I fanally got the code 171/174 issues resolved. Now a mire 20 miles after the emissions inspection the CHL comes back on. A serious "NOW WHAT" moment. I stopped by AZ and AA, neither knew what the code meant. A search here led me to find a unplugged hose on the DPFE. Very accurate. I crawled up on the engine and blew thru each hose and neither seemed obstructed. When I reconnected the hose the light did not go out.
How long will it take for the light to go out ? assumeing this was the only issue.

 

You may need to complete a few drive cycles without an issue being detected in order for the light to reset. Or you could pick up an inexpensive scan tool and reset the light yourself. If you have an Android smart phone you could use the Torque Lite (free) application and pick up a bluetooth OBD-II adapter for about $35.

-Rod

 

great, I'll keep an eye on it for the next few days. Now I just wonder why the dang thing popped off in the first place. Guess I'll put some tie wraps on the connections til I can get to the parts store for some proper hose.

 

Two possibilities, hose is dead and too loose (requires silicon hoses, 2 different sizes), or there is too much exhaust back pressure.... Philip

 

I did not realize they were 2 different sizes. Thanks for that. Can you tell me what sizes they are ?
I know I'm not going to like the answer, but what would cause "too much exhaust Back pressure" ?
The truck only has 85,XXX miles so I'm doubting the cat cons, altho they have been suggested before when I had the code 171/174 issues.

 

Just so you understand how the DPFE works, in the exhaust manifold there is a baffle plate, the nipples straddle the plate and the DPFE measures the differential between the pre and post nipple. when the pressure builds in the pre baffle nipple the DPFE signals the EGR to open.... The EGR must be closed at idle and low RPM, opening when the engine is at or about cruise. The induction of waste gasses acts to cool the valves and assists in the burning of raw fuel.

I suspect you may have slipped the hoses on the wrong nipples, however if you are to measure the back pressure pinch off the front hose and connect a low pressure gauge(0-15psi) to the other, @ 2000rpm you should have not much more than 3psi. Any higher reading, investigate collapsed or melted Cat. This measurement can also be taken at the upstream O2 bung.

Running a too rich exhaust mixture, oil contamination will exacerbate CAT con demise. I would suggest connecting a live data scanner and record the O2 readings pre/post CAT.....Philip

 

I can see this might take some time. I seldom have reason to get above 35 mph and usually drive 1-2 miles at a time.
Great info to have. I'm sure I might need it. That's about the way I figured the dpfe worked. Pretty sure the lines are not crossed. The front line goes to the front of sensor and the back in goes to the back (nearest firewall) of sensor.
I have been battleing (and finally won)a bank one and two lean issue for a couple years, so the cats may come into question after all.