P0123: Throttle / Pedal Position Sensor "A" Circuit High Input
TL;DR
P0123 = TPS "A" circuit high input. Severity: medium. Top causes: faulty TPS (35%), wiring short to voltage (30%), connector fault (20%), reference/ground fault (15%). Often triggers limp mode.
Can I keep driving with P0123?
IF it drives acceptably → drive briefly to diagnose. IF it surges or is in limp mode → drive minimally; throttle position data is unreliable.
Symptoms
- Check engine light on
- Surging or erratic acceleration
- Reduced-power / limp mode
- Poor throttle response
- Erratic idle
Top causes (ranked by probability)
| Likely cause | Probability | Notes |
|---|---|---|
| Faulty TPS | 35% | |
| Signal wire short to voltage | 30% | |
| Corroded or loose connector | 20% | |
| Poor ground or reference fault | 15% |
What does P0123 mean?
Technical explanation
P0123 sets when the TPS "A" signal voltage stays above the expected range. Causes include a failed sensor, a signal-wire short to voltage (or to the 5 V reference), a poor ground that raises the signal, or a corroded connector. On drive-by-wire systems a high TPS signal usually forces reduced-power (limp) mode.
In simple terms
The throttle position sensor tells the computer how far the throttle is open. P0123 means it’s reading too high — often a wiring short to power, a bad ground, or a faulty sensor. The car may surge, respond poorly to the pedal, and drop into limp mode.
How to diagnose P0123 (step by step)
- Read TPS live data. A reading stuck high (with high voltage) confirms it.
- Inspect wiring for short to voltage. Check the signal circuit for a short to power or to the reference.
- Verify the ground. A poor sensor ground can raise the signal voltage.
- Inspect the connector. Look for corrosion or a loose fit.
- Replace the TPS / throttle body if faulty. If wiring is good, replace the sensor/assembly.
Repair options & cost
- Replace the TPS or throttle body
- Repair the wiring short
- Repair the ground/reference
- Repair the connector
🔧 Doing it yourself? Buy the part: Throttle position (TPS) sensor
| DIY cost | $20–$250 |
|---|---|
| Workshop cost | $120–$500 |
| Repair time | 30–90 minutes |
Costs are local ballpark ranges and vary by region and vehicle.
Tools you’ll need
Scan your car: recommended OBD-II scanners →Vehicle-specific notes
- On many modern cars the TPS is built into the throttle body — you replace the assembly.
- P0123 (high) is the opposite of P0122 (low).
- A poor sensor ground commonly drives the signal high — check grounds.
Common mistakes to avoid
- Replacing the TPS while a wiring short/poor ground is the cause
- Overlooking the ground circuit
- Ignoring a corroded connector
- Skipping the throttle relearn after replacement
Frequently asked questions
What causes a P0123 code?
A faulty TPS, a signal-wire short to voltage, a poor ground, or a corroded connector. On drive-by-wire cars it often forces limp mode.
Is P0123 the same as P0122?
They’re opposites: P0123 is a high TPS signal, P0122 is a low one. Both point to the TPS, its wiring, or the ground/reference.
Can I drive with P0123?
Only short-term. It often triggers limp mode and surging, so diagnose it promptly.
P0123 summary
| Meaning | TPS "A" circuit high input |
|---|---|
| Severity | Medium |
| Safe to drive? | Caution — possible limp mode |
| Top cause | Faulty TPS / wiring (65%) |
| DIY cost | $20–$250 |
| Shop cost | $120–$500 |