P0122 Throttle/Pedal Position Sensor/Switch A Circuit Low

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. P0122 means the signal voltage of sensor A is below its lower limit – electrically meant, not 'throttle closed': typically an open or grounded signal wire or a missing 5 V reference. Limits: Ford below 0.25 V (detected within 1 s), Saab/GM 2011 below 0.3 V for 1 s, Saab cable system below 0.2 V for 5 s. GM treats it as a one-trip fault and switches to reduced engine power; Ford lights the MIL and wrench lamp and continues on the remaining sensor or in 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
• Engine barely responds to the pedal or stalls at idle
• High idle, A/C switched off (cable systems)

Repair estimate

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

What to check first

1. Check 5 V reference
2. Inspect wiring
3. Replace throttle body sensor if faulty

Parts involved

Related codes

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