P2122 Code: Throttle/Pedal Position Sensor/Switch D Circuit Low Input

What the P2122 code means

The gas pedal carries two independent sensors, usually identified as D and E. D is the main signal, the one the computer uses as its reference, and E exists to verify it.

The P2122 code is stored when the signal from sensor D falls below the expected minimum, typically below 0.2 volts for a sustained time. At rest the signal never reaches zero, precisely so the computer can tell a released pedal from a cut circuit.

There is a diagnostic detail worth using. If this code shows up alone, the problem is in the circuit of sensor D and only that one. If it shows up with P2127, which covers sensor E, then both signals are down, and that points to something they share: the common ground, the reference supply or the pedal connector itself.

That reading saves a lot of work. Two sensors failing at once are almost never two separate failures. They are one failure in the shared element.

It helps to understand why the resting signal never drops to zero. If the manufacturer had calibrated the released pedal as zero volts, a cut wire would produce exactly the same reading, and the computer could not tell a driver with a foot off the pedal from a broken circuit. Leaving about half a volt at rest solves that ambiguity: any value below it can only mean a fault. It is the same principle that almost every critical sensor in the vehicle follows.

It is worth knowing about a check that takes one minute: look under the pedal. A shifted floor mat, a bottle or a loose object can keep the pedal slightly pressed or keep it from returning all the way to rest, and the system sees that as a signal outside what is expected. It is a trivial cause but a real one, especially after cleaning the interior or changing floor mats.

P2122 code symptoms

• Limp mode with very limited power.
• Check engine light on and the electronic throttle warning symbol.
• The engine does not respond to the pedal.
• Rough idle, or an engine that stalls.
• Pedal reading at zero on the scan tool with your foot off.
• Hard starting.
• The symptom appears suddenly while driving.
• The pedal does not return all the way to its rest position.

Likely causes of the P2122 code

1. Signal wire cut or shorted to ground.
2. Pedal connector with backed-out pins or moisture.
3. Open common pedal ground, which affects both signals at once.
4. Missing five volt reference supply.
5. Pedal sensor failed internally.
6. Chafed wiring between the pedal and the computer.
7. Liquid that got into the pedal.
8. Damaged input stage in the computer. Uncommon.
9. Shifted floor mat or an object under the pedal, which keeps it from returning fully to rest.

How to diagnose the P2122 code step by step

1. Check whether P2127 is also stored. If both signals are down, look for the shared element: ground, supply or connector.
2. Watch both signals in live data. If only one reads zero, the problem is limited to that circuit.
3. Verify the five volt reference at the pedal connector.
4. Measure the voltage on the signal wire with the sensor unplugged. If it stays at zero, the wire is cut or shorted to ground.
5. Check the common ground by measuring its voltage drop.
6. Inspect the pedal connector by unplugging it and seating it firmly again.
7. Wiggle the harness with the key on while watching the reading.
8. Check for spills around the pedal area.
9. Look under the pedal before anything else. A shifted floor mat or a loose object keeps the pedal from returning fully and alters the signal.

How to fix the P2122 code

• Repair the common pedal ground if its voltage drop is high, because it affects both signals at once.
• Fix the cut or grounded signal wire with solder and heat-shrink tubing.
• Restore the reference supply by finding the short circuit that is loading it.
• Clean the connector and replace terminals with backed-out pins.
• Replace the pedal sensor if the circuit is good and it still gives no signal.
• Dry the area if liquid got in, and check the condition of the floor mats.
• Remove any objects under the pedal and secure the floor mat, then check that the pedal returns fully to rest.

After the repair, run the throttle relearn if the vehicle requires it and check that both signals travel their range in step with each other.

Technical reference data

• Typical sensor D signal at rest: between 0.5 and 0.9 volts, never zero.
• Threshold that sets the code: below 0.2 volts for a sustained time.
• Reference voltage: 5 volts, shared with other sensors in many systems.
• Allowable voltage drop on the ground: below 0.2 volts.
• P2123 is the opposite code: signal too high.
• P2127 covers the second signal of the same pedal.
• The pedal must return fully to its rest position with nothing in the way.

Brand-specific notes

The combination of codes is the most useful information here. A P2122 alone points to its own circuit, and a P2122 together with a P2127 points to the common ground, the supply or the pedal connector. Reading that combination before you measure saves a lot of time.

Before you order a pedal, unplug its connector and plug it back in firmly. A poorly seated connector after work inside the vehicle explains a notable share of these cases.

Frequently asked questions about P2122