machine23

my cel has been on for almost a year now, with the same 71 code which would be the egr malfunction code. in the past year i have changed out all egr components including the thermal vacuum switch on the back of the intake manifold. So my registration expired back in august, and i had to smog it to bring my reg back to current. after every changed egr component i reset my ecu and waited to see if the light came back. and every time it did. so i finally took it to smog yesterday, and just reset my ecu in the parking lot. it passed. weird thing is on my way home the light came back. for the same code. but on the paperwork for smog, everything smog related on the engine works, including egr stuff, and it passed beautifully, emission numbers are low. i dont get it. and it seems like my mileage is not as good as it was a year ago before the light came on.

i can reset my ecu and my light will come back after 10 minutes of freeway driving. but it will stay off if i am only going 30 or so through town

any ideas? why would it continue to show me the cel for 71 if every thing is working properly

scope103

Because everything is NOT working properly. The smog testing system relies on your ECM to point our malfunctions that they don't manually check for. That's why you flunk smog if your CEL is on, no matter what the tailpipe gases say.

And you're lucky you passed.

DO take a look at the actual text for code 71 http://www.ncttora.com/fsm/1990-1995...e/diagnosi.pdf (page EG2-176) Most of the indicated repairs have nothing to do with replacing parts. And the diagnosis path is not too difficult. http://www.ncttora.com/fsm/1990-1995...n/exhaustg.pdf

One common issue with our older trucks is "gunk" in the plenum (upper intake manifold) blocking the EGR tube. But since you passed on the tailpipe gases, you may have a partially working system.

Good luck!

smogman

either your egr has no vacuum or the egr passages are blocked/restricted or the EGR temp sensor is bad. You have to diagnos it.

Sensei

You got lucky, either your smog tech is an asshat or you got a nice connection. Your good for two years so why worry.