DTC P012100 – Throttle/Pedal Position Sensor A Circuit Range/Performance.

🔧 DTC P0121 – TPS/Pedal Position Sensor A Range/Performance

📌 Meaning

The engine control module (ECM) detects that the Throttle Position Sensor (TPS) A or Accelerator Pedal Position Sensor (APP) A is giving a signal outside the expected range or not matching actual throttle angle.

This usually means:

Sensor reading jumps

Signal too high/low but not open/short

Sensor not synchronized with actual throttle movement
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🔍 Possible Causes

Sensor / Electronics

Faulty TPS sensor (at throttle body)

Faulty APP sensor (at accelerator pedal)

Contaminated / carbon-filled throttle body

Bad sensor ground or 5V reference

Loose or corroded sensor connector

Wiring damage (short, high resistance)

Mechanical

Sticky throttle blade

Throttle body motor weak or binding

ECM Related

ECM internal fault (rare)

Throttle body adaptation not performed after service

🧰 Step-by-Step Diagnosis (Mechanic Level)

1. Scan Data Check (Vital)

Look at:

TPS A (% or voltage)

TPS B

APP A

APP B

Normal values:

TPS A at idle: 0.5–1.0 V

TPS A at WOT: 4.0–4.5 V

APP A idle: 0.4–0.9 V

APP A full press: 3.5–4.5 V

Red flag signs:

Sudden jumps

Stuck value

Not increasing smoothly

A & B not matching (should track together)

2. Throttle Body Inspection

Remove intake hose

Manually check if throttle plate is smooth

Look for heavy carbon deposits

Clean throttle body if necessary
(don’t push throttle plate with force on some electronic throttle bodies)

3. Wiring & Connector Check

Inspect:

Green corrosion inside pins

Broken locking tab

Oil contamination near throttle body

Perform:

5V reference check (should be 4.9–5.1V)

Ground continuity check

Signal voltage sweep test (use multimeter/scan tool)

4. Accelerator Pedal Sensor Check

If TPS values are correct but APP values are erratic → replace/apply repair on pedal position sensor.

5. Throttle Body Adaptation (Important After Cleaning or Replacement)

Many cars require:

1. Key ON (10–30 seconds)

2. Key OFF (10 second)

3. Some models require adaptation via scan tool
If not done → P0121 will return.

🔧 Most Common Fixes in Workshops

Throttle body cleaning

Replace throttle position sensor (if separately available)

Replace complete throttle body (common on newer cars)

Repair damaged wiring / connectors

Replace accelerator pedal assembly (if APP faulty)

Perform throttle body adaptation

💡 Quick Technician Tips

Compare TPS A vs TPS B → mismatch indicates bad throttle body.

Compare APP A vs APP B → mismatch indicates bad pedal sensor.

If the voltage drops when shaking the connector → loose pin.

If all readings are perfect but code persists → check for ECM updates (very rare).

Welcome To Madurai Car Service 💐🙏🏻.