P0122
Throttle Position Sensor/Switch A Circuit Low InputP0122 is a generic OBD-II powertrain diagnostic trouble code: Throttle Position Sensor/Switch A Circuit Low Input. It is logged by the engine control unit when the throttle monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P0122 means
DTC P0122 is an SAE generic powertrain code that sets when the Engine Control Module (ECM/PCM) detects a voltage signal from the Throttle Position Sensor (TPS) or Accelerator Pedal Position (APP) sensor on circuit "A" that falls below the manufacturer-defined lower threshold — typically below 0.17–0.20 V when the normal idle reference is approximately 0.45 V and wide-open throttle (WOT) reference is approximately 4.5 V. The ECM continuously monitors this 0–5 V analogue signal to calculate the exact throttle blade angle (cable-driven systems) or pedal demand (drive-by-wire systems) in order to control fuel delivery, ignition timing, and transmission shift points.
Because the signal is below the plausible operating window, the ECM cannot determine actual throttle position and is forced to substitute a default value. On drive-by-wire vehicles this is especially critical: the electronic throttle control (ETC) system may command the throttle to a fixed limp-mode opening (typically 5–15 %) to allow the vehicle to crawl home, while simultaneously disabling cruise control and traction/stability control. The root cause is almost always electrical — a shorted signal wire, corroded connector pin, or a failing sensor wiper — rather than a mechanical fault. P0122 is the low-input sibling of P0123 (high input); if both are stored simultaneously, a broken reference-voltage or ground supply to the sensor is the likely cause.
The code will clear automatically after a set number of warm-up cycles once the fault is no longer present, but the underlying electrical problem must be confirmed repaired; simply clearing it with a scan tool without fixing the cause will result in rapid recurrence and potential safety risk during acceleration.
Common causes
Most-frequently reported root causes when P0122 is logged.
-
1
Faulty TPS or APP sensor (worn resistive track / open wiper contact)
-
2
Shorted or open signal wire between sensor and ECM
-
3
Corroded, loose, or backed-out connector pins at the sensor or ECM harness
-
4
Damaged or chafed wiring harness (short to ground on signal wire)
-
5
Loss of 5 V reference voltage supply to the sensor (broken ref wire or ECM driver fault)
-
6
Poor sensor ground (high resistance on the sensor ground return circuit)
-
7
Low system battery voltage reducing sensor supply below threshold
-
8
Defective ECM (rare — only after all wiring and sensor checks pass)
Symptoms drivers notice
How to diagnose P0122
A typical diagnostic flow when this code is present.
-
1
Connect a scan tool, retrieve all stored codes, and note freeze-frame data; check whether P0123 is also present (suggests reference or ground supply fault rather than sensor alone)
-
2
Perform a visual inspection of the TPS/APP sensor body, connector, and wiring harness for corrosion, bent pins, chafing, or heat damage; reseat connectors and recheck
-
3
With the ignition ON (engine off), use a multimeter to verify 5 V reference and clean sensor ground at the sensor connector; absent or low reference voltage points to the supply circuit or ECM, not the sensor itself
-
4
Back-probe the signal wire and monitor voltage while slowly and smoothly sweeping the throttle or pedal from closed to WOT — voltage should rise linearly from ~0.45 V to ~4.5 V with no dropouts or flat spots
-
5
If signal voltage is flatlined low, disconnect the sensor and recheck signal-wire voltage at the harness side; a short to ground on the wire (rather than the sensor) will hold the line low even with the sensor unplugged
-
6
Replace the TPS/APP sensor if the signal wire and supply circuits test good but the sensor output is still low or erratic; use OEM or OEM-equivalent quality — cheap aftermarket sensors frequently produce out-of-range signals
-
7
Clear codes, perform a full throttle sweep road test, and confirm no recurrence before returning the vehicle
Vehicles where we've handled P0122
Platforms in our catalogue with confirmed P0122 coverage.
Related powertrain codes
- P0120 — Throttle Position Sensor/Switch A Circuit Malfunction
- P0121 — Throttle Position Sensor/Switch A Circuit Range/Performance Problem
- P0123 — Throttle Position Sensor/Switch A Circuit High Input
- P0124 — Throttle Position Sensor/Switch A Circuit Intermittent
- P0220 — Throttle/Pedal Position Sensor/Switch B Circuit Malfunction
- P0221 — Throttle/Pedal Position Sensor/Switch B Circuit Range/Performance
Frequently asked questions
Can I drive with a P0122 code?
Short distances at low speed may be possible if the engine is not in limp mode, but it is not advisable. The ECM cannot accurately determine throttle demand, which creates unpredictable acceleration behaviour and a potential safety hazard. Have the fault diagnosed as soon as possible.
Will replacing the throttle position sensor always fix P0122?
Not always. The sensor is the most common cause, but if the 5 V reference supply is missing or the signal wire is shorted to ground in the harness, a new sensor will not resolve the fault. Always test the circuit voltages before condemning the sensor.
Why is P0122 stored alongside P0123 at the same time?
Simultaneous low and high codes on the same sensor circuit usually indicate a broken reference voltage or sensor ground wire. Without a stable 0 V and 5 V supply, the signal line floats and crosses both thresholds. Inspect the shared supply and ground wires first.
Could a dirty throttle body cause P0122?
A heavily carboned throttle body can mechanically restrict blade movement and prevent the sensor from reaching its expected minimum voltage at rest, but this is an uncommon cause of a hard P0122. Cleaning the throttle body is a worthwhile step during inspection, but check electrical integrity first.
Disabling P0122 in software
RaceTune can permanently disable P0122 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
ECUs with a P0122 disable in our catalogue
Confirmed coverage from our recipe database — we support many more families. Upload your file and our identifier will match it automatically.
- Bosch EDC17C50 verified 1 software version
- Bosch EDC17CP09 verified 1 software version
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
Got P0122 in your scan?
Upload your ECU file — we'll identify the exact software version and confirm whether a disable is available for your car.
Upload your file