Check engine light on with the TPS code. replaced TPS and pig tail and it checked out OK with volt meter. The light still comes back on with the TPS code

here are some things you can check that you haven`t yet

What year,make,model and engine size do you have,you may need a scan tool .

Hello www_ropesmor,

This code P0123 is Throttle position sensor circuit high input.

There four basic reasons for this code.

1. An open or short to ground between the TPS (throttle position sensor) and the ECM (Engine control module).
2. A short to battery voltage between TPS and the ECM.
3. A short between the TPS wires.
4. A faulty TPS.

See below for connector diagrams.

First, with scan tool monitor TPS with throttle closed voltage should be
I f you don't have a scan tool, back probe terminal 1with a volt meter to ground and you will see the voltage as outlined above otherwise follow the steps below.


1.Check to see if there is about 5 volts at the TPS; with engine off key on disconnect the TPS back probe the harness side terminal 3 to ground with a volt meter if there is about 5 volts go to step 2 if about 5 volts if not repair the 5 volt circuit.

2. Probe the harness side terminal 2 to chassis ground with a volt meter, if voltage above .02 repair circuit 2 short to voltage. If voltage is .02 volts or below go to step 3.

3. Probe the harness side terminal 1 to ground with volt meter if below .5 volts go to step 4 if not repair short to battery between TSP harness and ECM connector

4 Turn the ignition off and disconnect the ECM connector . With an ohm meter measure the resistance between the ECM (terminal C18) and TPS ground circuit it should be below 1 ohm. Measure the resistance between the ECM (terminal C8) and TPS signal circuit it should be below 1 ohm. If not repair the open circuit.

After faulty circuit is found and repaired clear code and verify repair.







I hope this helps.

Regards,

netvan

this is an obd2 trouble code table, it can help you understand the meaning of code.
for p0120,
the possible solutions:
If you have access to a scan tool, with KOEO (Key on engine off) observe the TPS voltage. With throttle closed, voltage should be about .45 volts. It should gradually sweep upwards to approximately 4.5 to 5 volts as you depress the throttle. Sometimes only a scope can capture an intermittent glitch in the TPS signal voltage. If you notice a glitch in the TPS sweep voltage, replace the TPS.
NOTE: Some TPS sensors require fine adjustment. If you aren't comfortable with using a DVOM (Digital Volt Ohm meter) to adjust the new TPS, then it's best to take the vehicle to a shop. If the voltage is not .45 volts (+or- .3 volts or so) with the throttle closed or if the reading is "stuck" then unplug the TPS connector. With KOEO check for 5 volts reference voltage present at the connector and a good ground. You can check the signal circuit for continuity by jumping a fused wire between the ground circuit of the TPS connector and the signal circuit. If the TPS reading on the scan tool now reads zero, then replace the TPS. However if that doesn't change the reading to zero, then check for an open or a short on the signal wire and if none is found, suspect a bad PCM. If manipulating the TPS wiring harness causes any change in idle, then suspect bad TPS.

If the bulbs and the fuses are good, check the brake light switch. You might of shorted out the switch when working on the pig tail. Always use a test light or volt meter when installing pig tails. This way you can check for power and ground before hooking a wire up to help prevent shorts. But by what you have said it does sound as if the brake light switch is now bad.

Make sure the switch at the bottom of the brake pedal is not bad. Pull a bulb out of the tail light have someone use a volt meter, while you press the brake, check to see if you have voltage at the pig tail.

no not difficult for weekend mechanic ,just awkard and finger crunching

With the engine and lights off check the other light that is working with an ohm meter and determine which wire is the ground. Then check the same wire on the light that is not working and see if it is grounded. If it isn't, you can probably use the one good ground for both lights. The plug you mentioned is usually called a "pig tail" (I don't know why-doesn't look like one...) and it might still be bad. Or the ground connector is bad. The point is with the lights off the vehicle and apart, use the ohm meter to check out the pig tail and eliminate it.

replace tps switch and adjust it to factory specs.

no you need to get service key reset ok m8