OBD-II Code P2135: Understanding Throttle/Pedal Position Sensor Voltage Correlation

OBD-II Trouble Code Technical Description: Throttle/Pedal Position Sensor/Switch A / B Voltage Correlation

Authored by a Certified Automotive Technician

The P2135 diagnostic trouble code is a common OBD-II powertrain code that is considered generic, meaning it can occur in most makes and models of vehicles manufactured from 1996 onwards. However, specific repair procedures may vary slightly depending on the vehicle’s year, make, and model.

The OBD-II code P2135, specifically “Throttle/Pedal Position Sensor/Switch A/B Voltage Correlation,” indicates a problem within your vehicle’s electronic throttle control system. This issue centers around the correlation of voltage signals between two throttle position sensors (TPS), impacting the throttle’s ability to operate correctly.

Decoding the Electronic Throttle Control System

Since the 1990s, the automotive industry has widely adopted “drive-by-wire” throttle control technology. This advancement replaces the traditional mechanical cable connecting the accelerator pedal to the throttle body with an electronic system. The drive-by-wire system enhances control over crucial vehicle functions, including emissions, fuel economy, traction control, stability control, cruise control, and transmission responses.

In older, cable-operated systems, the throttle was directly linked to the gas pedal. A Throttle Position Sensor (TPS) mounted on the throttle body would then convert the throttle plate’s position into a voltage signal for the engine control module (ECM) to manage engine performance.

Modern electronic throttle control systems are more complex, comprising:

• Accelerator Pedal Position Sensor (APPS): This sensor measures the driver’s input from the accelerator pedal.
• Electronic Throttle Body: This unit includes an electric motor to control the throttle plate opening.
• Dual Throttle Position Sensors (TPS): Integrated within the throttle body, these sensors provide redundant feedback on the throttle plate’s position.
• Engine Control Module (ECM): The computer that manages the entire system, interpreting sensor data and controlling the throttle motor.

While the core meaning of the P2135 code remains consistent, different manufacturers might use slightly varied descriptions. For example, you might see “Throttle position sensor circuit range/performance” on an Infiniti or “Electronic throttle control system malfunction power management” on a Hyundai.

When you press the accelerator pedal, the APPS signals the ECM about the desired throttle opening. The ECM then commands the throttle body’s electric motor to adjust the throttle plate accordingly. The two embedded TPS sensors then report the degree of throttle opening back to the ECM as voltage signals.

The ECM constantly monitors and compares the voltage signals from both TPS sensors. When these signals correlate and agree within a specified range, the system operates as intended. However, if the ECM detects a discrepancy or a lack of correlation between these voltage signals for a duration of two seconds or more, it triggers the P2135 code, indicating a system malfunction. This situation can be potentially dangerous as it can lead to unpredictable throttle behavior and loss of control. It’s important to note that other diagnostic trouble codes might accompany P2135, providing further insight into the specific nature of the problem.

Image of an accelerator pedal with integrated sensor and wiring harness. Photo courtesy of Panoha (Own work) under GFDL, CC-BY-SA-3.0, or FAL licenses, via Wikimedia Commons.

Important Note: The P2135 DTC shares its diagnostic procedures with similar codes such as P2136, P2137, P2138, P2139, and P2140, as they all relate to throttle position sensor issues.

Symptoms of a P2135 Code

Experiencing a P2135 code can manifest in various symptoms that affect your vehicle’s driveability. These symptoms can range in severity and may include:

• Stalling: The engine may stall, particularly when decelerating or coming to a stop.
• Lack of Power: Reduced engine power and sluggish acceleration.
• No Acceleration: The vehicle may fail to accelerate even when the accelerator pedal is pressed.
• Sudden Power Loss: Unexpected loss of power while driving at cruising speeds.
• Stuck Throttle: The throttle may become stuck at a certain RPM, leading to unintended acceleration or difficulty decelerating.
• Check Engine Light: Illumination of the malfunction indicator lamp (MIL), commonly known as the check engine light.
• Code Set: The P2135 trouble code will be stored in the ECM’s memory and can be retrieved with an OBD-II scanner.

Potential Causes of the P2135 DTC

Several factors can contribute to a P2135 code. Based on field experience, common causes include:

• Faulty Throttle Body Connector/Wiring: Poor electrical connections at the throttle body connector are a frequent culprit. This can involve corroded terminals, loose connections, or wires pulling out of the connector (“pigtail”).
• Wiring Issues: Bare wires in the throttle body pigtail may short circuit to ground, disrupting the sensor signals.
• Distorted Throttle Body Cover: Damage or distortion to the top cover of the throttle body can interfere with the internal gears that control the throttle plate movement.
• Defective Electronic Throttle Body: The throttle body assembly itself, including the TPS sensors or the motor, may be faulty.
• Failed Accelerator Pedal Sensor (APPS): Malfunction of the accelerator pedal position sensor or its associated wiring.
• Engine Control Module (ECM) Failure: In rare cases, a failing ECM can cause incorrect signals or misinterpret sensor data.
• TPS Sensor Miscorrelation/Relearn Needed: Minor discrepancies in TPS sensor readings might occur, requiring the ECM to undergo a relearn procedure to re-establish proper throttle control. In some cases, the ECM may need reprogramming by a dealer.

Diagnostic and Repair Steps for P2135

Working with electronic throttle control systems requires caution, as they are sensitive to damage. Handle components with care to prevent further issues.

1. Technical Service Bulletins (TSBs): Begin by checking for TSBs related to P2135 and your specific vehicle. TSBs are manufacturer-issued recommendations for known problems and repair procedures. You can usually find TSB information online or through a vehicle service manual database.

2. ECM Relearn Procedure: Consult your vehicle’s service manual or online resources for a potential ECM relearn procedure. This process can sometimes resolve minor sensor miscorrelation issues. An example for Nissan vehicles involves specific ignition and pedal manipulation steps to reset the system.

3. Address Accompanying Codes: If other DTCs, such as P2136 or related codes, are present, address them first. These codes might pinpoint a more specific component failure that is also causing the P2135 code.

4. Inspect Throttle Body Connector: Carefully disconnect the electrical connector at the throttle body. Examine the connector and terminals for:

   • Bent or Missing Terminals: Check for any damage to the pins or sockets.
   • Corrosion: Look for signs of green or white corrosion on the metal terminals.
   • Loose Terminals: Ensure the terminals are firmly seated in the connector housing.
   • Wire Damage: Inspect the wires near the connector for any signs of damage, fraying, or breaks.
     Clean any corrosion with a small tool or electrical contact cleaner. Apply dielectric grease to the terminals before reconnecting to improve connection and prevent future corrosion. If the connector is damaged, consider replacing the pigtail connector, available from auto parts stores or dealerships.

5. Check Throttle Body Cover: Inspect the plastic top cover of the throttle body for any cracks, warping, or distortion. If damage is present, consult a dealer to see if the cover is available separately; otherwise, throttle body replacement might be necessary.

6. Test Accelerator Pedal Sensor (APPS): Use a voltmeter to test the APPS. Identify the 5-volt reference wire and the signal wire (refer to wiring diagrams for your vehicle). With the ignition on, slowly depress the accelerator pedal. The signal voltage should increase smoothly from approximately 0.5 volts to 5.0 volts as the pedal is depressed. Replace the APPS if the voltage signal is erratic, exhibits spikes, or is absent.

7. Check Throttle Body Motor Power: Identify the power and ground terminals for the throttle body motor (refer to wiring diagrams). With a helper turning the ignition to the “on” position and slightly depressing the accelerator pedal, probe for voltage at the motor connector. If power is absent, suspect an ECM issue or wiring problem. If power is present, the throttle body assembly is likely faulty and requires replacement.

Further Reading: For additional information, research articles like “UnderhoodService GM reduced engine power article” for insights into related issues in specific vehicle makes.

Other Throttle Related DTCs: Explore information on related diagnostic trouble codes like P0068, P0120, P0121, P0122, P0123, P0124, P0510, and others to broaden your understanding of throttle control system problems.

Related DTC Discussions

For further assistance and community support, consider joining online automotive forums where you can discuss your specific P2135 code issue with other vehicle owners and technicians.

Need More Help with a P2135 Code?

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Disclaimer: This information is for informational purposes only and should not be considered as professional repair advice. We are not liable for any actions taken based on this information. Always consult with a qualified automotive technician for diagnosis and repairs. All content is copyright protected.