Technical Definition
Code P2125 indicates a problem with the performance or signal range in the throttle position sensor (TPS) circuit. This sensor measures the throttle opening angle and sends a signal to the PCM (Powertrain Control Module) to regulate fuel injection and ignition. An incorrect signal disrupts the air-fuel mixture, affecting engine performance.
Common Symptoms
- Check engine light on (MIL).
- Unstable idle or vibrations.
- Misfires during acceleration or at constant speed.
- Hard starting or engine stalling.
- Noticeable power loss.
Main Causes
| Category | Details |
|---|---|
| Mechanical issues | Sticking or binding throttle return spring. |
| Electrical failures | Damaged wiring, corroded MAP/TPS connectors, short circuit. |
| Faulty TPS sensor | Inconsistent signal or voltage range interruption. |
| Failing PCM | Incorrect interpretation of TPS signal. |
Diagnostic Steps
1. Check TPS Voltage (KOEO)
- Tool required: Digital multimeter (DVOM) or oscilloscope.
- Procedure:
- Turn ignition on (without starting the engine).
- Measure voltage between the signal wire and ground.
- Expected values:
- Throttle closed: ~0.45 V (tolerance ±0.3 V).
- Throttle open: ~4.5–5 V.
2. Test Electrical Circuit
- Continuity: Check for no breaks between TPS and PCM.
- 5V Reference: With TPS connector unplugged, ensure reference wire provides 5V.
- Ground: Test ground connection with ohmmeter (< 1 Ω).
3. Inspect Wiring and Connectors
- Chafing/Corrosion: Look for frayed wires or greenish connectors.
- Harness manipulation: Gently shake TPS wiring during measurement to detect intermittent issues.
4. Diagnose PCM
- Signal simulation: Short signal wire to ground. If voltage remains stuck, suspect faulty PCM.
Solutions and Costs
| Problem | Solution | Estimated Cost (€) |
|---|---|---|
| Faulty TPS sensor | Replace and recalibrate (e.g., Bosch 0280126004). | 50–150 |
| Damaged wiring | Repair harness or replace connector. | 30–200 |
| Throttle cleaning | Remove and clean with specific degreaser. | 20–80 |
| PCM replacement | Reprogramming or exchange at dealership. | 500–1,500 |
Best Practices
- TPS calibration: After replacement, adjust voltage to 0.45 V with throttle closed (follow manufacturer’s manual).
- Use an oscilloscope: To capture intermittent issues not visible with a multimeter.
FAQ
Q: Can I drive with a P2125 code?
A: Yes, but avoid sudden acceleration. The engine may stall or consume more fuel.
Q: The code returns after replacing the TPS. Why?
A: Check wiring or PCM. Residual short circuit or incorrect calibration may persist.