Throttle Position Sensor/Switch A Circuit Low Input


This code indicates that the PCM has detected a TPS switch “A” circuit voltage reading that is lower than normal.

Code Set Parameters

Low voltage/resistance variations that exceed 10-percent of the manufacturer’s specified reference voltage (with the throttle in any given position as compared to engine RPMs) will cause a trouble code to be stored and a service engine soon lamp to be illuminated.


Possible symptoms can include black smoke at startup, poor acceleration, a no start condition, misfire at idle, start and stall, and service engine lamp illumination.

Common Causes

Possible causes of this code include a loose TPS electrical connector, faulty TPS circuit wiring, faulty or misadjusted TPS, faulty throttle body, or a faulty PCM. PCM failures are rare.

Common Misdiagnosis

Often the TPS sensor is replaced in error when the electrical connector face has been contaminated with moisture.


  • The PCM receives a variable output voltage reading (usually between .5 to 5.0-volts) from the throttle position sensor
  • This output signal helps the PCM to determine the degree which the throttle body has been opened (and must be opened) in order to achieve the desired RPM level
  • Most modern throttle position sensors are of the non-contact variety and include hall effect sensors, magnetoresistive style sensors, and inductive sensors. Several tools will prove instrumental in successfully diagnosing the condition which caused this code
  • A scanner, a digital volt/ohmmeter, an oscilloscope, and a manufacturer's service manual (or equivalent) will all be very helpful. Begin your diagnosis by visually inspecting all wiring and connectors
  • Look for shorted or burned wiring and replace circuitry and connectors as required
  • If the system wiring, connectors, and components appear to be in normal working order, connect the scanner to the diagnostic connector and record all stored trouble codes and freeze frame data
  • This information can be extremely helpful in diagnosing intermittent conditions that may have contributed to this code being stored
  • After the codes are cleared, operate the vehicle to see if the code returns
  • If the code fails to immediately return, you may have an intermittent condition
  • Intermittent conditions can prove to be quite a challenge to diagnose and in extreme cases may have to be allowed to worsen before a correct diagnosis can be made. To test the throttle position sensor output voltage, measure the signal voltage reading at the connector face as you manually activate the throttle body
  • Watch for sudden jumps in voltage or glitches as the voltage drops
  • Throttle position sensor adjustment is also critical to proper operation (if equipped with an adjustable sensor))
  • If the throttle position sensor checks out, disconnect the connector from the throttle position sensor and any related controllers
  • Perform a continuity and resistance test on all related circuits and repair or replace open or shorted circuits as required
  • Always clear codes and test drive the vehicle to ensure that the repair has been successful. Should all system circuitry and the throttle position sensor prove to be within acceptable specifications, suspect a defective PCM
  • Keep in mind that PCM failure is rare and replacement of such will require reprogramming.