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

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The P2135 OBD2 code triggers when the sensors in the electronic throttle control system aren’t correlating properly. When the system is functioning correctly, the throttle positions sensors and accelerator pedal sensor will all ready within about .5 volts of each other. Readings outside this range indicate a fault somewhere in the system.

The electronic throttle system is one of the most delicate components in a modern engine. It must be handled very carefully to avoid further damage. For that reason, inexperienced DIY-ers will likely want to consult a mechanic before replacing any components. 

The sensors in the electronic throttle control system are triggered by the P2135 code when these aren't correlating properly
The P2135 OBD2 code triggers when the sensors in the electronic throttle control system aren’t correlating properly

P2135 Code Definition: Throttle/Pedal Pos Sensor/Switch A/B Voltage Correlation 

What Does P2135 Mean?

The P2135 OBD2 code indicates the throttle is having difficulty opening and closing properly. While this is a generic powertrain code applicable to any OBD2-equipped vehicle, the repair steps will differ depending on the design of your throttle.

Most vehicles on the road today use electronic throttle control. This allows more control of the fuel economy and transmission response than simpler manual throttle control. It’s also what makes conveniences like cruise control possible.

Electronic throttle control systems use sensors on the accelerator pedal and throttle position to ensure the throttle is opening the correct amount. When you press the accelerator, the attached sensor tells the engine computer how much you want to open the throttle, and communicates this to the motor, opening the throttle plate. 

On the other end, two sensors in the throttle body read how much the throttle plate opens, sending this data back to the engine computer. If the voltage of the signal sent to the throttle doesn’t match the reading from the throttle position sensors, the P2135 trouble code is activated. 

Issues with the throttle position can lead to dangerous driving conditions. Because of this, activation of the P2135 trouble code may cause your vehicle to enter “limp home mode”. When this happens, you’ll be unable to drive over 20 miles an hour until the code has been cleared. 

You will often see other trouble codes alongside P2135. Diagnostic codes P2135-P2140 are essentially the same, and you’ll follow the same diagnostic steps for all of them. These codes can be useful in directing you to the specific component causing the trouble code. 

What Are The Symptoms Of The P2135 Code?

  • Activation of the check engine light
  • Stalls, especially while idling
  • Reduced engine power
  • Sudden power loss when cruising
  • Inability to accelerate
  • Surges or hesitation when accelerating
  • Engine revs when the gas pedal wasn’t pressed
  • Surging or elevated revolutions per minute (RPMs)

What Are The Causes Of P2135?

  • Malfunctioning throttle position sensor(s)
  • The malfunctioning accelerator position sensor
  • Open, short, or damaged wires around the throttle position sensor(s) or accelerator position sensor
  • Corrosion on wiring connector of the throttle body
  • Damage or distortion to throttle body cover
  • PCM or ECM requires programming update
  • Faulty PCM or ECM

How Serious Is The P2135 Code?

The P2135 trouble code is very serious. Your engine could stall or lose power, and that can be dangerous if it happens while you’re driving. Even if your vehicle doesn’t enter a failsafe mode, you should stop driving your vehicle until you’ve repaired the problem. 

How To Diagnose And Fix The P2135 Code

Tools you’ll need:

  1. Check for any technical service bulletins related to P2135 for your vehicle. In some cases, this code triggers when the engine software requires an update. If this is the case, you’ll see it in your vehicle’s technical service bulletin history. 
  2. Read all codes using an OBD2 scanner. Make note of any trouble codes that appear alongside P2135, as these could help guide your diagnosis. 
  3. Remove the electrical connector from the throttle body. Examine the connector for corrosion and damage, such as missing or bent pins. Light corrosion can be cleaned away. If the connector is damaged, replace it. 
  4. Visually inspect the top cover of the throttle body. In some cases, this cover can distort and prevent the movement of the gears. Replace the cover if you see any cracks or warping. Some vehicles don’t offer replacement covers, in which case you’ll need to replace the entire throttle body.
  5. Inspect the wires around the accelerator pedal sensor, throttle position sensors, and wiring harness. Replace any frayed or damaged wires, and make sure all the wires are properly connected. Clean away any corrosion you see on connector plates. 
  6. Check the accelerator pedal sensor using a multimeter. You should read a 5-volt reference signal, as well as a variable signal that slowly climbs from .5 volts to 5 volts as you depress the accelerator pedal. If the voltage spikes or you read no voltage, replace the sensor. 
  7. Use a multimeter to probe the throttle body connector. Have an assistant turn on your engine and slightly depress the accelerator while you probe the wire. If it’s receiving power, the problem is further on within the throttle body. Test the throttle position sensors with a multimeter and replace them if the readings don’t match the specifications in your manual. 
  8. If there is no power, the problem is either with the wiring or the engine computer. Use a multimeter to test the wires for open and short circuits. If no problems are detected, take your vehicle to a mechanic for further diagnosis of the ECM or PCM. 

Common Mistakes To Avoid While Diagnosing The P2135 Code

Keep careful track of which sensors you’re testing as you go through the diagnosis. Even experienced mechanics can confuse the two throttle position sensors, leading to the replacement of the wrong one.

Also, keep in mind that the electronic throttle system is very sensitive. Take care not to jostle or drop any components during your diagnosis or you could end up needing to replace the entire system. 

Tips To Avoid P2135 In The Future

Missing updates to your engine computer don’t always cause problems right away. It’s a good idea to check periodically for technical service bulletins related to your vehicle even if it seems to be running smoothly. This will let you stay on top of required updates and other service information before it becomes a problem. 

Read more: P0121 Code: Meaning, Symptoms, Causes, Diagnostics, and Fixes