OBD-II Code P2135: Throttle/Pedal Position Sensor/Switch A/B Voltage Correlation Explained

In the realm of automotive diagnostics, the OBD-II trouble code P2135, often termed “Throttle/Pedal Position Sensor/Switch A / B Voltage Correlation,” signals a discrepancy within your vehicle’s electronic throttle control system. As a seasoned auto repair expert at autelfrance.com, I’m here to break down this code, helping you understand its implications, symptoms, potential causes, and diagnostic steps.

Decoding the P2135 Diagnostic Trouble Code

The P2135 code is classified as a generic powertrain code, meaning it’s relevant across a wide spectrum of vehicle makes and models manufactured from 1996 onwards. While the fundamental meaning remains consistent, specific repair procedures can vary slightly depending on your vehicle’s make and model.

At its core, code P2135 indicates an issue with the correlation of voltage signals between two throttle position sensors (TPS) within your vehicle’s electronic throttle control system. This system, a standard in modern vehicles since the 1990s, replaced the traditional cable-operated throttle with an electronic system to enhance control over emissions, fuel efficiency, traction, stability, cruise control, and transmission performance.

From Throttle Cables to Drive-by-Wire: A Technological Leap

Historically, throttle control was mechanical. A cable directly linked the gas pedal to the throttle plate, modulating engine speed. A Throttle Position Sensor (TPS) was introduced to convert throttle movement into an electrical signal for the engine computer.

Modern vehicles employ “drive-by-wire” or Electronic Throttle Control (ETC). This sophisticated system comprises:

Accelerator Pedal Position Sensor (APPS): Monitors the driver’s requested acceleration.
Electronic Throttle Body: Houses an electric motor and dual embedded Throttle Position Sensors (TPS).
Engine Management Computer (PCM/ECM): The brain of the system, processing signals and controlling the throttle.

When you press the accelerator, the APPS sends a signal to the computer indicating your desired throttle opening. The computer then commands the throttle body’s electric motor to adjust the throttle plate. Crucially, two TPS sensors within the throttle body provide redundant feedback to the computer, confirming the throttle plate’s position.

Image of a throttle body, highlighting the TPS sensor:

Alt text: Throttle body with throttle position sensor (TPS) unit visible on the lower right side, showcasing the component responsible for monitoring throttle plate angle.

The engine computer constantly monitors the voltage signals from both TPS sensors. When these signals correlate and agree, the system operates correctly. However, if the voltage readings deviate from each other for a duration of two seconds or more, the P2135 code is triggered, indicating a malfunction within the ETC system. This discrepancy can lead to serious drivability issues and even safety concerns due to potential loss of throttle control.

It’s worth noting that while the P2135 code is generally consistent, some manufacturers may use slightly different terminology. For instance, Infiniti might describe it as “Throttle position sensor circuit range/performance,” while Hyundai could label it “Electronic throttle control system malfunction power management.” Regardless of the specific wording, the underlying issue and diagnostic approach remain largely the same.

Furthermore, the P2135 code is closely related to other DTCs like P2136, P2137, P2138, P2139, and P2140. These codes often point to similar issues within the TPS or ETC system, and the diagnostic steps are generally applicable across these related codes.

Symptoms Associated with OBD-II Code P2135

The symptoms of a P2135 code can vary in severity, ranging from subtle drivability issues to potentially dangerous situations. Common symptoms include:

Engine Stalling: Particularly when decelerating or coming to a stop.
Lack of Power: The engine may feel sluggish or unresponsive to accelerator input.
No Acceleration: The vehicle may fail to accelerate even when the gas pedal is pressed.
Sudden Power Loss: Unexpected loss of engine power, especially at cruising speeds.
Stuck Throttle: The engine RPMs may remain elevated even after releasing the accelerator pedal.
Check Engine Light: The malfunction indicator lamp (MIL) will illuminate on the dashboard.

These symptoms highlight the critical role of the throttle position sensors in engine management. When the signals become inconsistent, the engine computer struggles to accurately control the throttle, leading to these noticeable drivability problems.

Potential Causes of a P2135 Code

Several factors can contribute to a P2135 trouble code. Based on my experience in automotive repair, common causes include:

Faulty Throttle Body Connector/Wiring: A frequent culprit is a poor electrical connection at the throttle body connector, often referred to as the “pigtail.” Terminals within the connector can corrode, become loose, or even pull out, disrupting the signal flow.
Bare Wire Shorting to Ground: Damaged wiring in the throttle body pigtail can expose bare wires that may short circuit to ground, causing signal irregularities.
Distorted Throttle Body Cover: The plastic top cover of the throttle body, which houses the throttle plate gears, can become warped or distorted. This distortion can impede the smooth operation of the gears and affect TPS readings.
Defective Electronic Throttle Body: The throttle body itself, including the internal motor and TPS sensors, can fail. This could be due to component wear, electrical issues within the unit, or mechanical failure of the throttle plate mechanism.
Failed Accelerator Pedal Sensor: Although less common than throttle body issues, the accelerator pedal sensor or its associated wiring can malfunction, sending incorrect signals to the computer.
Engine Management Computer (PCM/ECM) Failure: In rare cases, a fault within the engine management computer itself can lead to a P2135 code. However, this is usually diagnosed after ruling out other potential causes.
TPS Relearn Procedure Required: Sometimes, the TPS sensors might lose their calibration or correlation. Performing a throttle relearn procedure can recalibrate the system and resolve the code. In some cases, the computer may require reprogramming at a dealership.

Image of an accelerator pedal with sensor and wiring:

Alt text: Accelerator pedal assembly showcasing the integrated position sensor and wiring harness, components crucial for transmitting driver input to the electronic throttle control system.
Photo used with permission by Panoha (Own work) GFDL, CC-BY-SA-3.0 or FAL, via Wikimedia Commons

Diagnosing and Repairing OBD-II Code P2135

Diagnosing and repairing a P2135 code requires a systematic approach. Remember that the electronic throttle control system is sensitive, so handle components with care. Avoid dropping orRough handling, as this can cause damage.

Here’s a step-by-step diagnostic and repair process:

Check for Technical Service Bulletins (TSBs): Begin by searching online for TSBs related to P2135 for your specific vehicle make and model. TSBs are issued by manufacturers to address known issues and provide recommended repair procedures. They can offer valuable insights and shortcuts in the diagnostic process.
Perform a Throttle Relearn Procedure: Consult your vehicle’s service manual or online resources for a potential throttle relearn procedure. This procedure can sometimes reset the computer and resolve minor TPS correlation issues. An example for Nissan vehicles is provided in the original article, but procedures vary by manufacturer.
Address Additional DTCs First: If other trouble codes are present alongside P2135, especially codes related to the TPS or ETC system (like P2136), prioritize diagnosing and resolving those codes first. These related codes might be the root cause of the P2135.
Inspect the Throttle Body Connector: Carefully disconnect the electrical connector from the throttle body. Thoroughly inspect the connector terminals for:
- Corrosion: Look for any signs of green or white deposits on the metal terminals. Clean corrosion using a small screwdriver or electrical contact cleaner.
- Bent or Missing Terminals: Check for bent or broken pins within the connector.
- Loose Terminals: Ensure the female terminals are securely seated in the connector housing and haven’t been pushed out.
Apply a small amount of dielectric grease to the terminals to prevent future corrosion and improve electrical contact before reconnecting the connector.
Replace the Throttle Body Pigtail (If Necessary): If you find bent, missing, or severely corroded terminals in the throttle body connector, consider replacing the pigtail. New pigtails are typically available at auto parts stores or dealerships.
Inspect the Throttle Body Cover: Examine the top plastic cover of the throttle body for any signs of cracks, warping, or distortion. If damage is evident, inquire at the dealership about purchasing a replacement cover. If a separate cover isn’t available, throttle body replacement may be necessary.
Test the Accelerator Pedal Sensor: Use a voltmeter to test the accelerator pedal sensor. You should typically find a 5-volt reference voltage and a signal wire. With the ignition key turned to the “ON” position, slowly depress the accelerator pedal. The voltage on the signal wire should smoothly increase from approximately 0.5 volts to 5.0 volts without spikes or dropouts. Replace the accelerator pedal sensor if the voltage readings are erratic or absent.
Check for Power at the Throttle Body Motor: Identify the power and ground terminals for the throttle body motor (refer to wiring diagrams for your specific vehicle). Use a voltmeter to check for voltage at the motor connector when a helper turns the ignition on and slightly depresses the accelerator pedal.
- No Power: If no power is present at the motor, suspect a fault with the engine management computer or the wiring harness between the computer and throttle body.
- Power Present: If power is reaching the motor, the throttle body itself is likely faulty and requires replacement.

For more in-depth information, you can refer to resources like this article on GM reduced engine power issues: UnderhoodService GM reduced engine power article.

Related OBD-II Codes: Explore these related throttle-related DTCs for a broader understanding of potential issues: P0068, P0120, P0121, P0122, P0123, P0124, P0510, and others.

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