# P0123: Throttle/Pedal Position Sensor/Switch "A" Circuit High **Verdict:** Drive to a shop this week Air intake - Generic OBD-II code, applies to all gasoline cars and light trucks sold in the US since 1996. - **Typical cost:** $100-$900 - **Urgency:** This week - **Most likely:** Failed throttle sensor or open ground wire - **DIY?:** Steps 1-3 ## Quick answer P0123 means the engine computer is seeing a voltage from throttle position sensor "A" that is higher than a working sensor should produce. It usually means a failed sensor, a lost sensor ground or a signal wire touching a voltage source. Many drive-by-wire cars limit power until it is fixed. ## What does P0123 mean? The throttle position sensor reports how far the throttle plate is open. The engine computer feeds it a 5-volt reference and a ground, and the sensor sends back a signal that climbs as the throttle opens. On electronic-throttle cars, two sensors, "A" and "B", live inside the throttle body and are compared constantly, because a wrong reading could make the car accelerate when the driver did not ask. P0123 is a circuit high code. It sets when the "A" signal rises above the highest voltage a working sensor can make, often around 4.5 to 4.9 volts depending on the maker, for more than a short time. A reading pinned near the full 5 volts usually means the sensor's ground circuit is open, the signal wire is shorted to the reference or another voltage, or the sensor has failed inside. Most cars set it on the first trip and many switch to reduced power. ## What are the symptoms of P0123? - Check engine light on, often with a reduced-power or wrench light - Weak acceleration or a speed limit the car will not go past - High or surging idle on some cars - Stalling or rough running when coming to a stop - Shifting that feels harsh or wrong on some automatics ## What causes P0123? Ranked from most to least likely. Check them in this order: the cheap, common causes first. 1. **Failed throttle position sensor "A"** (most common). An internal short or a worn track in the sensor can push its output toward the full reference voltage. It is more likely on high-mileage cars and on older engines with a separate bolt-on sensor that sees years of vibration. If the reference and ground test good at the connector but the signal stays high, suspect the sensor. 2. **Open sensor ground circuit** (common). When the sensor loses its ground, the signal wire floats up toward the 5-volt reference, which the computer reads as circuit high. A broken ground wire, a corroded ground pin or a loose engine ground strap can cause it. Measuring voltage drop across the ground wire with the key on quickly confirms it. 3. **Signal wire shorted to voltage** (common). If the signal wire rubs through and touches the 5-volt reference or another powered wire, the reading jumps high. This happens where harnesses chafe on brackets, after poorly done repairs, or where rodents chew wiring. The fault may come and go with engine movement, so inspect the harness closely along its full length. 4. **Water or corrosion in the connector** (less common). Moisture in the throttle body connector can create a path between terminals, letting reference voltage leak onto the signal pin. It often appears after heavy rain, engine washing or driving through deep water. Drying and cleaning the terminals may clear it, but corroded or loose pins usually need replacing to stay fixed. 5. **Engine computer fault** (rare). An internal computer fault can misread the signal or fail to provide a good sensor ground. It is uncommon and should be considered only after the sensor, wiring, grounds and connector check out. Some makers release software updates for false throttle codes, so a shop may also check for technical service bulletins first. ## How do you diagnose P0123? 1. Read all stored codes and freeze-frame data; pedal or other throttle codes can point to a shared wiring fault. 2. With the key on and engine off, watch throttle position "A" on a scan tool; a reading stuck near 5 volts or 100 percent confirms the code. 3. Unplug the sensor and check that the signal drops to near zero; if it stays high, the wire is shorted to voltage. 4. Measure the 5-volt reference and check the ground circuit for an open or high resistance. 5. Inspect the harness and connector for chafing or water, then replace the sensor or throttle body only if the circuit tests good. ## How do you fix P0123, and what does it cost? | Fix | Typical cost | What it involves | | --- | --- | --- | | Repair wiring, ground or connector | $100-$300 | Restores a lost ground or fixes a wire shorted to voltage. | | Replace a separate throttle position sensor | $100-$300 | Used on older cable-throttle engines with a bolt-on sensor. | | Replace the electronic throttle body | $300-$900 | Drive-by-wire sensors are built in, so the whole unit is replaced and relearned. | ## Is it safe to drive with P0123? > **Drive to a shop this week.** Drive carefully and only as far as a shop, because reduced-power mode can come on suddenly and an unreliable throttle signal can cause stalling or a high idle. If the car surges, stalls often or will not accelerate, have it towed. ## Will P0123 fail an emissions test? P0123 keeps the check engine light on, which fails an OBD-II emissions test in most states. While the throttle is in a fault mode, some monitors may not run at all. After the repair and clearing the code, the readiness monitors read not ready, so drive several days of mixed city and highway trips before testing. ## After the repair: clearing P0123 Clear the code after the repair and run the throttle relearn your car calls for, either a key-on wait or a scan tool procedure. Throttle position "A" should read low at rest and rise smoothly to wide open without spikes. Normal power, a steady idle and no returning code after several drives confirm the fix. ## How to prevent P0123 - Check that engine and body ground straps are tight and clean during routine service. - Keep water away from the throttle body connector when washing the engine bay. - Clip wiring harnesses back in place after any repair so they cannot chafe through. - Deal with rodent problems quickly, since chewed sensor wires often cause throttle circuit codes. ## Codes often seen with P0123 - [P0121](/codes/p0121): Throttle/Pedal Position Sensor/Switch "A" Circuit Range/Performance - [P0122](/codes/p0122): Throttle/Pedal Position Sensor/Switch "A" Circuit Low - [P0505](/codes/p0505): Idle Air Control System - [P0507](/codes/p0507): Idle Air Control System RPM Higher Than Expected - [P0700](/codes/p0700): Transmission Control System (MIL Request) ## Frequently asked questions ### Can I drive with a P0123 code? You can usually drive slowly to a shop, but it is not safe to ignore. The car may enter reduced-power mode, limiting speed and acceleration without warning. If it surges, stalls or cannot keep up with traffic, have it towed instead, and avoid highways until it is repaired. ### What usually causes P0123? A failed throttle position sensor is the most common cause of P0123, followed by an open sensor ground and a signal wire shorted to voltage. Water in the connector is less common. A quick unplug test helps: if the signal drops to zero unplugged, the wiring is probably fine. ### How much does it cost to fix P0123? Most P0123 repairs cost $100 to $900 at an independent shop. Repairing a ground, wire or connector runs about $100 to $300, as does a separate sensor on older engines. A complete electronic throttle body costs about $300 to $900, including the relearn. ### Can I fix P0123 myself? You can check the connector, look for chafed wiring and tighten ground straps yourself. Testing the circuit needs a multimeter and a wiring diagram. Replacing a throttle body is a moderate bolt-on job on many cars, but some need a scan tool relearn afterward to idle correctly. ### Is P0123 the same as P0122? No, they are opposites in the same circuit. P0123 means the sensor "A" voltage is too high, often from a lost ground or a short to voltage. P0122 means the voltage is too low, often from an open signal wire or a short to ground. Both commonly trigger reduced power. ### Can P0123 cause high idle? Yes, on some cars. If the computer stops trusting the throttle sensor, it may hold the throttle at a fixed default opening, which can raise or destabilize the idle. Other cars idle normally but limit acceleration. A high idle that returns to normal after the repair is a good sign. ### Why did P0123 appear after a car wash or rain? Water likely got into the throttle body connector or a damaged section of harness. Moisture can bridge the reference and signal pins, pushing the voltage high. Letting it dry may clear the code, but cleaning or replacing the corroded terminals is the lasting fix if it keeps returning. ### Can a pedal position sensor cause P0123? Usually not directly, because the pedal sensors have their own codes. However, on some cars the pedal and throttle sensors share a reference or ground circuit, so one wiring fault can set codes for both. Several related codes at once point to a shared wire rather than two failed parts. ### Will clearing P0123 fix limp mode? Clearing the code may restore full power briefly, but the code and limp mode return as soon as the computer sees the high voltage again. Only fixing the sensor, wiring or ground solves it. Use the code as a guide, and avoid relying on repeated clearing to get home. ### Is a throttle body covered under warranty? A throttle body is often covered under the powertrain or emissions warranty on newer cars, depending on the maker and mileage. Some makers have issued extended coverage for certain throttle bodies. Check your warranty booklet, and ask a dealer to look up your VIN for special coverage. ## Sources - [SAE J2012: Diagnostic Trouble Code Definitions](https://www.sae.org/standards/content/j2012_201812/) - [EPA: On-Board Diagnostics (OBD)](https://www.epa.gov/state-and-local-transportation/vehicle-emissions-board-diagnostics-obd) ## Other air intake codes - [P0113 Intake Air Temperature Sensor 1 Circuit High (Bank 1)](https://diagxcar.com/codes/p0113) - [P0117 Engine Coolant Temperature Sensor 1 Circuit Low](https://diagxcar.com/codes/p0117) - [P0118 Engine Coolant Temperature Sensor 1 Circuit High](https://diagxcar.com/codes/p0118) - [P0121 Throttle/Pedal Position Sensor/Switch "A" Circuit Range/Performance](https://diagxcar.com/codes/p0121) - [P0122 Throttle/Pedal Position Sensor/Switch "A" Circuit Low](https://diagxcar.com/codes/p0122) - [P0125 Insufficient Coolant Temperature for Closed Loop Fuel Control](https://diagxcar.com/codes/p0125) - [P0128 Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)](https://diagxcar.com/codes/p0128) - [P0130 O2 Sensor Circuit (Bank 1 Sensor 1)](https://diagxcar.com/codes/p0130) - [P0131 O2 Sensor Circuit Low Voltage (Bank 1 Sensor 1)](https://diagxcar.com/codes/p0131) - [P0132 O2 Sensor Circuit High Voltage (Bank 1 Sensor 1)](https://diagxcar.com/codes/p0132) ## Symptoms - [Why does my car lose power when accelerating?](https://diagxcar.com/symptoms/car-loses-power-when-accelerating) - [Why does my car stall while driving?](https://diagxcar.com/symptoms/car-stalls-while-driving) - [Why is my car idling rough?](https://diagxcar.com/symptoms/rough-idle) - [Why does my car jerk when I accelerate?](https://diagxcar.com/symptoms/car-jerks-when-accelerating) --- Source page: https://diagxcar.com/codes/p0123 Updated: 2026-11-03 General information, not a substitute for a qualified mechanic.