Ambient air and DEF problems and solution

[trdodd07]

I've been having ambient air temp sensor issues as of late, and along with it, DEF codes as well. When checking in Insite, it would read up in the 160* range and would work up to 200*.

2398: Ambient Air Temperature - Data erratic, intermittent or incorrect
1679: Aftertreatment 1 Diesel Exhaust Fluid Tank Temperature - Data erratic, intermittent or incorrect
1681: Aftertreatment 1 Diesel Exhaust Fluid Dosing Unit - Bad intelligent device or component

1) When looking at the descriptions of the codes in QuickServe, for the DEF faults, it mentions that a faulty ambient air temp sensor is a possible reason those codes would become active, and with that, would disable the DEF system. So, if you see these DEF faults, you may want to try a new ambient air temp sensor first before digging into replacing DEF components.

2) My Cascadia has 2 ambient air temp sensors, one on the left and one on the right. Both are located behind the bumper, however, they may vary from truck to truck. Mine is a 2012, so I'm not sure if that is where they placed them for that production year or what. With that being said, one sensor communicates with the truck information center on the dash, and the other communicates to the ECM. When I initially looked to replace it, I looked in quickserve. Well, it mentions an Ambient air PRESSURE sensor (Barometric air pressure) which is located near the IMAP sensor on the engine harness, on this 2250 anyway, but does not measure temperature. 2nd try was at a Freightliner in Texas which could only find one sensor out front behind the bumper. So, I gave it a try but did not fix the issue. Temp would still read up in the 160* range and would work its way up to 200*, which would then set a fault in the ECM. Checked again with a different Freightliner in Grand Junction, CO, and they had to do a little bit of some digging to find the correct one. It was named Air temperature sensor, instead of ambient air temperature, lol... Plugged it in and checked it on Insite and all seems to be well, and reading the correct temp.

This is the AIR TEMPERATURE sensor located on the drivers side behind the bumper (pretty close to being right in the middle actually)



This is the AMBIENT AIR TEMPERATURE sensor, located on the passenger side behind the bumper



Air Temperature Sensor part #: 06-74220-000
Ambient Air Temperature Sensor part #: 22-72747-000


Moral of the story... When facing DEF faults regarding the ones mentioned above, check your air temperature sensor first before replacing Doser units and tank temp sensors. And, when/if you do replace that sensor.. make sure you're getting the correct one because they are not swappable.

[Rawze]

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Wow! -- That is a nice article and you have pictures and part numbers too. Thank you for taking the time to do this for everyone here on the forum. I am sure it will help others.

[trdodd07]

(08-21-2016 )Rawze Wrote:  .
Wow! -- That is a nice article and you have pictures and part numbers too. Thank you for taking the time to do this for everyone here on the forum. I am sure it will help others.

Just doing what I can to hopefully make it easier for the next person with similar problems.

I did forget to mention, in Insite on the Features and Parameters list, OEM ambient air temperature sensor can be enabled/disabled. So, there is a possibility that some trucks may not have that sensor, or, you may try to disable it, though I think the DEF system relies on it's reading to operate.

I think the DEF system cross checks the tank temp with the ambient air temp, and if there is a large difference (54*F according to quickserve), then it will set the 1679 fault. With that, it thinks that there is an internal error with the DEF controller or dosing unit, and then disables the system.