4l80e no speedo

[Phew]

Ok, yes I've searched and searched and tried multiple different solutions to try and fix my issue. All speed sensors where changed one in the t case and trans, wire traced but I still have no speed reading at the ob2 port. My scanner driving down the road shows 0 mph. Any body got any other ideas what or where the problem could be ?

Also on a side not my tach is always off according to my scanner as well, at idle the dash will show 1100 rpm and the scanner will read 650-700. There is also an abs light on but I'm guessing that is due to the computer not seeing any vehicle speed

Any help would be greatly appreciated right now, I'm starting to get really frustrated with this thing

Truck is a 97 k3500 with a 454.

 

[Carlaisle]

Have you checked to be sure voltage is getting to the sensors? They can't send any data to the computer if they don't have power...

The stepper motor that controls the tach could be bad, although I've never heard of one failing like you describe. Seems more likely someone pulled the needle at some point and did not get it reinstalled correctly.

 

[Phew]

Have you checked to be sure voltage is getting to the sensors? They can't send any data to the computer if they don't have power...

The stepper motor that controls the tach could be bad, although I've never heard of one failing like you describe. Seems more likely someone pulled the needle at some point and did not get it reinstalled correctly.

Yes, checked for voltage from speed sensor and it goes up and down with throttle. Had it up on Jack stands and tested it on ac volts.

I'm at a loss with this truck, it's now decided to start bucking and stalling at about 2k-3500. Runs like a ***** ape wide open but it's a nightmare to get it around on the street. I'm at my wits end with this thing, getting tired of trying to fix it. The only code that shows up is the vss code.

 

[Carlaisle]

You should be testing the sensor with DC volts. Not much AC power in the vehicle's circuits. Where did you plug in to take your test readings? You indicate you noted varying voltage in the speed sensor circuit with throttle changes, but throttle alone should not cause this to happen, particularly if the vehicle is not in motion. I assume you also had the vehicle in gear and the wheels were speeding up and slowing down? Apologies for the simple questions, but assumptions cause lots of problems when trying to troubleshoot things remotely. Assuming the wheels were increasing and decreasing in speed as the sensor voltage was varying this would suggest the sensor is fine. So, if the computer is not receiving this voltage, the only possibility is some kind of wiring problem. Trace the wire and you should find the problem.

The bucking and stalling sounds eerily similar to something I saw once that turned out to be a timing problem. I don't recall exactly what it was now...might have been a jumped tooth or teeth on the timing chain.