Trouble Code P040B - Ex. Gas Temp Implausible signal
 

2014 3.0 TDI: Well after replacing the gaskets and seals for the Oil Cooler, EGR Cooler, and the Coolant Diverter Valve, and related items...all seemed well. An initial test drive of only about 5 miles and no issues. The next day I make my 40 mile drive to work and back with no issues. But the following day, just as the motor was getting up to operating temps, the CEL popped on. I had my laptop and VAG cable with me so I checked and got Code P040B...exhaust temp sensor bank 1 implausible signal. I was hoping it was related to all the work I just did, so I cleared the code and and continued driving - it did not return. Then at lunch time I was going out for a bite and within a mile the CEL popped on again, same issue. Now I'm a little worried. I checked the electrical connector it looked fine, unplugged - replugged, cleared the code and it did not come on again during the drive. Then on the way home it popped on again. I hooked up Vag-Com and logged some data for the exhaust temps of bank 1 and 2. Bank 1 hovered around 190C while bank 2 hovered around 245C. I don't know what the operating parameter are supposed to be, but based on the difference between banks 1 and 2....I assume the sensor may be bad. I will do some more testing tomorrow on this.

Any feedback on this is welcome....thanks gang!

Just a follow up on this. Code P040B would pop up sometime just before the motor reached operating temps. I would clear it, and it would not pop up again during the drive, even with multiple stops and starts. But sometime the next day it would come on again. Internet searches suggest the EGR Cooler is bad, but I doubt that as this whole mess started only after I did the work. The temp sensor (thermocouple) could be bad, it's located behind the oil filter housing...not too expensive if I need to replace it.

Another code recently popped up...P245B Exhaust Gas Recirculation Cooler Bypass Control Circuit - Implausible Signal. Now I'm thinking I may have screwed things up when I did all the oil cooler and egr gaskets & seals. So if things continue I will be pulling the intake manifold back off for a closer look. The packaging on these TDI's is so tight you can't see anything. I'd like to have a heated discussion with engineers who designed all of this crap!

One thing I noticed was that these codes have an "Unlearning Counter = 40". Not sure what this means, perhaps it means that the code will be present until there are 40 start cycles without issue? Well....after continued drives the CEL turned off and hasn't popped back on. I'm suspicious...and hesitant to believe it healed itself. Time will tell.

Well....the codes popped on again this morning, about 45 seconds after start-up. So...I will pull off the intake manifold this coming weekend and see it there is anything visually wrong - such as maybe a loose vacuum hose, etc. Crap.....

Just for fun, I disconnected the EGR Temp Sensor to see what the results would be - Code P040 signal too high. So it's looking like the sensor may indeed be bad. I cleared the codes from this morning and let the motor run for a bit - no issues, nothing in the "pending codes" either. NOTE - One thing about the P040 Code is that a record of this code kept as a "permanent code" - and cannot be erased.

Sorry; I haven't intentionally been ignoring this forum.....

Considering the possibility of a circulation issue, did you release the air from the small bleeder screw on the top left side of the EGR cooler? If not, it's possible that you aren't getting proper circulation through the cooler.

HI Wes....no I didn't check for air in the cooler - but will do so tonight. Thank You for pointing this out.....I do appreciate it. Due to a death in the family, I will soon be making a 900 mile drive up to Michigan, and I haven't had time to dig into whatever issues may be happening. As for as the temp gauge on the dash, everything is right where it should be, and the motor has been running perfectly. But I do worry that if I let things continue....something bad will happen. I would hope that when the engineers designed this "Rube Goldberg" EGR system that they took into account certain failure modes such as the diverter valve, or a vacuum valve...and that there was some redundancy to prevent a catastrophe.

Condolences to your family; I hope the memorial services provide comfort and closure.

Thank You -Wes- ....I am driving up to Michigan on Sunday morning. I have not had time to dig into things regarding this "EGR Temp Implausible Signal" issue yet. I will try and bleed the coolant at the top of the EGR Cooler first. Then I will likely pull the intake manifold back off and see if I need to clean the probe end of the temp sensor. While the intake is off, I will try and see if there is an issue with vacuum hose connected to the Coolant Bypass Valve. There is one other thing that concerns me. When I was in putting everything back together a week ago, I was sort of laying on top of the motor at one point, and broke the vacuum hose off of the valve on top of the EGR Cooler. There is a sort of a protective shroud around this vaccum connection, I inserted the vacuum hose in there, and used sealant to seal up the hose to the shroud - hope this makes sense. Not sure if this is also a problem. Unfortunately this vacuum valve is not an item that can be replaced - you have to buy a whole new EGR Cooler.

:eek: Well, hopefully that "shop fix" is not the issue.

On the bleeder screw, you can just remove it while the car is off, and it should either dribble a little coolant or seem to do nothing. If it does the latter, tighten it up again, drive the vehicle to full operating temperature, then loosen up the screw again while it is running. Don't remove it completely, as fluid could come out with gusto, but just loosening it well should allow for the air to escape and a tiny bit of fluid to sputter/spit then dribble. At that point, it should be good to go.

Thanks Wes....I did remove the intake tube and EGR pipe and cleaned the temp sensor - it was pretty dirty. I also discovered a very slight leak where the EGR pipe joins up to the intake tube, so I fixed that as well. My fingers are crossed that all is good. I did start her up and watched some live data and the sensor was reading temps. Also checked the coolant level - exactly where it should be, so at least all of those gaskets and seals I replaced are holding. I really do love this vehicle, and treat it with kid gloves, no hard acceleration, easy driving during warm up, nice long cruises...it's such a nice ride. I hope it understands my well-wishes and good intentions....and reciprocates :-)