P0122 Low Input from Throttle Position Sensor/Switch Circuit A

What does the P0122 code mean?

The P0122 trouble code is a generic powertrain code applicable to most vehicles equipped with the OBD-II standard (from 1996 onwards). It indicates that the Powertrain Control Module (PCM) has detected an abnormally low voltage in the Throttle Position Sensor (TPS) “A” circuit. This voltage is typically below the expected minimum threshold, often between 0.17 and 0.20 volts (V).

Role of the Throttle Position Sensor (TPS)

The Throttle Position Sensor (TPS) monitors the opening angle of the throttle valve. It sends an electrical signal to the PCM, which uses this information to regulate the air-fuel mixture and ignition timing. A faulty signal can therefore disrupt engine operation.

Symptoms of the P0122 code

When this code is stored, you may observe one or more of the following symptoms:

• Irregular idle, too low or abnormally high
• Engine hesitation and stumbling
• Surging (RPM fluctuations)
• Weak or no acceleration
• Risk of limp mode

Possible causes of the P0122 code

Several malfunctions can cause the P0122 code to appear:

• Faulty or improperly installed Throttle Position Sensor (TPS)
• Short circuit in the TPS signal circuit (to ground or another wire)
• Wiring problem: open circuit, corroded or loose connector
• Loss of the 5-volt reference voltage
• PCM failure (less common)

Solutions and diagnostic steps

Before replacing parts, perform a methodical check:

1. Visual Inspection: Examine the sensor, its connector, and the wiring for damage, corrosion, or exposed wires.
2. Electrical Check: Using a multimeter, measure the voltage at the TPS (refer to your vehicle’s repair manual for specific values). A voltage below ~0.17 V confirms the problem.
3. Installation Check: If the TPS was recently replaced, ensure it is properly installed and adjusted. On some models (e.g., GM 3.8L engine), the sensor must be rotated to lock into position.
4. Intermittent Test: If the code returns after clearing, look for an intermittent problem (chafing wire, bad ground).

💡 Expert Tip: Improper installation is a common cause. On some engines, the TPS must be inserted and rotated so that its internal tab aligns correctly with the throttle body pins.

Related TPS codes

Other codes related to the Throttle Position Sensor circuit may appear: P0120, P0121, P0123, P0124.