Throttle body and throttle position sensor errors can trigger this problem trouble code of P0123. Otherwise known as Throttle Position Sensor/Switch A Circuit High Input. Your throttle body is responsible for metering the amount of air that enters your 5.7 liter LS1 engine, and your throttle position sensor is responsible for informing your GM ECU of what current position your throttle is open.
When the GM or LS1 ECU sees a value that is higher than what it expects, the ECU will trigger the Malfunction Indicator Lamp (MIL) to notify you of a problem. This can happen a few different ways, either your Throttle Position Sensor (TPS) has failed on you, or there’s a short or break in your TPS wiring. Today I’ll be showing you how to change a LS1 throttle body and service the TPS to correct the issue of P0123 OBDII trouble code.
Whether you are working on a F-body or Corvette, or even a LS1 swap, learning how to change a LS1 throttle body is very easy. Need to test your LS1 TPS while it’s on the vehicle? Check our DIY How To here.
Symptoms of P0123 DTC Trouble Code
- Rough idle
- Bad gas mileage
- Inconsistent throttle response
The LS1 throttle position sensor has an operating range that is not to exceed 4.90 volts at Wide Open Throttle (WOT) and .65 volts with the throttle closed. If your GM or LS1 ECU has triggered your P0123, at some point the TPS has submitted a voltage signal greater than 4.9. This signal wire for your LS1 throttle position sensor can be traced back to the dark blue wire on your LS1 ECU.
For a complete breakdown of the LS1 ECU, complete with wiring diagrams, values and pinouts check our guide here.
The OBDII trouble code of P0123 can also be accompanied by SRS or EVAP codes in your Chevy LS1, as well as other throttle related codes such as; P0120, P0121, P0122, P0123, or P0124. Again, if you need to test the wiring of your LS1 throttle body, check our DIY guide on checking the TPS in the car here.
Before beginning our P0121 OBDII DIY guide on how to change a LS1 throttle body, you will want to disconnect the negative terminal of your battery to prevent any accidents. When working on your car, always keep safety first and foremost in your mind. For our Safety Guideline DIY article, check here.
Also before removing or disconnecting anything, make sure that your battery system and charging system are working correctly. Many OBDII trouble codes can be triggered from a poor battery or lack of charging power. You don’t want to do extra work, so check your battery and have it serviced first.
With your negative terminal on your battery removed, begin our how to change a LS1 throttle body DIY Guide by unplugging your LS1 throttle body. Disconnect all the engine harnesses and connectors, and then locate your throttle body blade.
Depress the LS1 throttle until it’s at Wide Open Throttle, if you are looking for instructions on how to modify your LS1 throttle for 100% Wide Open Throttle, check here.
With the LS1 throttle body opened in this position, rotate and swing your LS1 throttle cable from your throttle body blade. Once your throttle cable end is freed from the throttle body, close the throttle and start removing the three 10mm bolts.
Once you get all three bolts removed, you can pull off your 5.7 liter LS1 throttle body. With the throttle removed, you can now check your LS1 TPS if you wish, or simply replace the throttle body.
Prepare your new LS1 throttle body for it’s new home. Make sure to use the proper gasket and tighten to specification once you have the new LS1 throttle body in place.
The LS1 throttle body carries multiple part numbers, depending on the year, make and model of your donor LS1. The 1998-1999 Chevy and GM F-bodies carried a throttle body with GM part number 17113390 and 17113564. If you own a 00-01 LS1 from a Chevy F-body you will want GM part number 17113647 Throttle body or 17113669. This throttle body is meant for the LS6 intake manifolds as well if you are looking for a How To Install a LS6 intake manifold, check here.
This concludes our how to change a LS1 throttle body DIY article, if you have any questions or comments please feel free to leave them below!