I have had this problems and was able to fix them so for future guide I decided to write in "English", what you are facing and solutions. Spn 4334 7 is basically telling you that no or little def is reaching the meter unit and is not spraying enough of it to the aftermath treatment. There's many possibilities, but you should check in a priority order. A Do you have spn 4335 1 also present? If answer is yes, you most likely got a bad air pressure limiting unit. The unit is connected directly to your secondary air tank, any leak of oil or moisture will deteriorate the unit it just won't do its job no more. Best way to check this is dismaying the air hose from the meter unit and start the truck. Leave it running for a few minutes and then stop it. Check the hose for any oil/moisture if there's any, your pressure limiting unit is not working properly or at all. Replace all hoses and the unit itself. Install a air compressor filter so to protect the unit in the future. Don't go crazy by a bit of oil and replace the compressor etc., a small leak is normal on every truck is just that this unit is too sensitive and the manufacturer did not put a filter to protect it. Check it on pic 1. B spn 4335 1 only, which is unlikely but possible, the meter unit is not getting air, so there's basically 3 possibilities, 1 meter unit is clogged with crystalized def, 2 a hose broke and leaks air or 3 the pressure limiting unit got the same problem as above. Unasemble the passenger side skirt, take the iron box protecting the meter unit is on your left, visually check for crystalized def, take the hose out and unassemble the valve check for any contamination and or crystalized def. same for the line going down to the sprayer check for the same staff. If you see any flush the meter unit as directed by freightliner, you'll need to remove the meter unit which is a pain in the rear so if you're not a wrench guy take it to a dealer. 2 air leak. If any of the hoses has a severe leak you should have noted that on your dashboard already, if that and the code are present simple math are correct, a hose is bad. You are lucky I replaced all the 3 hoses for $6 bucks! That will do with spn 4335 1 4334 7 is similar but instead of air is def. since def is stored on a tank is goes through a bit more complex sistem to get it where it needs to go. There are several hose lines that keeps your def flowing they are the blue hoses you see on top of your def tank. You got a pump, a filter and also is air. If only spn 4334 7 is present the most likely problem is crystalized def in your air valve. Go under the truck get the metal protector out and visually see if there any crystalized def behind your def tank, if so unassemble all hoses and clean them with hot water that will do. Let them dry ... Def filter is full replace it. There's no real way to tell if it's the filter or crystalized def before hand. If you got this problem go ahead and replace the filter as first thing unless you know it got less than 100.000 miles. Then go for crystalized def and last for the air pressure limiting unit. It could also be a bad pump, since it might be ok for voltage etc. But is not doing its job 100%. This I don't have a way to check it since you'll need an expensive computer and I don't own one. Basically what the codes are telling you is that the def lines/air lines need service, and to fix it you'll need to go to the root of the problem. In my case I unassemble all hoses and didn't find any cristalized def as suggested, but rather a full def filter and then a bad pressure limiting unit, it got lightly contaminated and needed replacement. You should install a filter also to protect your aftermath treatment and the week air unit. Hope it helps. I might left something behind, I'm on a cell phone and typing is kind of bad. http://www.ddcsn.com/cps/rde/xbcr/ddcsn/301-12.pdf https://ddcsn-ddc.freightliner.com/cps/rde/xbcr/ddcsn/622-12.pdf This two documents will guide you. Add the filter and pump to the equation.
It depends on the truck you got mine are: A0001420289 original Baldwin PE5272 You can call a dealer with your vin number and ask them the part number.
Is there supposed to be air to the metering unit at all times? I’m not getting air past the air pressure limiting valve. Just put a new one on there
