P0123 Throttle/Pedal Position Sensor/Switch A Circuit High

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

Likely causes

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

Repair estimate

Typical range across vehicles; the real cost depends on what the testing finds.

What to check first

1. Check ground circuit
2. Inspect wiring
3. Replace sensor if faulty

Parts involved

Related codes

References: law.cornell.edu, gsi.ext.gm.com, newtonnet.co.uk, saabwisonline.com.