U029E- NOX Sensor "B"

[chessy56]

With ~84K on my 2 year old Silverado, I'm seeing yet another series of error conditions. The latest, being the U029E code which, per a web search, is a "Lost Communication With NOX Sensor B". The CE lamp also activates on the instr panel. Further, I am also getting intermittent displays of a DEF level failure that comes and goes (corresponding IP indicator sets & resets), which also displays 2 different messages related to "miles left, with the speed limited to 65 mph".

Via my Edge monitor, I see that my DEF tank pressure is at 0 psi until I drive a mile or two, after-which my tank pressure exceeds 70 psi. Clearing the error code immediately resets my CE indicator. Given that I've recently encountered intermittent P20EE codes (SCR NOx Catalyst Efficiency Below Threshold Bank 1), my hunch is that these faults are inter-related.

Could it be possible that the lack of (or low) pressure on the DEF tank is resulting in weak/NO fluid from the DEF tank, thus, impacting the catalyst efficiency? With "no communication" coming from NOX Sensor B, is this sensor clogging with soot (or, defective) and, would the lack of tank pressure also suggest a soot buildup at/near the DPF?

I'm beginning to have a strong dislike of all this emissions control bull S#!T. Per my OnStar reports, I have NO recalls for my VIN with the L5P Dmax. And I question if any repairs to this system would be covered under the remaining warranty on this vehicle.

Thoughts, anyone?
And Thanks again!

[chessy56]

update: Now getting a P041B code in addition to the U029E. DEF fault light comes and goes, but I can force it ON with "heavy acceleration" and after driving normally for a bit, the indicator resets. P041B appears to deal with EGR gas temperature.

Since this is part of the emissions system, my bet is that I'm on the hook for the repairs, given the 50K miles warranty limit. The dealership is hemming and hawing about whether it's covered- all depends on what the tech codes it out as (???) and if any given part(s) would be defective per GM!

[chessy56]

update: Repair tech @ dealership states it is the NOX sensor B that is faulting out. They have the sensor; however, the pigtail connector appears to be corroded (after only 2 years?). The GM p/n is 19355899. Their network shows ONE (1) connector available located in OH and that dealership states that it is required for a customer of theirs (and that they are getting repeated calls looking for one). No other sources found on the web show any available. GM Customer Care has opened a case and they "should be getting back to me in 2 business days".

So how did this pigtail connector deteriorate in only 2 years? Mounted too close to the exhaust system, unprotected from the heat generated during the Regen process? Within the next 80 miles, my speed will be limited to 65 mph and I've been told the part has no ETA from GM and that I need to keep my miles "local" until the part is installed. I head a $1000+ bill being tossed around.

I need to review my options for this exhaust system if I'm going to keep this pickup.

[DmaxMaverick]

Good to hear you have it nailed down to a probable suspect. I don't think I'd wait until GM gets their supply issues in order, though. You may be better off patching it together, such as using pins that fit, pot it with some silicone, and protect it with a fiberglass spark plug sleeve. If anything, it will allow you to confirm the problem, and minimize down time.

[chessy56]

exactly where is this sensor postioned? I looked for a breakdown on the sensors along the entire exhaust/emissions system, but I'm coming up with little more than generic diagrams. Would a subscription to AllDataDIY help with diagrams? I'm sure there'll be other (simpler) things that I might be able to do myself if I had service related documentation.

[DmaxMaverick]

I'm not sure where that sensor is. JK and others should, though. The NOx sensor should be about the last one in a line of the bunch. And yes, I believe an Alldata subscription would be helpful. Not only for location and description, but also the pinout of the connector, and perhaps an alternative for the connector that GM has but doesn't have. I don't have any L5P Alldata subscriptions (haven't had a need, yet), but that would be my first step if I had an issue such as yours.

[JohnC]

How bad is the connector? Maybe all you need, at least temporarily, is to clean up the connector.

[chessy56]

Not sure about the connector itself- I looked under the truck and found what I believe to be a pyrometer on the DPF (probably EGT sensor#4), a pressure outlet (which goes to a pressure switch, together with another- presumably pre-DPF) and another sensor that is only a 2 wire device. I thought the NOx sensor was a 4 wire device, so I'm not sure where it is. Between the #2 CAT and the SCR/DPF?

The shop is telling me the #2 NOx sensor is bad, so I'm sure it'll be replaced- but it hasn't been yet. We now wait on a lousy pigtail harness which is "on back order"! A bigger concern is being limited in speed (to 65) within the next 80 miles. Will I be further limited after that?

I've bitched to GM and they've opened a case on this- for whatever good it's going to do.

[chessy56]

So, it appears that the NOx sensor connector isn't the problem. It's a connector on the EGR valve from what I'm now being told- the shell/plated blades are described as "brittle" and the tech apparently felt that attempting to get this apart to clean up the contacts would result in the failure of the connector. GM states a new batch of connectors will be shipped to the distribution center by the end of the month- with a slow boat delivery to the dealerships afterwards. I'm estimating middle of May (2-3 weeks out) before my truck is repaired.

Meanwhile, I've been cautioned that I have ~80 miles left before being limited to 65 mph. After some additional miles, I'm limited to 35 mph and then 15 mph (all dependent on the soot level as the truck won't regen without the sensors intact). Emissions warranty expired at 50K miles, so I'm on the hook for rental car expenses. Looks like I'll be a home bound hermit for the next few weeks. The justification for parts deletes is becoming stronger, being that I've assumed the role of a Guinea Pig on a new engine platform....:mad: