Faulty throttle or pedal position sensor 'D' (internal wear or electrical failure).; Wiring harness damage (open, short, or chafed wires) between the sensor and the ECM.; Corroded or loose electrical connectors at the sensor or ECM.; Mechanical binding or obstruction at the throttle body or accelerator pedal stop.; ECM software issue or failed throttle stop relearn procedure.; Contaminated or dirty throttle body causing the blade to not reach the stop correctly.

DTC codes / P21xx · Fuel and air metering / P2166

P2166Throttle/Pedal Position Sensor 'D' Maximum Stop Performance

Q: What does code P2166 mean?

Throttle/Pedal Position Sensor 'D' Maximum Stop Performance. P2166 indicates that the engine control module (ECM) has detected a performance problem with the maximum stop position of throttle or pedal position sensor 'D'. The ECM expects a specific signal when the accelerator pedal is fully released or the throttle plate is at its mechanical stop, but the sensor 'D' voltage or position reading does not match that expectation. This code is typically set when the sensor's signal is out of range or inconsistent with the other throttle/pedal sensors during the stop-learn or key-on self-test.

P2166 indicates that the engine control module (ECM) has detected a performance problem with the maximum stop position of throttle or pedal position sensor 'D'. The ECM expects a specific signal when the accelerator pedal is fully released or the throttle plate is at its mechanical stop, but the sensor 'D' voltage or position reading does not match that expectation. This code is typically set when the sensor's signal is out of range or inconsistent with the other throttle/pedal sensors during the stop-learn or key-on self-test.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms.
Reduced engine power or limp mode, limiting acceleration.
Poor throttle response or hesitation when pressing the accelerator.
Unexpected idle speed, either too high or too low.
In rare cases, the engine may stall when coming to a stop.

Common causes, most likely first

Faulty throttle or pedal position sensor 'D' (internal wear or electrical failure).
Wiring harness damage (open, short, or chafed wires) between the sensor and the ECM.
Corroded or loose electrical connectors at the sensor or ECM.
Mechanical binding or obstruction at the throttle body or accelerator pedal stop.
ECM software issue or failed throttle stop relearn procedure.
Contaminated or dirty throttle body causing the blade to not reach the stop correctly.

How to diagnose and fix it

Use an OBD-II scanner to read live data for all throttle/pedal position sensors and compare sensor 'D' readings to the others throughout the pedal travel.
Visually inspect the throttle body and accelerator pedal assembly for mechanical binding, debris, or damage at the maximum stop position.
Check the wiring harness and connectors for the sensor 'D' circuit for signs of corrosion, loose pins, or chafed insulation.
Perform a throttle stop relearn or idle relearn procedure according to the manufacturer's instructions using a scan tool.
If live data shows sensor 'D' signal erratic or out of range, test the sensor with a multimeter for resistance and voltage changes through its range.
Replace the faulty throttle or pedal position sensor assembly if testing confirms it is defective.
Clear the diagnostic trouble codes and verify the repair by test-driving the vehicle and confirming the code does not return.

Common misdiagnosis traps for P2166

A dirty throttle body is frequently overlooked; carbon buildup can prevent the throttle plate from reaching its mechanical stop, causing the ECM to set P2166 even when the sensor is good.
Many technicians replace the accelerator pedal assembly unnecessarily when the real problem is a corroded connector or a chafed wire in the harness near the pedal.
The code can be set by a low battery or a voltage drop during cranking, which corrupts the throttle stop learning; always check battery health and perform a relearn before condemning parts.
On some vehicles, P2166 is stored alongside other throttle codes like P2135 or P0121, and replacing only one sensor may not resolve the issue if the correlation between sensors is still off.
After replacing a sensor or throttle body, a proper throttle stop relearn with a capable scan tool is mandatory; skipping this step will cause the code to return immediately.

Can I keep driving with P2166?

You can usually drive the vehicle to a repair shop, but expect reduced engine power and poor throttle response. Avoid aggressive acceleration or high-speed driving, and if the vehicle enters limp mode, pull over safely and seek professional assistance.

Tools that help

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