Is P0122 the same as P0121?

No — different failure modes. P0121 is a 'range/performance' code: the sensor reads in-range but doesn't match what the PCM expects (usually throttle body contamination). P0122 is a hard electrical failure: the sensor signal is pegged near zero, which means the circuit is broken, shorted to ground, or the sensor element has failed internally. P0121 is often fixed with throttle body cleaning. P0122 is usually a wiring repair or throttle body replacement. If you see both codes together, diagnose P0122 first — fixing the electrical fault usually clears both.

Can I drive with P0122?

Drive it home or to a shop, yes. Continue driving it normally, no. The PCM has put the throttle into a hard limp mode that caps your RPM in the 1,500-2,500 range, which is fine for surface streets but dangerous on highways. You won't be able to accelerate to merge safely, won't be able to pass, and won't be able to climb hills at normal speeds. P0122 also doesn't tend to clear on its own — the failure is electrical and persistent — so the limp mode stays until you fix it.

Why does P0122 show up right after a repair?

Throttle body connectors and the surrounding wiring are easy to disturb during under-hood work, and the locking tab on the connector can be damaged or partially released without obvious visible signs. If P0122 appeared right after intake manifold service, air filter housing work, EGR work, or any wrenching in the throttle body area, the first step is pulling and reseating that connector. Inspect for pushed-back pins, missing locking tab, or pinched wires routing against something hot or sharp. This is the leading cause of post-repair P0122 codes.

Can I test the TPS circuit at home?

Yes, with a multimeter and the wiring pinout for your platform. Three quick checks: 1) With sensor disconnected and key on, measure voltage between the reference pin (harness side) and chassis ground — should be 5V. 2) Measure continuity between the ground pin (harness side) and chassis ground — should be near zero ohms. 3) Reconnect sensor, use a scan tool to watch the TPS signal voltage while slowly opening the throttle plate by hand. Stuck at 0V with key on confirms the failure pattern. If 5V reference is present and ground is good but the signal is pegged at 0V when connected, the sensor (or throttle body) is the failure point.

OBD-II trouble code

P0122: Throttle/Pedal Position Sensor 'A' Circuit Low Input

The throttle position sensor signal is pegged near zero volts no matter where the pedal is. This is an electrical fault — usually an open ground, broken signal wire, or shorted-internal sensor — not a contamination issue like P0121.

Quick facts

System: Powertrain
Category: Throttle / Idle
Severity: High severity
Drivable: Usually safe to drive short-term
Repair cost range: $100 – $700
DIY difficulty: Intermediate DIY

What does P0122 mean?

P0122 sets when the PCM sees the throttle position sensor (TPS) signal sitting at or near the lower limit of its voltage range — typically below 0.2-0.3V — regardless of throttle plate position. On a healthy TPS, signal voltage rises smoothly from about 0.5V at closed throttle to about 4.5V at wide-open throttle. When the signal drops below the lower threshold and stays there, the PCM concludes the circuit has shorted to ground, opened, or that the sensor has failed in a way that drags the output low, and P0122 sets.

This is the diagnostic opposite of P0123 (signal pegged high). Both codes indicate a hard electrical failure rather than a drift or wear issue — the sensor isn't lying subtly; it's broken or disconnected. The PCM responds by disregarding the TPS signal and falling back to a limp strategy: throttle is held near idle position, RPM is capped (commonly at 1,500-2,500), and most platforms show a 'Reduced Engine Power' message. The vehicle moves but it doesn't accelerate normally.

The diagnostic path is mostly electrical. Three main causes account for the majority of P0122 codes: open signal wire (broken or disconnected), open or shorted-to-ground reference voltage to the TPS, and a failed TPS element shorted internally to ground. On most electronic throttle bodies, the TPS is integrated into the throttle body assembly and isn't serviceable separately — confirming the TPS is the failure point usually means replacing the whole throttle body, not just a sensor.

P0122 frequently appears after physical events that could disturb wiring: recent throttle body service, an under-hood repair near the throttle body, or rodent damage to the harness. If the code appeared right after another repair, suspect a pinched or partially-disconnected harness first before condemning the throttle body itself.

Common causes

Broken or disconnected TPS signal wire between the sensor and the PCM
Open or shorted-to-ground 5V reference voltage to the TPS
Failed TPS element internally shorted to ground
Corroded, water-intruded, or pushed-back pin in the throttle body connector
Damaged connector locking tab causing intermittent disconnection
Rodent damage to the harness (common in vehicles parked outside or unused for periods)
Wire pinched or disconnected during a recent under-hood repair
Failed PCM input circuit (rare)

Symptoms

Check Engine Light on, often immediately at key-on
'Reduced Engine Power' warning on the dash
Hard limp mode — RPM strictly capped, often near 1,500
Engine starts but won't accelerate beyond idle in some cases
Throttle pedal feels completely unresponsive past a small initial range
May stall when coming to a stop
Rough or unstable idle

Diagnostic steps

1.Pull all codes. P0122 alone is a TPS-side failure. P0122 with P2122 or P2127 may indicate a more systemic wiring issue.
2.Inspect the throttle body connector first — disconnect it, look for corrosion, water, pushed-back pins, or damaged locking tab. Many P0122 codes resolve at the connector.
3.With the sensor disconnected, key on, measure voltage between the TPS signal pin and ground at the harness side. Should see 5V reference. If 0V, the reference wire is broken or shorted. If 5V is present, the reference is fine and the issue is downstream.
4.Verify ground continuity from the TPS ground pin (harness side) to chassis ground. Open here is a common cause.
5.Reconnect the sensor and watch TPS signal on a scan tool. If voltage stays near 0 with the engine off and key on, the sensor is grounded internally or the signal wire is open.
6.Backprobe the signal wire at the connector — if you see 0V there but 5V reference is present, the sensor itself is the failure (replace throttle body on most modern vehicles).
7.After any repair, perform the platform-specific throttle relearn procedure.

Repair cost

$100 – $700

Low end is a connector cleanup, pin repair, or harness wire repair when the diagnosis points at wiring — under $150 with diagnostic time. Mid-range $300-500 is throttle body replacement on mainstream platforms (Ford, GM, Toyota, Honda) since the TPS is usually integrated and not serviceable separately. Upper end is $500-700 for luxury platform throttle body replacement (BMW, Audi, Mercedes). Add $50-100 if a relearn requires shop scan tool time. Wiring/connector repairs are difficult to estimate up front because they depend on how much harness has to be opened to find the bad section.

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DIY vs shop

This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.