P1125 – Accelerator Pedal Position Sensor Fault (GM)

By Reinier (Contact Me)
Last Updated 2021-03-24
Automobile Repair Shop Owner

Manufacturer Specific Definitions for P1125

Table of Contents

1. What Does Code P1125 Mean?
2. Where is the P1125 sensor located?
3. What are the common causes of code P1125?
4. What are the symptoms of code P1125?
5. Get Help with P1125

What Does Code P1125 Mean?

Special note on trouble codeP1125 and GM vehicles: While DTC P1125 is a manufacturer-specific code that may affect several OBD II compliant vehicles, the causes and symptoms of this code typically vary between most vehicle makes. This article will therefore deal with code P1125 as it applies specifically to GM vehicles.

OBD II fault code P1125 is a manufacturer-specific trouble code that is defined by carmaker GM as “Accelerator Pedal Position Sensor Fault”, or, sometimes as “Accelerator Pedal Position (APP) System”, and is set when the PCM (Powertrain Control Module) detects a miscorrelation between-

• two or more sensors in the throttle pedal position sensor assembly, or,
• a miscorrelation between two or more sensors in the throttle position sensor assembly and the electronic throttle actuator in the throttle body.

On many GM products, the throttle control mechanism is of the drive-by-wire type, which means that there is no physical connection such as a control cable between the throttle pedal and the throttle body.

In practice, and on a fully functional throttle control system, movement of the throttle pedal causes a reference voltage to change in direct response to the throttle pedal’s movement. The changing voltage is interpreted by the PCM as changes in the position of the throttle pedal, and depending on the resulting change in the reference voltage, the PCM will rotate the throttle plate to a position that corresponds to the position of the throttle pedal.

For example, if the throttle pedal is in the rest position, the throttle plate will be in the closed position. Conversely, if the throttle pedal is in the fully depressed position, the throttle plate will be in the WOT (Wide Open Throttle) position. In practice, the throttle body incorporates a stepper motor that is connected to the throttle plate, and in theory, the stepper motor’s rotation will be in direct proportion to the changes in the throttle pedal.

In the real world, however, the throttle pedal assembly contains up to three sensors, with only one sensor that is directly involved with controlling the position of the throttle plate. The other sensors serve to monitor a) the movement of the throttle pedal, and b), the correlation between the primary throttle pedal position sensor and the throttle plate. While this system works reasonably well on new vehicles, continuous use of the throttle pedal causes mechanical parts in the pedal assembly to wear out, and a harsh operating environment causes wear and tear on the throttle actuator’s motor and drive gears.

Thus, as a vehicle ages, the combined, and cumulative effects of excessive mechanical components of the throttle control system can cause miscorrelations between the positions of the throttle pedal and the throttle plate. While drive-by-wire throttle control systems have some capacity to compensate for mechanical wear of parts, this ability is limited, and easily overcome when several mechanical components wear out at different rates.

It should be noted though that while the definition of this code refers to throttle pedal position sensor faults, which suggests failures, defects, or malfunctions in one or more sensors, as opposed to miscorrelations between sensors, the fact is that failures, defects, or malfunctions in these sensors are primarily caused by excessive mechanical wear of sensor parts.

Therefore, while miscorrelations typically occur as the result of worn-out parts, OBD II systems cannot identify the actual parts that may be worn out, which explains why this code does not specifically refer to sensor miscorrelations, but to failures, defects, or malfunctions, that cause miscorrelations.

This is of course not the same as saying that mechanical wear is the only possible cause of code P1125 on all GM products, but is the primary cause of this code on older or high-mileage GM applications. For more information on other possible causes, see the Common Causes section.

Nonetheless, when the PCM detects any failure or malfunction in any sensor in the throttle pedal position sensor, it will recognize that it cannot control the throttle effectively, and it will set code P1125, and illuminate a warning light as a result. In some cases, and depending on the exact nature of the problem, the PCM may also initiate a “reduced Power” mode, which is GM-speak for a limp mode, which will persist until the fault is corrected.

Where is the P1125 sensor located?

This image shows the throttle pedal position sensor on a 2008 Chevy Malibu. In this example, the yellow arrow indicates the actual throttle pedal, the red arrow indicates the pedal position sensor, and the green arrow indicates the sensor’s electrical connector.

While the actual appearance of the throttle pedal position sensor on other GM applications differs from this example, the actual pedal position sensor will always be located on, or be attached to the throttle pedal. Thus, in some cases, it may be possible to replace only the actual sensor, while in other cases the throttle pedal must be replaced as a complete assembly.

What are the common causes of code P1125?

NOTE #1: Be aware that diagnosing this code on GM applications typically requires the use of GM-specific diagnostic equipment, although it might be possible to extract some additional fault codes with a high-end scan tool. Since there are several sensors involved in throttle control, a dealer-grade scan tool with bi-directional controls is required to perform the 18 steps that must be completed in the correct order to make a definitive diagnosis. Moreover, replacing a throttle pedal position sensor on a GM application often also requires that a prescribed “relearn” procedure be performed, which procedure is best performed with dealer-grade equipment.

NOTE #2: Given the difficulty of diagnosing this code on GM applications, the easiest option is often to just replace the pedal position sensor with an OEM part, or at least, an OEM-equivalent part. In nine out of every instances of this code, replacing the complete pedal assembly will resolve the issue definitively.

Typical causes of code P1125 on GM vehicles could include one or more of the following-

• Damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors
• Excessive mechanical wear of one or more throttle control components
• Defective or malfunctioning throttle pedal position sensor(s)
• Defective or malfunctioning throttle control actuator or throttle plate position sensor
• The loss or corruption of critical software, such as might happen when the battery is disconnected
• Failure to perform a prescribed relearn procedure correctly during a previous replacement or service/maintenance procedure
• The use of incorrect, unsuitable, or substandard aftermarket throttle pedal position sensor(s)
• Failed or failing PCM, but note that since this a rare event, the fault must be sought elsewhere before any control module is reprogrammed or replaced

What are the symptoms of code P1125?

Common symptoms of code P1125 could include one or more of the following-

• Stored trouble code and illuminated warning light
• In some cases, several additional codes could be present along with P1125
• The engine may not respond to throttle inputs, or responses may be severely limited
• Systems like cruise control, adaptive cruise control, traction control, and stability control might be unavailable or disabled since these systems depend on the throttle control system to be functional to operate
• The vehicle may be in Reduced Power mode, which typically limits engine power severely and locks automatic transmissions in one gear
• Depending on the nature of the problem and the application, the idling speed may be above or below a specified value, or the engine may not idle at all
• Depending on the nature of the problem, the PCM may also initiate and maintain a no-start condition as a safety precaution until the fault is corrected

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