P0123 Code: Throttle/Pedal Position Sensor A Circuit High
The throttle position signal is stuck near 5 volts, so the PCM sees wide open throttle even at idle.
At a glance
Severity: Moderate
- Meaning
- Throttle/Pedal Position Sensor A Circuit High
- System
- Fuel & Air Metering · Powertrain
- Safe to drive?
- With caution
- Typical repair cost
- $20–$850
- DIY difficulty
- Moderate
Wide open throttle normally brings sensor A up to around 4.5 volts; P0123 sets when the signal stays above the upper limit, commonly around 4.7 to 4.9 volts, for a set time. At that point the PCM effectively reads a floored pedal while the throttle may be fully closed. The signal can only get that high if it is connected to the 5-volt reference somehow: the sensor's ground path has opened so the signal floats up to the reference, the signal wire is shorted to the reference or another voltage, moisture is bridging the connector, or the sensor has failed internally. Because the PCM believes the throttle is wide open, side effects are different from a low reading. On cable-throttle engines it may enter clear-flood mode and cut the injectors while cranking, the A/C may be switched off as it would be at full throttle, and the transmission can hold gears far too long.
Can I keep driving? If the engine runs, drive gently and straight to a repair. Drive-by-wire cars usually go into limp mode; on cable-throttle cars harsh or late shifts and an engine that suddenly won't restart are the main risks.
How to read P0123
- P Powertrain
- 0 Generic (SAE)
- 1 Fuel & air metering
- 23 Specific fault
Symptoms
- Check engine light, with limp mode on drive-by-wire vehicles
- Engine cranks but won't start, or starts only when the pedal is slightly pressed (cable throttle)
- Throttle position shows 90–100% in live data with your foot off the pedal
- Automatic holds each gear too long, then shifts hard; kickdown at light throttle
- A/C compressor drops out as if the pedal were floored
- High idle or slow return to idle because deceleration fuel cutoff no longer works properly
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Open in the sensor ground wire or a corroded ground terminal, letting the signal rise to the reference
- Sensor failed internally (worn track shorting wiper to the reference end, or Hall-effect fault)
- Signal wire shorted to the 5-volt reference or another voltage source in the harness
- Water or corrosion bridging terminals inside the connector
- Open in a shared sensor ground, usually with other 'circuit high' codes stored
- Wrong sensor fitted or PCM input fault
Diagnosis step by step
Confirm the reading and note other high codes
Key on, engine off, pedal released: throttle position should read under 1 volt or a low percentage. A reading of 4.7 volts or more confirms the fault. If MAP, intake air temperature or coolant temperature codes for 'high' are also stored, suspect a shared ground wire first.
Tools: OBD-II scanner
Unplug the sensor and watch the signal
Disconnect the throttle sensor with the key on. The PCM pulls the signal low, so the reading should fall to near zero. If it drops, the harness and PCM are fine and the problem is the sensor or its ground; if it stays near 5 volts with the sensor unplugged, the signal wire is shorted to voltage somewhere in the harness.
Tools: OBD-II scanner
Voltage-drop test the sensor ground
With the sensor plugged in and the key on, back-probe the ground terminal and measure to battery negative. It should be below about 0.1 volt. A reading of several volts, or close to 5, means the ground is open, and the sensor is passing the reference straight through to the signal wire.
Tools: Multimeter
Check the connector for moisture and corrosion
Unplug and inspect both halves. Throttle bodies sit low on some engines and catch water from washing or a leaking cowl, and white or green residue between the reference and signal terminals can create a leakage path. Dry, clean and replace the terminals if they are pitted.
Tools: Flashlight, Screwdriver
Test the sensor on a potentiometer design
Measure signal-to-ground resistance while slowly opening the throttle: it should change smoothly across the whole range. A signal that sits close to the reference-to-ground resistance at closed throttle means the wiper is shorting. For Hall-effect sensors, judge by back-probed voltage with a known-good ground.
Tools: Multimeter
Repair, relearn and test-start
Repair the ground or signal wire, or replace the sensor or throttle body, then clear the codes and perform the throttle relearn. Confirm a normal start without touching the pedal, a closed-throttle value under 1 volt and normal shift points on a test drive.
Tools: OBD-II scanner, Screwdriver
Where the parts are
- 1Ignition coil
- 2Spark plug
- 3Fuel injector
- 4Camshaft sensor
- 5Crankshaft sensor
- 6Engine computer (ECM)
- 7Intake manifold
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Clean and dry connector, replace corroded terminals | Yes | $20–$120 |
| Repair sensor ground or shorted signal wire | No | $100–$350 |
| Replace throttle position sensor (cable throttle) | Yes | $90–$260 |
| Replace electronic throttle body | No | $300–$850 |
| Fix cowl or water leak that soaked the connector | Yes | $50–$250 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Notes by brand
Field data
| Jeep | 3 | Cherokee, Compass | |
|---|---|---|---|
| Hyundai | 2 | Azera, Veloster |
Source: NHTSA Complaints API (US government open data), analyzed by DTC mention.
Emissions / smog test impact
Will fail
P0123 keeps the check engine light on, so the car fails an OBD-II emissions inspection. A no-start or limp mode will usually get it fixed before then anyway.
Frequently asked questions
Why won't my engine start with P0123?
Many PCMs have a clear-flood mode: if the throttle reads nearly wide open while cranking, they shut the injectors off to clear a flooded engine. A stuck-high TPS signal triggers that every time, so the engine cranks without fuel. Pressing the pedal slightly doesn't help on every vehicle.
Why did my A/C stop working when this code appeared?
Most PCMs cut the A/C compressor at wide open throttle to give the engine full power. With the signal stuck high, the PCM thinks you are flooring it permanently and keeps the compressor off.
Is a TPS reading high always a bad sensor?
No. A broken ground wire makes a perfectly good sensor output its full reference voltage. That's why the voltage-drop test on the ground terminal comes before replacing parts, especially if other sensor 'high' codes appear at the same time.
Could this make the car accelerate on its own?
On drive-by-wire engines the PCM checks two sensors against each other and against the pedal, and goes into limp mode rather than opening the throttle. On cable-throttle engines the throttle is opened only by the cable, so the wrong signal affects fueling and shifting but can't open the throttle.