31 code
Thread Starter
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Tuned
Joined: Jun 2006
Posts: 420
Likes: 3
31 code
hey guys, i've been trying to track down this 31 code for quite some time now on my 1990 5L. so far i've replaced the egr (due to a 33 code), the egr sensor, checked to make sure the egr tube wasn't blocked or plugged with carbon, the solinoid that controls the vacume line is getting 12 volts with the ignition on, and the oms are within specs. the egr sensor is getting the required 5 volts from the harness, and i've even gone as far as to stuff rags in the exhaust to create backpressure. each time i do something i unhook the battery to reset the codes. the only thing done to my truck is a true dual exhaust with full length headers. any help would be great.
New User
Joined: Feb 2007
Posts: 24
Likes: 0
From: Arlington TX
31= EVP voltage too low. Check the voltage at the EVP sensor (should be just under a volt, IIRC with the valve closed), and at the PCM (pin 27). There may be an open in the wire going from the EVP to the PCM, or a defective EVP or PCM. This system is not sensitive to changes in exhaust backpressure like the newer ones using DPFE sensors; the EVP merely measures how far the EGR valve diaphragm has moved.
Thread Starter
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Tuned
Joined: Jun 2006
Posts: 420
Likes: 3
great thanks for the replys guys. so loepke, you mean with the harness plugged onto the egr sensor the sig wire should be sending back just under a volt closed? lv2race i unplugged the neg terminal after i changed the sensor, i didn't think i would need to unplug before.
New User
Joined: Feb 2007
Posts: 24
Likes: 0
From: Arlington TX
Yes, the signal wire should have just under a volt on it with the valve closed. If you find that it does, then check pin 27 at the PCM for the same reading. If you have correct voltage at the PCM, you probably have a bad PCM, but it's more likely that the EVP sensor or the wiring is the problem (but you wouldn't have the correct voltages if that were the case). Just take the voltage readings and see what you get.
