P0120 medium Severity

P0120: Throttle/Pedal Position Sensor/Switch "A" Circuit Malfunction

Check Engine Light illumination, possible hesitation or poor throttle response, potential limp mode activation

Overview

P0120 is an OBD-II generic powertrain code indicating a malfunction in the Throttle/Pedal Position Sensor/Switch "A" circuit, often related to throttle position sensor voltage issues, wiring faults, or sensor failure

Common Symptoms

  • Check Engine Light (CEL) illuminated
  • Poor idle quality
  • Hesitation during acceleration
  • Possible stalling or reduced engine power

Most Common Causes

Faulty Throttle Position Sensor (TPS) high

TPS failure can send out-of-range voltage causing the PCM to set the code

Damaged or corroded wiring/connectors in TPS circuit high

Broken, frayed, or corroded wires disrupt the sensor signal

Faulty Accelerator Pedal Position (APP) sensor medium

In drive-by-wire systems, APP sensor faults may trigger similar circuit malfunction

Faulty PCM/ECM or software issue low

Less common; suspect after ruling out sensor and wiring faults

Contaminated or dirty throttle body affecting sensor readings medium

Carbon buildup can impact throttle blade position and sensor feedback

Diagnostic Steps

  1. Connect an OBD-II scanner and verify stored codes
    Expected: P0120 and related codes if present
    Interpretation: Confirm the issue is current and note accompanying codes
  2. With key on engine off, monitor TPS voltage using scanner/data stream
    Expected: Voltage near ~0.45–1V at closed throttle and smoothly rising to ~4.5–5V as throttle opens
    Interpretation: Out-of-range or erratic voltage indicates sensor or wiring fault
  3. Visually inspect wiring harness and connectors for corrosion, breaks, or poor connections
    Expected: Clean, intact wiring and solid connector seating
    Interpretation: Damaged wiring requires repair before replacing sensors
  4. Perform a wiggle test on wiring harness while monitoring sensor signal
    Expected: No change in voltage during movement
    Interpretation: Voltage changes during wiggle test suggest wiring/connector issues
  5. If wiring is good, replace the TPS or APP sensor and retest
    Expected: Normal voltage sweep and no P0120 after repair
    Interpretation: Sensor replacement resolves malfunction if confirmed faulty

Repair Solutions

Repair or replace damaged wiring/connectors in sensor circuit medium
Estimated Cost: $50 - $200

Cost varies with extent of wiring repair and labor

Replace Throttle Position Sensor (TPS) medium
Estimated Cost: $100 - $300

Including parts and labor; aftermarket sensor on lower end

Replace Accelerator Pedal Position (APP) sensor if applicable medium
Estimated Cost: $100 - $400

Applicable in drive-by-wire systems

Clean throttle body easy
Estimated Cost: $30 - $100

May improve sensor readings if buildup is affecting operation

PCM/ECM repair or reprogramming hard
Estimated Cost: $300 - $1500

Consider only after all other causes are ruled out

Common Misdiagnoses

Avoid these common diagnostic mistakes:

  • Replacing the TPS when the real issue is wiring/connectors
  • Assuming throttle body needs replacement without checking sensor circuit first
  • Confusing APP sensor faults with TPS circuit issues

Frequently Asked Questions

What is the definition of the P0120 engine code?

Throttle/Pedal Position Sensor/Switch "A" Circuit Malfunction is the standard definition for P0120. This diagnostic code is triggered when the ECU detects a problem in the Sensors.

Is it safe to drive with a P0120 code?

The P0120 code is considered medium severity. Check Engine Light illumination, possible hesitation or poor throttle response, potential limp mode activation

How do I know if I have code P0120?

Common symptoms include: Check Engine Light (CEL) illuminated, Poor idle quality, Hesitation during acceleration. You might also notice the Check Engine Light is on.

Common triggers for the P0120 error

Potential culprits include: Faulty Throttle Position Sensor (TPS), Damaged or corroded wiring/connectors in TPS circuit, Faulty Accelerator Pedal Position (APP) sensor. A proper diagnosis is recommended.

Estimated repair costs for different causes of P0120

It depends on what needs to be fixed. Clean throttle body repairs are cheaper (~$100), while PCM/ECM repair or reprogramming repairs are on the higher end (~$1500).

Is P0120 a generic or manufacturer-specific code?

This is a universal code. You might see P0120 on Ford, Chevrolet, Toyota, Honda, Nissan, or any other OBD-II vehicle.

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