P0122 Throttle Position Sensor/Switch "A" Circuit Low Input

on

P0122 Throttle Position Sensor/Switch "A" Circuit Low Input

What Does Code P0122 Mean?

Diagnostic Trouble Code P0122 indicates that the Engine Control Module (ECM/PCM) has detected an abnormally low voltage signal from the Throttle Position Sensor (TPS) "A" circuit. The voltage is below the manufacturer's specified threshold, usually because of a short to ground, a faulty TPS, poor electrical connections, or damaged wiring.

Symptoms

  • Check Engine Light (MIL) illuminated
  • Reduced engine power (Limp Mode)
  • Poor throttle response
  • Slow or no acceleration
  • Engine hesitation
  • Rough idle
  • Possible engine stalling

Possible Causes

  • Faulty Throttle Position Sensor (TPS)
  • Short to ground in the TPS signal wire
  • Damaged or pinched wiring harness
  • Loose or corroded electrical connector
  • Poor sensor ground
  • Faulty electronic throttle body
  • ECM failure (rare)

Typical Circuit

ECM (5V Reference)
        │
        ├────────────► TPS Sensor A
        │
Ground ─┘
        │
Signal ─────────────► ECM

Signal Flow

Accelerator Pedal
        │
        ▼
Throttle Body
        │
TPS Sensor A
        │
Low Voltage Signal
        ▼
ECM
        │
Throttle Control
Fuel Injection
Ignition Timing

How to Diagnose

1. Visual Inspection

  • Inspect the TPS connector for corrosion or loose terminals.
  • Check the wiring harness for damage, melted insulation, or contact with metal components.
  • Inspect the throttle body for binding or contamination.

2. Live Data Test (Autel)

  • Open Diagnosis → Engine → Live Data.
  • Monitor Throttle Position Sensor A.
  • With the ignition ON, observe the throttle position while slowly pressing the accelerator pedal.
  • If the reading remains fixed near 0% or changes very little despite throttle movement, the ECM is receiving a low TPS signal.
  • Compare TPS A with TPS B (if equipped). Large differences indicate a sensor or circuit fault.

3. Multimeter Test

  • Verify the 5V reference voltage.
  • Check sensor ground continuity.
  • Measure TPS output voltage while opening the throttle.
  • Inspect the signal wire for a short to ground.

4. Smoke Test (If Applicable)

A smoke test is not normally required for P0122 because it is an electrical circuit fault. However, if unstable idle or lean condition codes are also present, inspect the intake system for vacuum leaks.

Common Repairs

  • Replace the faulty TPS sensor.
  • Replace the electronic throttle body if the TPS is integrated.
  • Repair shorted or damaged wiring.
  • Repair poor connector terminal contact.
  • Perform a throttle relearn procedure if required.
  • Clear the DTC and verify normal throttle operation.

Severity

High. P0122 commonly causes limp mode, poor acceleration, and unsafe driving conditions due to reduced throttle control.

Important Note

TPS voltage ranges, connector pinouts, wiring colors, and throttle relearn procedures vary by manufacturer. Always consult the factory service information for the specific vehicle before performing diagnostics or repairs.

Comments

Post a Comment