P0122 is a very common OBD-II trouble code that points to a problem with your throttle position sensor (TPS) circuit. When this code sets, your engine computer is seeing a lower-than-expected voltage signal from the TPS, which can cause poor drivability, stalling, or a lack of power. You might notice the check engine light, harsh shifting, or the engine going into “limp” mode. The good news is that P0122 is usually straightforward to diagnose with a basic scan tool, a digital multimeter, and a careful visual inspection of the throttle body and wiring.
What Does P0122 Mean?
P0122 stands for “Throttle/Pedal Position Sensor/Switch A Circuit Low Input.” In plain language, your engine control unit (ECU) is getting a voltage signal from the throttle position sensor that is lower than the expected range for the current throttle opening.
The TPS tells the ECU how far the throttle plate or accelerator pedal is pressed. If the signal drops too low (typically below about 0.2–0.4 volts, depending on the vehicle), the ECU assumes there is a fault in the sensor, wiring, or connector and sets P0122.
Quick Reference
- Code: P0122 – TPS/Accelerator Pedal Position Sensor “A” Circuit Low
- System: Engine fuel and air control
- Severity: Moderate to serious drivability issues
- Common Fixes: TPS replacement, connector repair, wiring repair, throttle body cleaning or replacement
- Tools Needed: OBD-II scanner, digital multimeter, basic hand tools
Real-World Example / Field Notes
In the shop, P0122 often shows up on vehicles with high mileage or after DIY work around the throttle body. A typical case: a customer complains of intermittent stalling when coming to a stop and a sudden loss of power on the highway. The check engine light is on with P0122 stored. A quick inspection reveals a loose TPS connector and green corrosion on the terminals from moisture. After cleaning the connector, repairing a partially broken wire, and clearing the code, the vehicle runs normally with stable TPS readings on the scan tool.
Symptoms of P0122
- Check engine light on: The MIL will illuminate and P0122 will be stored, sometimes with other throttle-related codes.
- Poor acceleration: You may feel sluggish throttle response, hesitation, or a “dead pedal” effect.
- Stalling or rough idle: The engine may stall at stops or idle roughly because the ECU misjudges throttle position.
- Limp mode: The ECU may limit throttle opening and power to protect the engine and transmission.
- Hard starting: Incorrect throttle data can cause long cranking or difficulty starting.
- Transmission shifting issues: On some automatics, incorrect TPS input can cause harsh or delayed shifts.
- Poor fuel economy: The engine may run richer or leaner than intended, wasting fuel.
Common Causes of P0122
Most Common Causes
- Faulty throttle position sensor (TPS): Internal wear, contamination, or failure leads to a consistently low or erratic voltage output.
- Loose or corroded TPS connector: Poor contact at the plug can drop the signal voltage below the ECU’s expected range.
- Damaged wiring to TPS: Chafed, broken, or shorted wires between the TPS and ECU can pull the signal low.
- Incorrect TPS adjustment: On adjustable sensors, improper installation can set the base voltage too low at closed throttle.
- Throttle body issues: Excessive carbon buildup or a sticking throttle plate can cause abnormal sensor readings.
Less Common Causes
- Faulty accelerator pedal position sensor (drive-by-wire): On electronic throttle systems, a bad pedal sensor can mimic TPS faults.
- Low 5V reference from ECU: If the ECU’s reference voltage is low due to another shorted sensor on the same circuit, the TPS signal will also be low.
- ECU internal fault: Rare, but a failing engine control unit can misread a good TPS signal as low.
- Aftermarket modifications: Poorly installed remote starters, alarm systems, or throttle controllers can interfere with TPS wiring.
- Water intrusion: Leaks around the cowl or hood can allow water into harness connectors, causing intermittent low voltage.
Diagnosis: Step-by-Step Guide
You’ll want an OBD-II scanner (preferably one that shows live data and Mode $06), a digital multimeter, and basic hand tools. A wiring diagram for your specific vehicle helps a lot. Always work with the key off when unplugging sensors and be careful not to short pins with your meter probes.
- Confirm the code: Connect your scan tool, read all stored and pending codes, and note any related throttle or pedal position codes. Clear them and see if P0122 returns quickly.
- Check live TPS data: With key on, engine off, watch TPS percentage or voltage. Slowly press the accelerator. It should move smoothly from about 0–10% up to near 100% (or about 0.5V to 4.5V). A stuck low reading supports P0122.
- Inspect the throttle body and connector: Visually check the TPS or throttle body assembly. Look for broken clips, corrosion, oil intrusion, or damaged wiring near the connector.
- Verify reference voltage and ground: With the connector back-probed and key on, confirm you have around 5V on the reference wire and a solid ground on the ground wire. If 5V is missing or low, suspect a shorted sensor or ECU issue.
- Measure TPS signal voltage: Back-probe the signal wire and slowly open the throttle. Voltage should increase smoothly from about 0.4–0.7V at closed throttle to around 4.0–4.8V at wide open. If it stays very low or drops out, the sensor or wiring is faulty.
- Wiggle test the harness: While watching live data or your meter, gently move the harness and connector. If the signal jumps or drops, you likely have an internal wire break or loose terminal.
- Check for shorts to ground: With the connector unplugged and key off, use the multimeter to check resistance from the signal wire to ground. A near-zero reading indicates a short pulling the signal low.
- Inspect related sensors on 5V circuit: If the 5V reference is low, unplug other sensors that share that circuit (MAP, crank, cam, etc.) one at a time to see if the reference voltage returns to normal.
- Evaluate Mode $06 and freeze frame data: Some scan tools show detailed TPS test results and the conditions when the code set. Use this to see if the fault is intermittent or constant.
- Substitute a known-good TPS (if available): On high-mileage vehicles with borderline readings, installing a known-good sensor is often the quickest confirmation.
Pro tip: Don’t just replace the TPS because of P0122. A corroded connector or a damaged wire is just as common and cheaper to fix. Always verify the signal and reference voltages before buying parts.
Possible Fixes & Repair Costs
Most P0122 repairs are straightforward once you find the root cause. Common fixes include replacing the throttle position sensor, repairing or replacing damaged wiring, cleaning or replacing the throttle body, or in rare cases replacing the ECU. Typical repair costs at a professional shop range from about $100–$250 for a simple connector or wiring repair, $150–$400 for TPS or throttle body replacement (parts and labor), and $600+ if an ECU ends up being required. Costs vary by vehicle make, part quality (OEM vs aftermarket), labor rates, and how difficult the throttle assembly is to access.
Can I Still Drive With P0122?
You can usually start and move the vehicle with P0122, but it’s not recommended to keep driving like that. The ECU may limit throttle response, causing poor acceleration and making highway merging or passing unsafe. You may also experience sudden stalling at low speeds or when coming to a stop. Short trips to a repair shop or home are typically okay if the vehicle is still controllable, but avoid long-distance driving or heavy traffic until the issue is diagnosed and repaired.
What Happens If You Ignore P0122?
If you ignore P0122, you risk ongoing drivability problems like stalling, poor acceleration, and unpredictable throttle response. Over time, running with incorrect throttle data can stress the transmission, foul spark plugs, and damage the catalytic converter due to improper fuel mixture. It also leaves you without reliable power when you might need it most, which is a safety concern.
Related Codes
- P0129 – Barometric Pressure Too Low
- P0127 – Intake Air Temperature Too High
- P0126 – Insufficient Coolant Temperature for Stable Operation
- P0125 – Insufficient Coolant Temperature for Closed Loop Fuel Control
- P0124 – Throttle/Pedal Position Sensor/Switch “A” Circuit Intermittent
- P0123 – Throttle/Pedal Position Sensor/Switch “A” Circuit High
- P0121 – Throttle/Pedal Position Sensor/Switch “A” Circuit Range/Performance
- P0120 – Throttle/Pedal Position Sensor/Switch “A” Circuit
- P0119 – Engine Coolant Temperature Circuit Intermittent
- P0116 – Engine Coolant Temperature Circuit Range/Performance
Key Takeaways
- P0122 means the ECU sees a throttle position signal that is too low for normal operation.
- Common causes include a bad TPS, corroded connector, damaged wiring, or low 5V reference.
- Symptoms range from a simple check engine light to stalling, limp mode, and harsh shifting.
- Diagnosis requires a scan tool and multimeter to verify reference, ground, and signal voltages.
- Most repairs are affordable if handled early, typically involving sensor or wiring repair.
- Don’t ignore P0122; it affects safety and can lead to more expensive damage over time.
Vehicles Commonly Affected by P0122
P0122 shows up across many brands because nearly all modern vehicles rely on throttle position sensors. It’s especially common on older GM cars and trucks (Chevrolet, GMC, Buick), Ford models (F-150, Focus, Escape), and Chrysler/Dodge/Jeep vehicles with high mileage. You’ll also see it on Toyota, Honda, Nissan, Hyundai, and Kia models with electronic throttle bodies. Both gasoline and diesel engines can set this code, including sedans, SUVs, pickups, and minivans that use similar TPS or accelerator pedal position systems.
FAQ
Can P0122 be caused by a bad battery or alternator?
A weak battery or failing alternator can cause general voltage issues, but they rarely cause P0122 by themselves. P0122 specifically points to a low signal in the TPS circuit. However, if system voltage is extremely low or unstable, it can aggravate existing sensor or wiring problems.
Is P0122 always the throttle position sensor?
No. While a bad TPS is common, P0122 can also be caused by wiring damage, a corroded connector, a low 5V reference, or in rare cases an ECU fault. That’s why it’s important to test the circuit with a multimeter and not just throw parts at the problem.
How do I know if my TPS needs to be replaced?
If the TPS signal voltage is stuck low, drops out when you move the throttle, or shows dead spots on a scan tool graph, the sensor is likely bad. Combined with P0122 and a good 5V reference and ground, that’s strong evidence the TPS itself needs replacement.
Can I clean the throttle body to fix P0122?
<pCleaning a dirty throttle body can help if the plate is sticking or not returning fully to the closed position, which can confuse the TPS reading. However, cleaning alone won’t fix an internal TPS failure or a wiring issue. It’s a good maintenance step but not a guaranteed cure for P0122.
How urgent is it to fix P0122?
You should address P0122 as soon as possible. While the car may still run, you’re at risk of stalling, poor throttle response, and unsafe driving conditions. Fixing it early also helps prevent secondary damage to the transmission, catalytic converter, and other components.