[coloradohoosier]

Thanks for the help so far, but I was asking too many things at once. My 93 E250, OBD I, 5.8 gave me a 123 code, TPS exceeds max voltage. I've just been trying to test it with my multimeter using the Hayne's book I have, and I'm a little confused about the instructions the book gives. Under TPS Check, it says to use the voltmeter to test on the 'backside' ---- the illustration looks like that means the harness side, but it isn't completely clear ---- backprobing the SIG and SIG RTN, looking for 0.5 to 1.0 volts. If 'backside' means harness side, I'm quite confused how this would test the TPS --- it seems like it would be testing whatever sends power to the TPS. Adding to the confusion, is that after that check and a check of reference voltage, it says to check resistance of the potentiometer, which specifically says to use the ohmmeter on the sensor side, which seems to confirm that 'backside' means harness side.

(GRRRRR)

I tested the harness side, and my reference voltage was 4.96. I got eratic voltage between SIG and ground, but not within specs (0.5 - 1.0 at idle). Checking resistance on the sensor side, I got no ohms. I concluded I must need a new TPS, and opted for a junkyard $8 one instead of a new $33 - $44 one. I also picked up a throttle body gasket, because the TPS is on the bottom of the throttle body. Did the swap, but nothing changed. CEL is still on, idle still won't drop once she's warm.

[Skyhawk]

Back-probe; I use a straight pin and incert it so that it touches the pins in the connector rather than puncture the wires and open the wire to corrosion. So, the TPS has two tests as follows:
VREF (voltage reference) Key off and wait 10 seconds. Disconnect the TPS connector Probe the VREF ( (brown/white wire) and the SIG RET wire (gray/red wire) at the TPS connector. Put the key on engine off (position) and look for 4 to 6 volts. If not look for VREF circuitry and wiring problems.

Test 2: KOEO back probe TPS (gray/ white) and SIG RET (gray red)and move TPS from closed throttle to full open throttle and look for 0 to 5 volts . If not, faulty TPS. Note: any break in voltge as the Throttle is moved indicates a "flat spot " in the TPS and the TPS should be replaced. This commonly causes "stumbling" as the throttle is advanced.
Use a digital multimeter and an LED test probe on these electronic systems rather than an analog meter of an incandescent probe.

[Guest]

How do you know that the used part isn't bad? Keep in mind that just because a code is thrown doesn't necessarily mean that the part is bad, it just means the PCM is not receiving the correct feedback from the part. The wiring can have a problem, etc. I had a DPFE code the other day that ended up being a break in the wire right at the terminal connection for the DPFE. Since the DPFE has a high failure rate, I automatically assumed the DPFE had failed. Much to my dismay, it was not bad at all. So I now have a dull DPFE, and a shinny new one.

Good luck.

[MichaelJennnings]

Originally Posted by coloradohoosier

Thanks for the help so far, but I was asking too many things at once. My 93 E250, OBD I, 5.8 gave me a 123 code, TPS exceeds max voltage. I've just been trying to test it with my multimeter using the Hayne's book I have, and I'm a little confused about the instructions the book gives. Under TPS Check, it says to use the voltmeter to test on the 'backside' ---- the illustration looks like that means the harness side, but it isn't completely clear ---- backprobing the SIG and SIG RTN, looking for 0.5 to 1.0 volts. If 'backside' means harness side, I'm quite confused how this would test the TPS --- it seems like it would be testing whatever sends power to the TPS. Adding to the confusion, is that after that check and a check of reference voltage, it says to check resistance of the potentiometer, which specifically says to use the ohmmeter on the sensor side, which seems to confirm that 'backside' means harness side. (GRRRRR) I tested the harness side, and my reference voltage was 4.96. I got eratic voltage between SIG and ground, but not within specs (0.5 - 1.0 at idle). Checking resistance on the sensor side, I got no ohms. I concluded I must need a new TPS, and opted for a junkyard $8 one instead of a new $33 - $44 one. I also picked up a throttle body gasket, because the TPS is on the bottom of the throttle body. Did the swap, but nothing changed. CEL is still on, idle still won't drop once she's warm.

Junk yards are good for hard parts, like bumpers, body panels etc, not for electronics. These parts are usually damaged from weather, people hitting them, prying on them. You get the picture. When you check signal return to ground is where you will get the .5=1.0 volts @ closed throttle with the key on engine off. Actuating the throttle to WOT should increase the voltage to near VREF. If when you check these it jumps, or doesn't increase at all or is out of range at the start, replace the TPS with a NEW one. Should the TPS you used be defective in any way, it can cause SEVERE engine drivability issues. It can actually cause the IAB to allow too much air through causing the vehicle to accelerate uncontrollably.
On electronics, please spend the extra monies and go with new parts not junk yard parts. It just isn't worth the risk. Plus, these parts are all coded by the calibration code of the vehicle. Just because they say it is from a 2004 Taurus, you don't know if it is the same calibration as yours. There are many different codes for every model and year vehicle.

As for back probing, there are a number of manufacturers out there that make breakout harnesses to do this with. They usually aren't that expensive and if you want to do this yourself, it would be a good investment since you already have a DVOM and the OBD Tester. Most of these harnesses are single wires that plug in between the harness and sensor that have a hole in them to probe with the DVOM leads. Makes it very simple and easy plus you don't risk damaging the harness at all. A set that has 4 wires in it should be all you need to complete your test set.

[Canuck623]

Did you disconnect the battery after you replaced the TPS? If no then do it. The older OBD 1 cars and trucks had this weird thing about not knowing they were fixed after a part replacement. Reset the fuel settings by disconnecting the battery and let us know.