Vehicles with electronic throttle control use two throttle position signals, called A and B, so the engine computer can cross-check where the throttle plate really is. A P2135 code means the engine computer found a problem with the throttle position sensors.
Below you will find what the code means, the common causes, step-by-step tests and typical repair costs.
P2135 Code Breakdown
Every OBD-II code follows the same five-character pattern set by the SAE J2012 standard. Each character narrows down which system has the fault. This table shows what each part of the code tells you.
| Character | Meaning | What It Tells You |
|---|---|---|
| P | Powertrain | The fault is in the engine or transmission systems. |
| 2 | Generic (SAE) code | The definition is the same on every OBD-II vehicle. |
| 1 | Fuel and air metering | The fault involves fuel and air metering, such as airflow, temperature, throttle and oxygen sensors or fuel control. |
| 35 | Specific fault | Throttle/Pedal Position Sensor/Switch “A”/”B” Voltage Correlation |
What the P2135 Code Means
The SAE J2012 standard defines the P2135 code as Throttle/Pedal Position Sensor/Switch “A”/”B” Voltage Correlation. The two signals come from sensors in the throttle body. They move in a fixed relationship to each other, for example one rising while the other falls. The computer compares them all the time. If they disagree by more than a small amount, it cannot trust either, so it sets this code and usually limits throttle opening.
On some vehicles, this code can also point to the two accelerator pedal position signals. Dirty throttle bodies, worn sensor tracks, a loose connector and a shared reference voltage fault are common causes.
The throttle sensors share a 5-volt reference and ground with each other and sometimes with other sensors. A fault on that shared circuit can make both signals shift together in odd ways, which also sets this code.
A correlation code means two signals that should agree do not. The PCM compares them all the time, and when the difference stays too large for too long, it sets this code and may limit power to protect the engine.
Symptoms of a Throttle Sensor Correlation Problem
Symptoms depend on the cause. Common signs of a P2135 code include:
- Check engine light on
- Reduced power or limp mode
- Poor throttle response
- Engine stuck at a fast idle
- Stalling
Most Common Causes of the P2135 Code
Correlation faults usually come from one of these:
- One sensor track worn or drifting. Most pedal and throttle sensors have two or three tracks in one housing.
- High resistance on one signal or ground. Corrosion shifts one reading but not the other.
- Shared reference voltage problem. A weak supply can pull one signal off.
- Damaged wiring. A rubbed wire can affect one circuit only.
- Wrong or aftermarket part. A sensor with the wrong output curve.
Tools You Will Need
You can do most of this testing at home with basic tools:
- OBD-II scan tool with live data and graphing
- Digital multimeter with back-probe pins
- Test light
- Wiring diagram for your vehicle
- Service manual or repair information
How to Diagnose the P2135 Code
Start with the quick checks, then test the parts and wiring before you buy anything.
Check Live Data and Freeze Frame
With the key on and the engine off, watch both throttle position signals in live data while you press the pedal slowly. Both should change smoothly and stay in step. A jump or flat spot on one points to the bad track.
Compare Both Signals in Live Data
With the key on and engine off, watch both signals in live data while you move the part slowly through its full range. Both should change smoothly and stay in step. A jump, flat spot or gap on one track shows the problem.
Check Reference and Ground
Back-probe each sensor track at the connector. The reference should be close to 5 volts and the ground close to 0 volts. A difference between tracks points to wiring rather than the sensor.
Clean and Inspect the Throttle Body
With the key off, look at the throttle plate and clean carbon from the bore. Do not force the plate open. Check the throttle body connector for corrosion and bent pins, and check the 5-volt reference and ground.
Wiggle Test the Connector
With the key on, watch both throttle signals in live data while you gently wiggle the throttle body connector and its wiring. A sudden jump on one signal points to a loose terminal or broken wire.
How to Fix the P2135 Code
Match the repair to what your tests found. Then clear the code and drive under the same conditions that set it.
- Clean the throttle body and run a relearn if needed.
- Repair the connector or wiring
- Replace the throttle body if a sensor track is worn.
- Replace the pedal position sensor if the pedal signals disagree.
Common Mistakes to Avoid
These mistakes waste money or leave the real fault in place:
- Replacing the sensor without checking each signal in live data
- Ignoring corrosion at the connector
- Replacing parts before testing them
- Ignoring other stored codes that point to the cause
Repair Cost Breakdown
Repair costs depend on the cause. This table shows typical ranges for parts and labor.
| Repair | DIY Cost | Typical Shop Cost |
|---|---|---|
| Throttle body cleaning | $5 to $15 | $75 to $150 |
| Connector or wiring repair | $10 to $50 | $100 to $300 |
| Throttle body | $150 to $500 | $300 to $800 |
| Pedal position sensor | $60 to $200 | $150 to $400 |
Is It Safe to Drive with a P2135 Code?
Drive with care. A P2135 code often puts the engine in limp mode with very little power, which can make merging dangerous. Have it fixed soon.
Related Codes
These codes often show up with this one or point to the same system:
| Code | Meaning |
|---|---|
| P0641 | Sensor Reference Voltage A Circuit Open |
| P0220 | Throttle Position Sensor B Circuit Malfunction |
| P0120 | Throttle Position Sensor A Circuit Malfunction |
Getting the Throttle Signals Back in Step
A P2135 code means the two throttle position signals disagree. Dirty or worn throttle bodies, loose connectors and reference voltage faults cause most cases.
- Compare both signals in live data.
- Check the connector and reference.
- Replace the throttle body only after testing.
Frequently Asked Questions
Why Does a Correlation Code Cut Power?
When two signals disagree, the PCM cannot tell which one is right. To stay safe, it may limit throttle opening or engine power until the fault clears. That is why a correlation code often comes with reduced power mode.
Does This Code Mean I Need a New Throttle Body?
Often, but not always. Check the connector, the wiring and the 5-volt reference first. A poor connection can make the two signals disagree. If they still disagree with good wiring, the sensors in the throttle body are worn.
Is This Code the Same on Every Vehicle?
Yes. It is a generic SAE code, so the definition is the same on every OBD-II vehicle. The parts that cause it and the test steps vary by make and engine, so check the service manual for your vehicle before you buy parts.
Can I Clean the Throttle Body Myself?
Yes. With the key off, remove the intake duct and wipe carbon from the plate and bore with throttle body cleaner on a cloth. Do not spray into the electric motor or force the plate open. Some vehicles need an idle relearn afterward.
Can a Bad Battery Cause This Code?
Low or unstable voltage can upset the throttle body motor and sensors. If you also see other electrical codes or the battery is weak, test the battery and charging system before replacing the throttle body.
Do I Need a Dealer to Fix This Code?
Not always. Most of the checks in this guide need only a scan tool, a multimeter and basic hand tools. A dealer or a well-equipped shop helps when the repair needs module programming, factory software or special tools.
Should I Check for Technical Service Bulletins?
Yes. Carmakers publish service bulletins for known problems, and some cover this code with updated parts or engine computer software. A dealer or a repair information service can check bulletins for your VIN before you spend money on parts.
Will This Code Clear Itself After the Repair?
If the fault is fixed, the check engine light usually turns off after about three drive cycles in a row with no fault. The stored code stays in memory for a while longer and then erases itself. You can clear it right away with a scan tool, but that also resets the readiness monitors, so the car will need some driving before an emissions test.