How to Drain Poor Quality DEF Fluid???

[sierra2500HD]

So... not quite 3 weeks after the last visit to the local GM service center I once again get the "Poor quality DEF fluid" warning in the DIC. Now I know it's not the DEF because they drained it and replaced it (and charged me almost $200). I mentioned they might want to check the NOx sensors but that suggestion was shrugged off as irrelevant.
The shop kept the truck overnight and ran a 2 hour high idle test (almost ran it out of fuel too) and told me that the catalytic converter was bad and needed to be replaced. A new one was ordered and installed the next day.
No charge this time, and I'm hoping it's fixed but we'll see.

[WildChevys]

subd

[GMCustomerService]

I'm so sorry to read about what's going on with the truck, sierra2500HD! Please, let me know how things go this time around.

Michelle, GM Customer Service

[sierra2500HD]

Got the truck back on Friday afternoon (11/2). The catalytic converter and an exhaust temp sensor were replaced. They didn't do anything with the NOx sensors. Obviously they also reset everything. We'll see how long it runs before throwing the "Poor quality exhaust fluid" message again.
BTW, this problem also shows up in a lot of threads on the dieselplace.com forums. For example see LML: #PIP5007: Exhaust Fluid Quality Poor Message Difficult To Clear - Diesel Place : Chevrolet and GMC Diesel Truck Forums

[DLB]

Just got back from dropping my truck off for the second time after getting the "DEF poor quality" on the DIC and CEL. The first time they just cleared the DTC and reset it. Ran for maybe 40 miles and it came back on. I mentioned it may be a sensor.

[DLB]

Just got a call from the service dept. They asked where I buy my fuel, but didn't elaborate on why that may be important. I told them Kroger and BP mainly. Said ok and they'd call me back.

Anyone want to speculate on why that would be important concerning the DEF?

[redwngr]

DEF poor quality is determined by the NOx sensers not seeing the expected change in NOx level for the amount of def being injected. The system assumes that if it is not getting the expected response that it must be because of a def problem.

Many have reported def quality warning be correction by NOx sensor replacement. (and almost never by draining and replacing the fluid.)

Speculation: This is assuming that the replaced parts you referred to includes previous replacement of NOx sensors. The dealer may be wondering poor quality fuel, or poor fuel additives, may be coating the NOX sensors and causing incorrect readings.

Are you running any fuel additives?

[DLB]

Thanks redwngr. They haven't actually replaced any parts yet. The first time I took it in they checked the DEF quality and cleared the code. Drove less than 150 miles, and the DEF light and DIC lit up with the poor quality message. That makes sense what you're saying about the NOX sensors being coated. They have had my truck for 3 days now, so hopefully they are troubleshooting. They called me about an hour ago and said they'd need it for at least another day.

As for fuel additives. The first time I got the DEF poor quality light, I wasn't running anything. Straight diesel. Since then, I added 10 oz of Stanadyne when I filled up at BP. I should know more tomorrow.

[GMCustomerService]

Keep us posted as well DLB. Feel free to contact us directly if you find that you need additional assistance. Thank you.

Tricia, GM Customer Service (Assisting Michelle).

[sierra2500HD]

This is getting ridiculous - the "Poor Quality DEF Fluid" warning just came on again this weekend. I'm really getting sick of this nonsense and not looking forward to taking it back to the dealer for the 3rd time.
AAARRRRGGGHHHH!