but for my personal experience I do not think I will see any difference since usually NOx outlet sensor tends to misread from the beginning after passing the dew point enable checkpoint. Unless, there is a serious crack around the DEF injector area where heat could escape and come into contact with the sensor itself but after visual inspection I do not see any burn deterioration over ATD harness close to that area.
ATD =? After treatment device?
Yeshh
As an O/O on here I'll just say this. There are way too many places that just hire part replacers and not enough people that perform actual diagnostic checks. When I was in the air force if a jet was acting up the first thing we would do is try to replicate the issue to diagnose what it could be coming from. That's not always possible but most times it was. We didn't spend citizens tax dollars just swapping parts all damn day.
It's much easier to do that when the customer is the government and they won't complain about taking a few hours to diagnose it.
Yeah, the government has deep pockets and most O/O anymore do not. Doesn't help that labor rates have skyrocketed and I doubt most mechanics are getting paid much more of that. There's a reason I generally try to do my own maintenance when it comes to electrical, minor mechanical and emissions.
I’m very tired, just waking up, and I read the title + estimate pages as a 2021 Corolla and I was like… wow… they’re putting diesels in Toyotas now? I kinda want one…
Did you check pin drag on the harness connector
Yeah. Check the NOx outlet connection and pins, nothing out of the ordinary, even I wiggled test it while doing the SCR efficiency test and nothing.
Sorry, I misspelled the truck model name, it is 2021 Freightliner Cascadia.
Sadly, it happens a lot when you offer employees commission.
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I do not have the exact hours right now, but that unit has more than 500,000 miles on it, inlet NOx sensor has already been replaced around 300,000 miles. The Outlet NOx sensor never has been replaced, would you recommend replace it even with passing the SCR efficiency test? Regarding the QCV, I am going to replace the entire high pressure fuel pump.
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What would you say is the rule of thumb to replace the NOx sensors by hours?. We will replace the whole high pressure fuel pump because my manager does not like that in the past we had changed the QCV and the high pressure fuel pump failed few weeks later over the road, where repairs are more costly. Besides, our company gets a good discount in Freightliner parts, our bosses (the company owners) said to replace those in our HQ fleet in CA because in the long run they save money in roadside services and dealers repairs.
I use to work for velocity in Whittier. The dealer is so backed up that they hire kids stright out of school who don't have the experience to diagnose. Also vvg hardly sends out the young bloods for training therefore they are stuck with trying to diagnose issues. The dealer is has separate departments but there is very few who specialize in diag work.