So I was poking around under the dash and found a connector unplugged, when I plugged it in the emissions light came on. The connector (3 wires?) plugs into something that looks like a relay. Now I know why it was unplugged!

What is this light telling me? The shop manual is real vague on this one.

Is this a timed service interval type of light (resetable?) or is it indicating a problem?

The truck failed the emissions test, so I checked the computer's codes and discovered that the O2 sensor had failed. I also replaced the EGR valve since it was blown. My emissions troubles are now over the truck passed with a "fast pass" so I guess my next move will be to reconnect the light harness. Just looking for some background info.

Thanks!

 

Whoever replaced the O2 sensor should have cleared the codes or disconnected the battery for 1/2 hr to clear the codes.

The problem triggers the service light and stays on until the problem is fixed.
Apparently the P/O decided he would rather disconnect the light

 

Years ago when my 86 hit 60K miles and the check engine light came on, I was told by a service manager that Ford programmed the 60K benchmark into the computer so that the entire emissions system could be checked and several parts replaced as necessary. Tech's were required by law to perform all tests before the computer could be cleared. General cost for this service back then was around $700.

I took the dash apart and removed the lightbulb. That was 250K miles ago.

 

There's a small module called the "Extended Useful Life/Inferred Mileage Sensor" in the dash, and that's probably what you found. It's "inferred" because before '87, there was nothing on the truck that electronically measured actual mileage, so I suspect it detects runtime. It might kick in at 10,000 mi on a vehicle that spent a lot of time at idle or in low range, or at 100,000 on one that was used for long highway trips.

 

The emissions light is totally independent of the computer also. Scroll to the bottom here for the reset procedure.

 

Thanks Brown, Excellent information. I knew sombody had came across this issue b4 me. I will try it today at lunch.

-B