I just bought the truck with 160300 miles on her. I found that when I went for the test drive, the CEL stayed on the whole time and was on at start-up. The PO seemed surprised when I mentioned that I will have a time getting it to pass smog, and he asked why. I mentioned the light, and he said he would have it fixed, but in actuality, I used that as bargaining material on the price. ( shame on me ) The truck ran smoothly and flawlessly on the way back home.

Before getting it home, I stopped at the local Auto Zone to have the codes read.
KOEO showed a 31 (EVP signal was/is low/ or out of range). The Zone guy mentioned I needed the EVP sensor.
The KOER showed the same 31, and also 67. Little did I or the Zone guy know at the time that it meant..."Depress the clutch during the test you big dummy". Anyways.... I didn't buy anything, and drove it home. I searched google for the codes and found this forum.

I searched a bit and found some tests and things to look for. I ohm'd out the EVP sensor, and found it within limits. I checked to be sure the EGR was closed during idle, and would open when vacuum was applied. ( Bypass tube was cool and idle was smooth when closed, and the tube warmed quickly, and idle was rough when it opened) I pulled the EGR and found it relatively clean, but cleaned it while I had it out, and proved it was sealing while closed. I re-installed the EGR, and tried to reset the ECM by pulling the battery cable for 30 minutes.

I restarted the engine and the CEL came on instantly,and remained on. I took her for a test drive, and all seemed just as smooth as it was before. I ran the code scan again and received the 31 during KOEO, and 31,13 (Idle spd control motor or air bypass not controlling idle properly),and 25 (knock sensor not tested - ignore if not pinging) during KOER.
I checked all the connectors I could see in the harnesses, and checked for vacuum leaks with brake cleaner while running. Didn't find any problems, then ran the code test again. I intermittently find different codes popping up during the KOER tests with 31 being a constant during KOEO and KOER, and decided to tackle that problem 1st. I bought a new EVP sensor, and found the same 31 when tested with it installed. (mind you, I'm trying to clear codes by pulling the test jumper in the middle of the test, and pulling the battery cable for 30 minutes. I still get the 31 during KOEO and KOER. I research a bit more and have found that sometimes it's necessary to file the end of the push rod on the sensor, because apparently the EGR diaphragm can become warped and position the push rod in a position that the ECM reads as a problem with the voltage being higher than it should be when the valve is to be closed at idle.(less resistance allowing for more feedback voltage when valve is closed)

I didn't find anything on the warppage being in the opposite direction to cause a low voltage reading, so I experiment and add a rubber bumper on the end of the push rod to see if the code would change to 34 ( EVP sensor is/was high). I try and reset the ECM again, and before starting the engine, I get code 31. I then run the KOER test and find 34, as well as other codes (including a lean code). I leave the garage with the CEL still on and go to the Zone to get the Haynes manual, and before I get there, I notice the CEL had gone out. I come back home, and still find the 34 in both modes of code reading all by itself ( no other codes).
So with all that said, do I have to replace the EGR because of the problem I still have (31,34), and what's up with the other intermittent codes being found during the ER scans? If I get 31 taken care of, will the intermittent others keep me from passing Smog?

Sorry for the long winded post,but I'm just wanting to be clear on what I've done and have experienced. Thanks for any help anyone may be able to provide.

Edit: Why wouldn't code 31 be erased when I tried resetting the ECM after the rubber bumper was added to the EVP sensor, moving the position of the pushrod to get code 34?

 

Well, A for effort! But try to break up your paragraphs next time on a long post. It starts turning into a big blur 1/2 way through & hard to pick out key points.

Are you sure it's the "CEL" & not the "Engine" light?
My Vote is the EVP sensor's pooched, & while the idea about modding the shaft is thinkin outta the box,.......not the right box, this time. Most of your odd ball codes were probably because the scan was done w/ engine not at norm. op. temp. or operator error. Anyway, welcome to the Forum, your catchin on quick!

 

Paragraphs have been created .

It's the amber light marked with an arrow in the picture .



The EVP sensor has been changed with the same result.

 

The KAM will clear after only 5 minutes of the battery disconnected. Yep, that's a lit CEL. Saw another pic just like it in National Geograph,.........wait, that's not where I saw it!

 

Hello again... CEL (codes 31 and 34) problem is a thing of the past. A new EGR valve with a new EVP sensor solved the problem. She passed smog with no problems.

Now on to a new issue in a new tread coming soon.....