P0122: Throttle / Pedal Position Sensor "A" Circuit Low Input
TL;DR
P0122 = TPS "A" circuit low input. Severity: medium. Top causes: faulty TPS (35%), wiring short to ground/open (30%), connector fault (20%), reference/ground fault (15%). Often triggers limp mode.
Can I keep driving with P0122?
IF it drives acceptably → drive briefly to diagnose. IF it’s in limp mode or throttle response is poor → drive minimally; throttle position data is unreliable.
Symptoms
- Check engine light on
- Poor throttle response
- Reduced-power / limp mode
- Hesitation
- Erratic or stuck idle
Top causes (ranked by probability)
| Likely cause | Probability | Notes |
|---|---|---|
| Faulty TPS | 35% | |
| Signal wire short to ground or open circuit | 30% | |
| Corroded or loose connector | 20% | |
| Reference voltage or ground fault | 15% |
What does P0122 mean?
Technical explanation
P0122 sets when the TPS "A" signal voltage stays below the expected range. Causes include a failed sensor, a signal-wire short to ground, an open signal/reference circuit, or a corroded connector. On drive-by-wire systems a low TPS signal usually forces reduced-power (limp) mode because the ECM can’t trust throttle position.
In simple terms
The throttle position sensor tells the computer how far the throttle is open. P0122 means it’s reading too low — often a wiring short to ground, an open circuit, or a bad sensor. The car may have poor throttle response and drop into limp mode.
How to diagnose P0122 (step by step)
- Read TPS live data. A reading stuck low (with low voltage) confirms it.
- Inspect wiring for short/open. Check the signal circuit for a short to ground or an open.
- Verify reference and ground. Confirm 5 V reference and a good ground at the connector.
- 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/open)
- Repair the connector
- Fix the reference/ground
🔧 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.
- P0122 (low) is the opposite of P0123 (high).
- A relearn may be needed after replacing the throttle body.
Common mistakes to avoid
- Replacing the TPS while a wiring short/open is the cause
- Overlooking the reference/ground
- Ignoring a corroded connector
- Skipping the throttle relearn after replacement
Frequently asked questions
What causes a P0122 code?
A faulty TPS, a signal-wire short to ground or open circuit, a corroded connector, or a reference/ground fault. On drive-by-wire cars it often forces limp mode.
Is P0122 the same as P0123?
They’re opposites: P0122 is a low TPS signal, P0123 is a high one. Both point to the TPS, its wiring, or the reference/ground.
Can I drive with P0122?
Only short-term. It often triggers limp mode and poor throttle response, so diagnose it promptly.
P0122 summary
| Meaning | TPS "A" circuit low input |
|---|---|
| Severity | Medium |
| Safe to drive? | Caution — possible limp mode |
| Top cause | Faulty TPS / wiring (65%) |
| DIY cost | $20–$250 |
| Shop cost | $120–$500 |