AutoCodes – Mercury – P2123 Mercury

P2123 Mercury Code - Throttle/Pedal Position Sensor/Switch 'D' Circuit High

Quick Answer

The Accelerator Pedal Position (APP) sensor is an input to the Powertrain Control Module (PCM) and used to determine the amount of torque requested by the operator. Common causes include Faulty Accelerator Pedal Position (APP) Sensor, Accelerator Pedal Position (APP) Sensor harness is open or shorted, Accelerator Pedal Position (APP) Sensor circuit poor electrical connection. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means: P2123 Mercury indicates Throttle/Pedal Position Sensor/Switch 'D' Circuit High.
Common causes: Common causes include Faulty Accelerator Pedal Position (APP) Sensor, Accelerator Pedal Position (APP) Sensor harness is open or shorted, Accelerator Pedal Position (APP) Sensor circuit poor electrical connection.
Severity: High - diagnose this code as soon as possible.
Can I drive?: Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

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Code Popularity 1,538

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Intermediate (2 / 3)

What is this?

Table of contents Created and updated by William Orellana on Jul 15, 2020

Description
Possible Causes
How To Fix
Cost to Diagnose
Comments
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Code P2123 Mercury Description

The Accelerator Pedal Position (APP) sensor is an input to the Powertrain Control Module (PCM) and used to determine the amount of torque requested by the operator. There are 2 pedal position signals in the sensor. Both signals, APP and APP2, have a positive slope (increasing angle, increasing voltage), but are offset and increase at different rates. The 2 pedal position signals make sure the PCM receives a correct input even if 1 signal has a concern. The PCM determines if a signal is incorrect by calculating where it should be, inferred from the other signals. If a concern is present with one of the circuits the other input is used. There are 2 reference voltage circuits, 2 signal return circuits, and 2 signal circuits (a total of 6 circuits and pins) between the PCM and the APP sensor assembly. The pedal position signal is converted to pedal travel degrees (rotary angle) by the PCM. The software converts these degrees to counts, which is the input to the torque based strategy. The P2123 code sets when The accelerator pedal position (APP) sensor 1 is out of self-test range high.

OBDII Code P2123 Mercury - Throttle/Pedal Position Sensor/Switch 'D' Circuit High - AutoCodes.com — P2123 Mercury Code - Throttle/Pedal Position Sensor/Switch 'D' Circuit High

What does this mean?

What are the Possible Causes of the DTC P2123 Mercury?

Faulty Accelerator Pedal Position (APP) Sensor
Accelerator Pedal Position (APP) Sensor harness is open or shorted
Accelerator Pedal Position (APP) Sensor circuit poor electrical connection
Faulty Powertrain Control Module (PCM)

How to Fix the DTC P2123 Mercury?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P2123 Mercury code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

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About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.