What P0122 Means
P0122 means the throttle or accelerator pedal position sensor circuit A is reporting a voltage below the PCM's expected minimum — a low-input fault, as opposed to the range/performance issue flagged by P0121. This typically points to an actual electrical problem: an open circuit, a short to ground, or a sensor that has failed in a way that pulls its output signal down toward zero volts regardless of actual throttle position. Because the PCM can no longer trust this sensor's input at all, most vehicles will immediately default to a safe, low-power limp mode rather than attempt to interpret an unreliable signal. Unlike P0121, which often stems from gradual sensor wear or carbon buildup, P0122 more frequently traces back to a specific wiring fault — a chafed wire, corroded connector pin, or a sensor that has failed outright — making it somewhat more straightforward to isolate with basic electrical testing.
Common Causes
- Open circuit or broken wire in the throttle position sensor signal circuit
- Corroded, damaged, or disconnected throttle position sensor connector
- Short to ground somewhere along the sensor wiring harness
- Failed throttle position sensor with an internally shorted or open signal circuit
- Damaged reference voltage supply to the sensor from the PCM
- Water intrusion into the throttle body connector, common after driving through deep water or heavy rain
Symptoms You Might Notice
- Check Engine Light on, almost always paired with a noticeable loss of power or limp mode
- Engine may be stuck at a fixed, low idle speed regardless of throttle input
- Severely limited acceleration, sometimes to the point the vehicle can barely move under its own power
- Rough or erratic idle immediately after startup
- In some vehicles, the engine may not start at all if the fault is present before startup
What to Check First
- 1
Check the throttle body electrical connector first for corrosion, moisture, or a loose pin, since this is the most common and cheapest fix
- 2
Use a multimeter to check for proper reference voltage (typically around 5 volts) reaching the sensor with the key on, engine off
- 3
Check the signal wire for continuity from the sensor connector back to the PCM, looking for an open circuit or short to ground
- 4
Inspect the wiring harness along its full length for chafing, rodent damage, or exposure to water intrusion, particularly near the engine bay firewall
- 5
If wiring and voltage supply check out, replace the throttle position sensor or full electronic throttle body assembly, since the TPS is rarely separately serviceable on modern vehicles
Frequently Asked Questions
Why is my car stuck in low power mode with this code?
A low-voltage throttle position signal gives the PCM no reliable way to know how much throttle you're actually requesting, so it defaults to a conservative, low-RPM limp mode as a safety measure until the fault is fixed.
Is P0122 dangerous to drive with?
It's not dangerous in the sense of a safety hazard — if anything, the limp mode is a protective response — but the severely reduced power can make the vehicle unsafe to drive in traffic, so it's best towed or driven minimally to a shop rather than used normally.
Can water cause this code?
Yes — water intrusion into the throttle body connector, often after driving through deep puddles or a car wash, is a surprisingly common cause. Drying out and cleaning the connector sometimes resolves it without needing to replace any parts.
Reviewed by Emmanuel Erere, Auto Mechanic. Causes and diagnostic steps checked for workshop accuracy.