Worn or contaminated accelerator pedal position sensor tracks inside the pedal assembly.; Corroded, loose, or damaged electrical connector at the accelerator pedal sensor.; Chafed or broken wiring in the harness between the pedal sensor and the engine control module.; Internal fault in the engine control module affecting the sensor reference voltage or signal processing.; Water intrusion or debris contamination in the pedal sensor housing.; Aftermarket floor mats or objects obstructing full pedal travel, causing implausible signal correlation.; Poor ground connection shared by the pedal sensor circuit, leading to voltage drop under load.

DTC codes / Mercedes-Benz codes / P1222

P1222 · Mercedes-BenzIFI Accelerator Pedal Position Sensor R252

Q: What does code P1222 mean?

IFI Accelerator Pedal Position Sensor R252. P1222 on Mercedes-Benz vehicles indicates that the engine control module has detected an implausible or missing signal from the accelerator pedal position sensor circuit, specifically the R252 sensor element. The computer compares the two redundant pedal sensor signals and sets this code when their relationship falls outside the expected range, which can affect throttle response and limp-home mode activation.

P1222 on Mercedes-Benz vehicles indicates that the engine control module has detected an implausible or missing signal from the accelerator pedal position sensor circuit, specifically the R252 sensor element. The computer compares the two redundant pedal sensor signals and sets this code when their relationship falls outside the expected range, which can affect throttle response and limp-home mode activation.

SystemPowertrain

Code typeMercedes-Benz specific

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering (injector circuits)

Symptoms you may notice

The electronic throttle control warning light or check engine light illuminates on the dashboard.
The engine may enter limp-home mode, limiting power and engine speed to a fast idle.
Acceleration may feel delayed, uneven, or unresponsive when pressing the pedal.
The transmission may shift harshly or refuse to downshift under acceleration.
Often no symptoms besides the warning light, especially if the fault is intermittent.
In some cases, the engine may stall or refuse to start after the fault becomes permanent.

Common causes, most likely first

Worn or contaminated accelerator pedal position sensor tracks inside the pedal assembly.
Corroded, loose, or damaged electrical connector at the accelerator pedal sensor.
Chafed or broken wiring in the harness between the pedal sensor and the engine control module.
Internal fault in the engine control module affecting the sensor reference voltage or signal processing.
Water intrusion or debris contamination in the pedal sensor housing.
Aftermarket floor mats or objects obstructing full pedal travel, causing implausible signal correlation.
Poor ground connection shared by the pedal sensor circuit, leading to voltage drop under load.

How to diagnose and fix it

Read all stored and pending fault codes with a Mercedes-Benz-compatible scan tool and record freeze-frame data for P1222.
Inspect the accelerator pedal assembly for physical damage, debris, or aftermarket floor mat interference, and verify full pedal travel.
Disconnect the pedal sensor connector and check for corrosion, bent pins, or loose terminals; clean and reseat as needed.
Back-probe the sensor connector and measure reference voltage, signal voltage, and ground integrity while slowly sweeping the pedal through its range.
Compare the two redundant pedal sensor signal voltages on a live data stream to confirm whether one track is erratic or out of correlation.
Check the wiring harness between the pedal sensor and the engine control module for continuity, shorts to ground, and shorts to voltage.
If wiring and connectors are sound, replace the accelerator pedal assembly with the integrated sensor and clear the code to verify the repair.

What Mercedes Techs Check Before Replacing the Pedal

A common misdiagnosis is replacing the accelerator pedal assembly when the real fault is a corroded connector or chafed wire near the pedal bracket, so always perform a voltage drop test on the ground circuit first.
The R252 designation refers to a specific sensor element within the pedal assembly, and on some Mercedes models the pedal must be replaced as a complete unit because the sensor is not serviced separately.
Intermittent P1222 codes often appear after heavy rain or floor cleaning, pointing to water intrusion at the pedal connector rather than a failed sensor.
Aftermarket floor mats that slide forward and restrict pedal travel can set this code by causing the two sensor signals to fall out of correlation, so check mat position before any parts replacement.
A weak battery or poor charging system voltage can cause the engine control module to misread the pedal sensor signals, so verify battery and charging system health before condemning the pedal.

Can I keep driving with P1222?

You can usually drive the vehicle to a workshop if the car remains in limp-home mode, but avoid heavy traffic and high-speed roads because throttle response may be unpredictable. If the engine stalls or the pedal becomes completely unresponsive, stop driving and arrange a tow.

Tools that help

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Guidance is general and written for Mercedes-Benz vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.