Working on my mothers 97 Blazer 4.3 , used a code reader and pulled a P0123 TPS high voltage. Replaced the TPS and I still get the P0123, as soon as I clear it it comes back. Pulled plug off and get a P0122 code which seems right. I get 5.15 volts off plug is that to high? Also fuel pump wont run unless jumpered. Will not start but turns over fine. Any help please.

 

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Diagnostic links are at your finger tips...
P0122 - Throttle Position Sensor Circuit Low Voltage
P0123 - Throttle Position Sensor Circuit High Voltage

So you read off the 5V reference line... What are the readings off of the sensor return to the PCM? You need around 0.5V at closed throttle and around 4.5V at wide open throttle with a smooth transition between the two throttle positions. There should be no drop outs in the voltage.

 

I'm reading .56v at throttle closed and 4.45 at full open, seemed smooth through out full range. Ground tested good. Reset code reader, code P0123 came back up, Blazer will not start. Completely at a lose here, every thing looks good but still getting code. Will this fault cause the Blazer not to start, i.e fuel pump not coming on when ignition is turned on? or maybe multiple uncoded faults?

 

The next thing is to test continuity on the wiring to the PCM.