Help with codes 63 and 31

Code related problems will get more attention in the 5.0 tech forum. This forum is for tweecer & similar tuner posts.

CODE: 31 (KOEO) - EVP circuit below minimum voltage. Vref (5 volt reference voltage supplied by the computer) missing or broken wire or bad connection in circuit. Use a DVM to check for 5 volts on the orange/white wire. If it is missing, look for +5 volts at the orange/white wire on the TPS or MAP sensor located on the firewall near the center of the car. Use the black/white wire for the ground for the DVM.
With the sensor removed from the EGR and still connected, press the plunger and watch the voltage change on the brown/lt green wire. Pull the passenger side kick panel and measure the voltage at the computer. You will need to remove the plastic cover over the wires and probe them from the backside. A safety pin may prove very useful for this task. Use pin 27, EVR input (brown/lt green wire) and pin 46, signal ground (black/white wire) to measure the voltage. The orange/white wire is Vref and should always be 5 volts -/+ .25 volt. Be sure to measure Vref at the EGR sensor to rule out any broken wires or bad connections.


Code 63 - Throttle Position Sensor (TPS) signal too low TPS. Vref missing (5 volt reference voltage supplied by the computer), bad connections or damaged wiring, TPS sensor failed, TPS sensor way out of adjustment. Use a DVM to check for 5 volts on the Orange wire. If it is missing, look for +5 volts at the Orange wire on the EGR or MAP sensor located on the firewall near the center of the car.
Try this... Currently there is some dispute about setting it at .99 volts but anything less is probably OK. All you need is less than 1.0 volt at idle and more than 4.25 at Wide Open Throttle (WOT). You'll need a Digital Voltmeter (DVM) to do the job.

Here’s a TPS tip I got from NoGo50…

When you installed the sensor make sure you place it on the peg right and then tighten it down properly. Loosen the back screw a tiny bit so the sensor can pivot and loosen the front screw enough so you can move it just a little in very small increments. I wouldn’t try to adjust it using marks. Set it at .97v-.99v, the closer to .99v the better. Just don’t go over .99, or you upset the fuel calibration and idle quality will suffer.

(copied from MustangMax, Glendale AZ)

1. Always adjust the TPS and Idle with the engine at operating temp. Dive it around for a bit if you can and get it nice and warm.

2. When you probe the leads of the TPS, do not use an engine ground, put the ground probe into the lead of the TPS. You should be connecting both meter probes to the TPS and not one to the TPS and the other to ground.

3. Always reset the computer whenever you adjust the TPS or clean/change any sensors. I just pull the battery lead for 10 minutes.

4. Check the procedure for your year, on my 90 I have to turn the idle screw until it just touches the tab, then insert a .010 feeler gauge and give it about one more turn. Then you adjust the TPS voltage to .98v, reset the computer. Start it up, if the idle is to low then turn the screw in until it is just right, then readjust the TPS voltage to .98v and reset the computer and start it up. The key is to adjust the TPS voltage and reset the computer whenever the idle screw is changed.

Clean and check thre 10 pin salt & pepper shaker connectors up near the EGR valve.

hey guys, i have codes!!! i think that i bought a headache that i thought was a good deal. im new to this site and still learning how to navigate. i have an 89 gt that has a factory rebuild with a 303 cam, full exhaust, hi flow water pump, 160 tt, oil pump, cai, clutch, 410s, 70mm tb, msd. i have an intake pop and 5 codes... 63 85 29 33 64. i know the mechanics, but the computer codes are betond me.there is no egr. no a/c, where do i start????

reciprocation23 said:

hey guys, i have codes!!! i think that i bought a headache that i thought was a good deal. im new to this site and still learning how to navigate. i have an 89 gt that has a factory rebuild with a 303 cam, full exhaust, hi flow water pump, 160 tt, oil pump, cai, clutch, 410s, 70mm tb, msd. i have an intake pop and 5 codes... 63 85 29 33 64. i know the mechanics, but the computer codes are betond me.there is no egr. no a/c, where do i start????

Click to expand...

Is your mustang running? I would double check the engine timing and firing order to be safe also do you know if the guy changed the springs on the heads? if not an e303 cam is to much for stock springs
code 63 -you need to set the tps sensor to .999
code 85 -cannister purge, is yours connected?
code 64-air charge Tempreature,is your sensor in the lower intake connected

Sounds like the TPS and ACT are not even there, or not pluged up. 29 is a VSS code, make sure thats pluged in on the side of the trans where the speedo cable is.