P2135 – Throttle/Pedal Position Sensor/Switch A / B Voltage Correlation

dhakdev

3 months ago

What is Code P2135?

P2135 is a generic powertrain diagnostic trouble code that stands for "Throttle/Pedal Position Sensor/Switch A / B Voltage Correlation". This means the engine control module (ECM) has detected that the voltage signals from the throttle position (TP) sensor and/or accelerator pedal position (APP) sensor do not correlate with each other as expected.

In our workshop, we've seen the P2135 code pop up quite frequently across various makes and models. Just last week, a customer brought in their Audi A4 with this very issue. The car had reduced power and would intermittently enter limp mode. After diagnosing the problem, we found that the throttle position sensor was giving erratic readings, causing the ECM to detect a discrepancy with the accelerator pedal position sensor. We've had similar experiences with BMWs, Mercedes, and even the occasional Volvo. It seems that European cars are just as susceptible to this problem as their American and Asian counterparts. Regardless of the make, the culprit is usually a faulty throttle position sensor or wiring issue, which can be tricky to diagnose without the right tools and expertise.

Symptoms and Severity of P2135

When code P2135 is triggered, common symptoms include:

Reduced engine power (may enter "limp home" mode)
Difficulty accelerating or surging during acceleration
Engine stalling, especially after stopping
High idle RPMs
Check engine light illumination

Driving with P2135 present is not recommended, as the vehicle may stall unexpectedly. It's best to diagnose and repair the issue as soon as possible. While it may be okay to drive short distances to a repair shop, extended driving is inadvisable.

Throttle Control System Overview

Modern vehicles use an electronic throttle control (ETC) system to regulate engine power. The main components are:

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Accelerator pedal position sensors – Potentiometers that provide voltage signals indicating pedal position
Throttle position sensors – Potentiometers on the throttle body that indicate throttle plate angle
Throttle actuator control motor – Opens and closes the throttle plate based on driver input

The ECM monitors the TP and APP sensor signals to determine the driver's torque request. It expects the voltages to correlate with each other in a predictable manner. If the values do not match up, code P2135 will be stored.

Common Causes of P2135

Potential causes of this code include:

Faulty throttle position sensor (most common)
Damaged wiring or poor connections to sensors
Issues with throttle body
Faulty accelerator pedal position sensor
Malfunctioning ECM (rare)

Diagnosing P2135

To properly diagnose the root cause of P2135, follow these steps:

Scan for all codes. P2135 may appear with other throttle-related faults like P2122, P2123, P2127, P2128, etc.
Check the wiring and connections at the throttle body and accelerator pedal. Look for damaged wires, bent pins, or loose connections. Repair as needed.
With the key on, engine off, use a scan tool to view live data for the TP and APP sensors:
- TP sensor voltage should be 0.5-0.7 V at closed throttle and 4.0-4.5 V at wide open throttle
- APP sensor voltage should be 0.5-0.9 V with pedal released and 3.5-4.5 V at full throttle
If TP or APP voltages are out of range or erratic, test the sensors themselves per manufacturer specs. Replace a faulty sensor.
If sensors test okay, suspect a wiring issue, faulty throttle body, or rarely a bad ECM.

Repairing P2135

Once the cause is identified, perform the appropriate repair:

Replace a faulty TP or APP sensor
Repair damaged wiring
Clean the throttle body if dirty (may not fix underlying cause)
Replace the throttle body assembly
Reflash or replace the ECM if faulty

After repairs, clear codes and road test to verify the fix. On some vehicles, a throttle body relearn procedure is needed after replacement.

Preventing P2135

While this code can't always be avoided, a few steps can minimize risk:

Avoid aftermarket "performance chips" that alter throttle mapping
Only use a quality scan tool for diagnostics
Maintain the throttle body and sensors per the maintenance schedule
Address any drivability concerns promptly

P2135 Repair Cost

Depending on the root cause, repair costs for P2135 can range from $100-$1000:

TP or APP sensor replacement: $75-$200 ($50-$150 part + 0.5-1.0 labor hours)
Throttle body replacement: $250-$650 ($150-$500 part + 1.0-2.0 labor hours)
ECM replacement: $500-$1000 ($400-$800 part + 1.0-2.0 labor hours)

Actual costs will vary based on vehicle make and model, local labor rates, and parts pricing.

By understanding code P2135, its causes, and the diagnostic and repair process, vehicle owners and technicians can efficiently resolve this issue and restore proper throttle control system operation.

Frequently Asked Questions About P2135

What does OBD-II code P2135 mean?

Code P2135 stands for "Throttle/Pedal Position Sensor/Switch A / B Voltage Correlation". It indicates the engine control module (ECM) has detected the voltage signals from the throttle position (TP) sensor and accelerator pedal position (APP) sensor do not match each other as expected.

What are the symptoms of code P2135?

Common symptoms when P2135 is triggered include:

Reduced engine power, may enter "limp home" mode
Hesitation or surging during acceleration
Engine stalling after stopping
High idle RPMs
Check engine light illumination

Is it safe to drive with a P2135 code?

No, it's not recommended to drive with P2135 present as the vehicle may stall unexpectedly. While you may be able to drive short distances to a repair shop, extended driving is inadvisable. The issue should be diagnosed and repaired as soon as possible.

What causes code P2135?

Potential causes of P2135 include:

Faulty throttle position sensor
Damaged wiring or poor electrical connections
Issues with the throttle body
Faulty accelerator pedal position sensor
Rarely, a malfunctioning ECM

How do you diagnose the cause of P2135?

To diagnose P2135:

Scan for all codes, P2135 may appear with other throttle-related faults.
Check the wiring and connections at the throttle body and accelerator pedal.
Use a scan tool to view live data for the TP and APP sensors.
Test the TP and APP sensors per manufacturer specs.
If sensors are okay, suspect wiring, throttle body, or ECM issues.

What repairs can fix code P2135?

Repairs for P2135 may include:

Replacing a faulty TP or APP sensor
Repairing damaged wiring
Cleaning the throttle body
Replacing the throttle body assembly
Reflashing or replacing the ECM

Is there a difference between TP sensor 1 and 2?

Most drive-by-wire throttle bodies use two TP sensors for redundancy. TP sensor 1 is the main sensor while TP sensor 2 is for backup. The ECM compares the signals from both to ensure accuracy. A discrepancy between the two can trigger P2135.

What voltage readings are normal for the TP and APP sensors?

With the key on, engine off:

TP sensor voltage should be 0.5-0.7 V at closed throttle and 4.0-4.5 V at wide open throttle.
APP sensor voltage should be 0.5-0.9 V with pedal released and 3.5-4.5 V at full throttle.

Can a bad throttle body cause P2135?

Yes, a faulty throttle body can cause the TP sensors to send erratic or illogical signals, triggering code P2135. Cleaning the throttle body may provide a temporary fix but the underlying cause should still be addressed.

What does an electronic throttle actuator do?

The electronic throttle actuator is a motor that opens and closes the throttle plate based on driver input. It works in conjunction with the TP and APP sensors to regulate airflow into the engine. Issues with the actuator can lead to P2135.

Will disconnecting the battery clear code P2135?

Disconnecting the battery may temporarily clear the code from the ECM's memory. However, if the underlying problem is not fixed, the code will likely reappear once the fault is detected again.

Can a vacuum leak cause code P2135?

While a vacuum leak is more likely to trigger a lean condition code like P0171 or P0174, it's possible for a severe leak to affect the throttle control system. This could potentially contribute to code P2135 being set.

How much does it cost to fix code P2135?

The cost to repair P2135 varies based on the root cause:

TP or APP sensor replacement: $75-$200
Throttle body replacement: $250-$650
ECM replacement: $500-$1000
Actual costs depend on the vehicle, labor rates, and parts prices.

Is a throttle body relearn needed after replacing sensors?

On many vehicles, a throttle body relearn procedure must be performed after replacing the TP sensors, APP sensor, or throttle body itself. This allows the ECM to recalibrate the throttle control system. Consult service information for the specific relearn steps.

Can low battery voltage trigger P2135?

Low battery voltage can cause a variety of unusual sensor readings. While it's not a common cause of P2135, it's worth checking battery health and charging system output if the code persists after other repairs.

Are there any TSBs or recalls for P2135?

Some vehicle makes have released technical service bulletins (TSBs) related to P2135. These may outline known issues and specific repair procedures. Any applicable TSBs should be followed when diagnosing and repairing this code. Checking for recalls is also advised.

Can P2135 be caused by aftermarket parts?

Aftermarket sensors, throttle bodies, or "performance chips" can potentially trigger P2135 if they are not compatible with the factory ECM calibration. Using OEM or high-quality replacement parts is recommended to avoid such issues.

What other codes may appear with P2135?

Related codes that may appear alongside P2135 include:

P2122 – Throttle Position Sensor 'D' Circuit Low
P2123 – Throttle Position Sensor 'D' Circuit High
P2127 – Throttle Position Sensor 'E' Circuit Low
P2128 – Throttle Position Sensor 'E' Circuit High
P2138 – Throttle/Pedal Position Sensor/Switch 'D'/'F' Voltage Correlation

How often should the throttle body be cleaned?

For preventive maintenance, the throttle body should be cleaned every 75,000 miles (120,000 km) or as specified in the owner's manual. More frequent cleaning may be needed if the vehicle experiences driveability issues related to carbon buildup on the throttle plate.

What is the difference between pedal follower and pedal commander?

In a pedal follower system, the ECM controls the throttle plate position to match APP sensor input. The APP sensor "commands" the throttle.

In a pedal commander setup, the ECM opens the throttle based on other data like engine load and RPM, with the APP sensor providing more of a "suggestion". This allows for smoother operation and more consistent idle.

Consulting the service manual can confirm which type a particular vehicle uses. Regardless of setup, a correlation issue between the APP and TP sensors can trigger P2135.

Query: Please provide a comprehensive article on P2135 for my automotive blog targeted at engineers and mechanics. Include technical details on the throttle control system, common causes and symptoms, step-by-step diagnosis, and repair information. Use both metric and imperial units where applicable.