DEF Shelf Life!

jjr1314 wrote:
Oh and P.S. I never intended this thread to be a Ford vs GM vs Dodge battle. Just wanted to pass on my recent experience with DEF and what I learned from 2 different dealerships about GM's warranty as it pertains to Duramax emissions control system so others on here would have some info.

You keep talking about problems with DEF, but the issue wasn't DEF. It was a NOX sensor that went bad. The DEF had nothing to do with it.

They system injects DEF into the hot exhaust. The urea in the DEF becomes ammonia in the hot exhaust gas. The ammonia reacts with NOX in the DOC to make nitrogen and water vapor.

The NOX sensor downstream of the DOC monitors NOX and adjusts the DEF flow to control emissions. If it's commanding DEF flow and doesn't see a NOX reduction the computer knows something is wrong and defaults to the "Bad DEF" display. the only way they'd be able to monitor the sensor is by putting more of them in and comparing readings. That's what you do for large stationary engines, boilers, furnaces, etc. It's not a practical or economically reasonable solution for mass produced automotive applications.

I think the engineers did a pretty good job with what they had. It wasn't their idea to force the limp mode. The EPA mandated that. They (the EPA) probably figured it was the only way to ensure compliance with the new emissions regulations. Their goal, after all, is to help keep the air clean. We've gone through this with gas engines and now we're going through it with diesels. Face it, without the limp mode hardly any of the DEF/DOC systems would be fixed after the first issue. Many would not even have the DEF refilled after it first emptied.