EngineLightCodes
Powertrain code

P0123 Throttle/Pedal Position Sensor/Switch A Circuit High

Severity
Fix soon
Typical repair cost
$20–$500
Do it yourself
Possible, medium
Shop time
0.5–2 hours

Sensor A is, in practice, throttle position sensor 1 at the throttle body; the accelerator pedal has its own codes (P2120 onwards).

How the engine computer detects it

With a cable-operated throttle there is a single potentiometer (about 0.5 V closed to 4.5 V wide open). Electronic throttles have two sensors sharing a 5 V reference and ground, usually running in opposite directions – on GM throttle sensor 1 falls from 3–4 V at idle to below 1 V at full throttle. P0123 means the signal voltage of sensor A is above its upper limit – usually an open sensor ground, which lets the signal float up to the reference, or a signal wire shorted to 5 V or 12 V. Limits: Ford above 4.75 V (within 1 s), Saab/GM 2011 above 4.8 V for 1 s, Saab cable system above 4.96 V for 5 s. Because GM's sensor 1 runs inverted, a high signal there electrically resembles idle, not full throttle. GM sets it after one trip; electronic throttles go into limp mode.

Written from public technical sources and not yet checked by a mechanic. How we write these pages

Symptoms

  • Check engine light, on electronic throttles also wrench lamp
  • Limp mode with reduced power ('Reduced Engine Power') on electronic throttles
  • Raised idle or delayed throttle response
  • Shift problems on automatics

Common causes

  1. Sensor ground (low reference) open or high-resistance Most likely
  2. Signal wire shorted to 5 V or 12 V Possible
  3. Sensor or throttle body faulty Possible
  4. Moisture or corrosion in the connector Possible

How to diagnose P0123

  1. Read every stored code with an OBD-II scanner. If misfire or fuel trim codes are there too, fix those first: they often cause this one.
  2. Inspect the parts involved: throttle position sensor, throttle body, sensor wiring, sensor reference voltage.
  3. Work through the causes above from most to least likely, cheapest checks first.
  4. Clear the code and drive a full drive cycle to confirm the repair held.

Reading the code

P
Powertrain
0
Generic (SAE) code
1
Fuel and air metering
23
Specific fault

Questions drivers ask

Can I drive with code P0123?

Drive gently and only as far as you need to. The engine computer may limit power to protect the engine, so avoid highways and heavy traffic until it's fixed. If the check engine light starts flashing, pull over.

Will my car pass an emissions inspection with P0123?

Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.

Can I fix P0123 myself?

Often yes, with an OBD-II scanner and basic tools. Difficulty: medium. Start with the cheapest checks before replacing expensive parts.

Often reported together

Codes that owners mention in the same NHTSA complaints as P0123. They can point to a shared cause, so it's worth checking them together.

This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.