Hard shifting, no speedo, abs light on and overdrive button flashing

[Toolman1991]

drove to my buddys, everything fine, left and truck ran up to about 3k, shifted finally very hard, my speedo aint working, abs lights on, and overdrive button is flashing, hooked code reader up, no codes, tried hooking to when truck was running, it killed it the first time, almost killed it the second and still no codes, talked to one guy, said the abs proprtional valve maybe the problem, any body got any ideas?? thanks

[madpogue]

VSS / circuitry, most likely. ABS valve wouldn't cause an inop speedometer.

Does the odometer still read the number, just unchanging? If so, prime suspect is the VSS or the wire to it. It's in the (rear) diff. It may also be the tone ring (the "reluctor") on the gear inside the diff.

If there's no number showing on the odometer, then it's the PSOM / speedo head, or power to it. There's a fuse to it, but you'd have to finger the owner's manual to look it up.

[anschutz1913]

I would say its the Speed Sensor. Try checking the wire for it. If its ok then replace the sensor.

Also when hooking up a code reader the key must be on with the engine off.

[madpogue]

What code reader are you using?

[Toolman1991]

had the switch on when trying to read the code, wouldnt the vss throw a loss of speed sensor code?, cant i ohm the sensor out to see if its bad,

[Toolman1991]

first used one from advance then a mac tool one

[anschutz1913]

Im not sure about it throwing a obd2 code. It will throw an ABS code though, which you said your ABS light is on.

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[madpogue]

Those scanners probably don't read our trucks (the Mac tools one MIGHT). You need an old Snap-On MT2500 with the right personality chips, an AF Scangauge, or AutoEnginuity software.

VSS, like the CPS, is unlikely to throw a code. Think about what it does. It just "blips" every time a tooth on the tone ring / reluctor passes it. Like the CPS, it doesn't have an "I'm working, but not sensing anything" state. So when it goes dead, it just doesn't "blip", and the PSOM and PCM just think the truck's not moving. (Likewise, with the CPS, the PCM just thinks the engine's not turning.) These kind of sensors are just a sort of switch that opens and closes X times per second, and the PCM counts up the times per second and translates it into a speed or RPM. Only a sensor that acts as a variable resistor, within a particular range, such as the ICP or EOT, can throw a code when it's out of range or wide open or shorted closed.

[anschutz1913]

Originally Posted by madpogue

Those scanners probably don't read our trucks (the Mac tools one MIGHT). You need an old Snap-On MT2500 with the right personality chips, an AF Scangauge, or AutoEnginuity software.

VSS, like the CPS, is unlikely to throw a code. Think about what it does. It just "blips" every time a tooth on the tone ring / reluctor passes it. Like the CPS, it doesn't have an "I'm working, but not sensing anything" state. So when it goes dead, it just doesn't "blip", and the PSOM and PCM just think the truck's not moving. (Likewise, with the CPS, the PCM just thinks the engine's not turning.) These kind of sensors are just a sort of switch that opens and closes X times per second, and the PCM counts up the times per second and translates it into a speed or RPM. Only a sensor that acts as a variable resistor, within a particular range, such as the ICP or EOT, can throw a code when it's out of range or wide open or shorted closed.

I beg to differ just slightly on the scanners.... i have one from advanced auto parts that works great. However i believe you are correct on the ABS come to think of it. I was going from experience from my sisters 98 f150 which does store ABS codes.


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[madpogue]

Your AAP scanner communicates with your OBS PSD? Have you actually pulled codes with it?