DTC P012300 – Throttle/Pedal Position Sensor A Circuit Low Input.

🚗 DTC P0123 – Throttle/Pedal Position Sensor A Circuit Low Input

Meaning:
The ECU detects very low voltage from the Throttle Position Sensor (TPS) A or Accelerator Pedal Position Sensor (APP) A.
Normal reference voltage: ~0.5V–4.5V.
“Low input” = sensor is stuck below minimum threshold, usually <0.2–0.3V.

✅ Common Causes

1. Faulty TPS/APP Sensor (Sensor A)

Internal short to ground

Sensor not providing correct sweep voltage

2. Wiring Issues

Signal wire shorted to ground

Broken/loose connector

Corrosion, moisture inside connector

Damaged harness near throttle body or pedal

3. 5V Reference Problems

Poor/low reference voltage from ECU

Shared 5V circuit failure (other sensors may also show faults)

4. Ground issue

Weak or open ground circuit for TPS/APP

5. Throttle Body Failure

Motor or internal circuit causing wrong feedback

6. ECU Issue (rare)

🔧 Step-by-Step Diagnosis (Workshop Procedure)

1. Scan Tool Live Data

Check the following:

TPS A (%)

APP A (%)

Throttle Position Voltage A

If reading shows:

0% or 0.00V → sensor signal short to ground or sensor dead

Intermittent drop → loose wiring or connector

2. Inspect Connectors & Wiring

Focus on:

Throttle body connector

Pedal sensor connector

Harness rubbing near engine, battery, footwell

Check for:

Green corrosion

Water intrusion

Loose pins

Broken wires

3. Check Voltage With Multimeter

At TPS/APP Connector:

Pin A – 5V reference
Should read 4.8–5.2V

Pin B – Ground
0V

Pin C – Signal (Sensor A signal)
Should read:

0.5V (closed throttle)

Up to 4.5V (WOT)

If signal is 0V or too low, but 5V and Ground are OK → Replace the sensor.

If 5V missing → Check shared circuits & ECU 5V supply.

If signal wire short to ground → repair wiring.

4. Test Throttle Body (If TPS type inside throttle body)

Remove intake hose

See if throttle platez moves freely by hand

Binding = throttle body replacement

5. Relearn Procedure (After Repair)

Many cars require a Throttle Body Relearn / Idle Relearn after:

Replacing TPS

Replacing throttle body

Disconnecting battery

Use scan tool or manual relearn procedure (varies by brand).

Welcome To Madurai Car Service 💐🙏🏻.