DTC P0120 – Throttle/Pedal Position Sensor “A” Circuit.
This code is related to the Throttle Position Sensor (TPS) or Accelerator Pedal Position Sensor (APP) depending on the vehicle.

✅ DTC P0120 – Meaning

P0120 indicates a fault in the Throttle/Pedal Position Sensor A circuit.
The ECM detects that the sensor output is out of expected range.

✅ Common Causes

Throttle Body / TPS Side

Faulty Throttle Position Sensor (TPS)

Throttle body carbon buildup causing the butterfly to stick

Bad throttle body motor

Loose throttle body connector

Damaged TPS wiring (open/short/high resistance)

Poor ground or 5V reference issue

Accelerator Pedal Side

Faulty Accelerator Pedal Position (APP) sensor

Corroded pedal connector

Wiring harness damage under dashboard

ECM Side

Fault in ECM (rare)

✅ Symptoms

Reduced engine power / limp mode

Hesitation on acceleration

High or unstable idle

Poor throttle response

Check Engine Light ON

✅ Step-By-Step Diagnostic Guide

1. Check Live Data (OBD Scanner)

Observe:

TPS A (%)

APP Sensor Voltage (0.5–4.5V typical)
Look for:

Sudden jumps

No movement

Values stuck at 0 or 100%

2. Inspect Throttle Body

Remove air intake duct

Manually check if throttle plate moves smoothly

Clean carbon buildup

Check for water or dirt inside throttle body connector

3. Check Wiring & Connector

Check for:

Broken wires

Chafed insulation

Loose or corroded pins

Shared 5V reference issues (ECT, MAP, TPS share same line on many cars)

Use multimeter:

5V reference present?

Ground good?

Signal wire 0.5–4.5V while pressing pedal?

4. Test Accelerator Pedal Position Sensor

Observe live data for APP1 / APP2

Voltage should increase smoothly as pedal is pressed
If irregular or no change → pedal sensor faulty.

5. Throttle Body Relearn (after repair/cleaning)

Many cars require throttle calibration:

Key ON (no start) for 30 seconds

Or perform scan-tool relearn (better)

6. Replace Parts as Needed

If faulty:

TPS (if separate)

Throttle body assembly (on many modern cars TPS is built-in)

Accelerator pedal sensor

Welcome To Madurai Car Service 💐🙏.