I have a 99 Dodge Ram 5.9L 2WD, I am getting a P0121 as well as my ABS and Brake indicator lights are illuminated, these problems did not occur simultaneously. The P0121 came up a couple of days ago when my wife ran it out of gas. Following that transgression the truck refused to move without stalling. After some time it would move but it sounded as if it was missing. overall very crappy performance.
I performed the voltage sweeps on both sensors and found them to be within the 0-5V range as described in another post.
Earlier today i elected to disconnect the negative terminal from the battery just to see what would happen after 15-20 min. I reconnected the teminal and found that the idle had improved but its still throwing the P0121. What gives?

 

First thing I would do would be to clean IAC, TPS and TB. If that didn't work I'd replace the TPS. If that gets rid of the code but you still have the speedo prob. replace the VSS and go from there.

 

something I forgot to add was that I replaced the TPS few months ago. And what is a TB and VSS ?

 

TB= Throttle Body and VSS is Vehicle Speed Sensor. And what brand TPS did you buy?

 

used the warranty to replace TPS. WHICH SOLVED THE PROBLEM.

 

What brand was it ?

 

BWD

 

BWD is good so I would replace the VSS in top of the rear axle housing.

 

Also running it down that low on fuel it might have picked up junk ,a clogged fuel pump screen/filter. Which obviously won't have anything to do with the ABS problem.