Stop Guessing: How to Fix the GM P2135 Code on Your Silverado

Overview

Let’s talk about a frustrating issue that plagues many GM Silverado owners: the P2135 code. This diagnostic trouble code (DTC) indicates a correlation error between your throttle pedal position sensor and the throttle body position sensor. In plain terms, the engine control module (ECM) has detected that the throttle body isn’t responding the way the pedal is telling it to. This typically leaves you in a reduced power or “limp home” mode, often with the check engine light and a “Service Stabilitrak” message on your dash.

For a Silverado, this is almost always a General Engine problem, tied directly to the electronic throttle control (ETC) system. The common culprits are a failing throttle body, a damaged wiring harness, or a faulty accelerator pedal position sensor. However, before you throw parts at it, there is a specific pattern to check.

My experience shows that the most frequent root cause on 2014-2019 Silverado 1500 models (and similar GMT K2XX trucks) is a failing throttle body. The internal throttle position sensors degrade over time, especially if the truck has seen high mileage or dirty air filters. The GM part number for a replacement throttle body is 12679524 (for 5.3L and 6.2L engines). Expect a labor time of about 1.0 to 1.5 hours for replacement and reprogramming.

Before you buy a new throttle body, perform a critical check. With the key on, engine off, listen for a faint “click” from the throttle body. If you hear a rapid clicking or no click at all, the internal motor or sensor is toast. Also, inspect the wiring harness connector at the throttle body for bent pins or corrosion. A poor connection can mimic a sensor failure.

If you replace the throttle body, you must perform a throttle body relearn procedure. You can often do this with a bidirectional scan tool, or you can try the manual method: turn the key to the “On” position (do not start), wait 60 seconds, then turn it off. Wait 10 seconds, then start the engine. This is not always successful, so a professional scan tool is recommended. A new throttle body from a dealer will cost roughly $250 to $350, plus about $120 to $150 for labor and programming.

Symptoms

The P2135 code in a Silverado indicates a correlation problem between the Throttle Position Sensor (TPS) 1 and TPS 2 signals inside the electronic throttle body. While this can be a sensor failure, the “woes” often point to deeper wiring or connector issues. Here are the specific warning signs and the most likely solution.

Warning Signs of P2135 in a Silverado

• Reduced Engine Power (Limp Mode): The most common symptom. The dash will display “Reduced Engine Power” and acceleration will be severely limited. You will be stuck at 20-30 mph.
• Stuttering or Harsh Shifting: The transmission will shift erratically because it receives conflicting data from the throttle body. This feels like a hard slam between gears.
• Unpredictable Idle: The engine may idle high (around 1200 RPM) or surge up and down. In some cases, the engine may stall when coming to a stop.
• Throttle Pedal Resistance: The accelerator pedal may feel stiff or unresponsive. Sometimes you can push the pedal to the floor with no engine response.
• Check Engine Light and Traction Control Light: Both will illuminate simultaneously. This is a clear indicator the PCM has lost confidence in the throttle position data.

Possible Solution (Wiring Repair)

Do not buy a new throttle body first. The most common root cause on 2014-2019 Silverado 1500s (and some 2500s) is a chafed wiring harness. The harness rubs against the engine cover or a bracket near the throttle body connector.

• Inspect the Harness: Look at the 6-pin connector on the throttle body. The wires (especially the orange and black wires for TPS signal) often break internally inside the insulation.
• Repair Method: Cut back the harness 2-3 inches from the connector. Solder in new pigtail wires and use heat-shrink tubing. Do not use crimp connectors—they fail again.
• Cost: A DIY repair costs about $15 for wire and heat-shrink. A shop will charge 1.5 to 2.0 labor hours ($150 to $250).
• GM Part Number: If the connector itself is damaged, use GM Pigtail Connector Part # 19354027 (about $45 at a dealer).
• Throttle Body Replacement: Only replace the throttle body if the wiring is perfect and the code returns. A genuine ACDelco throttle body (GM Part # 12681654) costs $250-$350 and takes about 1.0 hour to install.

Always start with the wiring inspection. The “Silverado P2135 Woes” are almost always a wire chafing issue, not a failed throttle body.

Diagnosis

How To Diagnose Silverado P2135 (Throttle/Pedal Position Sensor Correlation)

The P2135 code on a GM Silverado (typically 2007-2013 models with the 4.8L, 5.3L, or 6.2L engines) indicates a correlation error between the accelerator pedal position sensor (APP) and the throttle position sensor (TPS). This is a common issue that often leads to reduced engine power, limp mode, or a stuck throttle. Follow this step-by-step diagnostic process to pinpoint the root cause before replacing parts.

1. Verify the Code and Check for Related Codes
   Use a quality scan tool (Snap-on, Autel, or GM Tech 2) to read all stored codes. P2135 is often accompanied by P0121, P0122, P0123, P0221, P0222, or P0223. Write down all codes and freeze frame data. Clear the codes and test drive the truck. If P2135 returns immediately, proceed. A single occurrence may be a glitch.
2. Inspect the Throttle Body and Wiring Harness
   On Silverado V8 engines, the throttle body is located on the front of the intake manifold. Look for obvious damage: loose connectors, chafed wires near the throttle body or under the air intake tube, or corrosion at the 6-pin connector (GM part #12575154 for the pigtail). Check for oil contamination from the PCV system inside the throttle body bore—this can cause sticky throttle plates. Clean the throttle body with GM Throttle Body Cleaner (part #12378514) only. Never use brake cleaner or carb cleaner; it damages the TPS coating.
3. Test Throttle Position Sensor Voltage
   With the key ON, engine OFF, probe the throttle body connector at pin 3 (5V reference), pin 4 (TPS 1 signal), and pin 5 (TPS 2 signal). TPS 1 should read 0.5-1.0V at closed throttle and 4.0-4.5V at wide open throttle (WOT). TPS 2 should read 4.0-4.5V at closed throttle and 0.5-1.0V at WOT. The two signals must be opposite and sum to approximately 5V. If the voltage is erratic, missing, or stuck, replace the throttle body assembly (GM part #12679525 for most 5.3L/6.2L engines; labor 1.0-1.5 hours, typically $75-$150 for the part).
4. Test Accelerator Pedal Position Sensor Voltage
   The APP sensor is on the accelerator pedal assembly. With the key ON, engine OFF, probe the 6-pin connector at pins A (5V reference), B (APP 1 signal), C (low reference), D (5V reference), E (APP 2 signal), and F (low reference). APP 1 should read 0.4-0.8V at rest and 4.0-4.5V at full pedal. APP 2 should read 0.2-0.4V at rest and 2.0-2.5V at full pedal. If either signal is out of range or erratic, replace the pedal assembly (GM part #25960422; labor 0.5 hours, part about $80-$120).
5. Check the 5V Reference Circuit for Shorts
   A short in the 5V reference circuit (often caused by a pinched wire or a faulty sensor) can cause P2135. Disconnect the throttle body connector and the pedal sensor connector. Measure resistance between the 5V reference pins and ground at the ECM connector (pin 64 for TPS, pin 57 for APP). Resistance should be infinite. If you find a short, repair the harness. This is a common issue on Silverados where the harness rubs against the intake manifold or the firewall.
6. Inspect the ECM Grounds and Power Supply
   A poor ECM ground can cause false P2135 codes. Locate the ground splice pack under the hood near the battery (often on the driver’s side frame rail). Clean and tighten all ground connections. Check the ECM power fuses (Fuse 10 and Fuse 19 in the underhood fuse block). Voltage drop test the ground circuit: with the engine running, measure voltage between the ECM ground pin and the battery negative terminal—should be less than 0.1V. If it’s higher, repair the ground.
7. Perform a Throttle Relearn Procedure
   After any repair, you must relearn the idle and throttle position. For 2007-2013 Silverados: turn key ON for 30 seconds (do not start), then turn key OFF for 30 seconds. Start the engine and let it idle for 10 minutes without touching the accelerator. If you have a scan tool, use the “Throttle Relearn” function (typically requires 1.0 hour labor at a shop, or $50-$100 if you own a capable scanner).
8. Consider the ECM Itself (Rare but Possible)
   If all wiring, sensors, and grounds test good, the ECM may have an internal fault. This is uncommon on Silverados but happens. ECM replacement (GM part #12628496 for most 5.3L applications) requires programming by a dealership (labor 1.5-2.0 hours plus $150-$200 for programming). Do not attempt this until you have exhausted the previous steps.

Common Silverado-Specific Note: On 2014+ models (K2XX platform), the P2135 code is often caused by a faulty throttle body connector that loses pin tension. The fix is to replace the connector pigtail (GM part #13577712) and perform the relearn. Total cost: $15 for the connector, 0.5 hours labor. This saves you from replacing the entire throttle body.

Fix

This guide covers the dreaded P2135 code on GM Silverado trucks (typically 2007-2014 models with 4.8L, 5.3L, or 6.2L engines). This code indicates a Throttle/Pedal Position Sensor/ Switch ‘A’ / ‘B’ Voltage Correlation error. It often results in reduced power, limp mode, or a no-start condition. Below is a step-by-step diagnostic and repair process based on real-world success.

Important: Always disconnect the negative battery cable before working on throttle body or pedal wiring. Use a high-quality multimeter for testing.

Diagnostic & Repair Steps

1. 1. Verify the Code and Freeze Frame Data

   Scan the vehicle with a professional-grade scan tool (not a basic code reader). Record freeze frame data to see engine RPM, throttle position, and voltage readings at the time the code set. If you have multiple codes (e.g., P0121, P0222), focus on P2135 first.

   Labor estimate: 0.3 hours for scanning and data review.

2. 2. Inspect the Throttle Body Wiring Harness

   The most common cause on Silverados is chafed or broken wires at the throttle body connector (6-pin connector on the side of the throttle body). Look for wires rubbing against the intake manifold or engine cover. Common failure wires are the 5V reference (pin 2, dark green) and the low reference (pin 4, black/white).

   GM Part Number for throttle body connector pigtail: 13506714 (includes pins and seals). Cost: ~$25.

   Labor estimate: 0.5 hours to inspect and repair minor chafing.

3. 3. Test the Throttle Position Sensor (TPS) Signals

   With the key ON, engine OFF, backprobe the TPS signal wires at the throttle body connector. You should see two separate voltage signals: TPS ‘A’ (pin 3, yellow wire) and TPS ‘B’ (pin 5, purple wire). Both should read approximately 0.5V at idle (closed throttle) and rise to 4.5V at wide-open throttle. The difference between them should be less than 0.5V at any point.

   If one signal is stuck or erratic, replace the throttle body assembly. GM Part Number: 12679584 (for 5.3L/6.2L, 2010-2014). Cost: ~$180-$250.

   Labor estimate: 1.0 hour for testing and replacement.

4. 4. Check the Accelerator Pedal Position Sensor (APP)

   The pedal assembly has two internal sensors that must correlate. Test at the pedal connector (6-pin, under dash near the brake pedal). Pin 1 (5V ref, brown), pin 2 (signal A, dark blue), pin 3 (low ref, black), pin 4 (5V ref, gray), pin 5 (signal B, light green), pin 6 (low ref, black/white). With the pedal released, signal A should read ~0.5V, signal B ~0.3V. When fully depressed, signal A ~4.5V, signal B ~4.0V. If voltages are out of range or cross over incorrectly, replace the pedal assembly.

   GM Part Number: 25960714. Cost: ~$90-$120.

   Labor estimate: 0.5 hours for testing and replacement.

5. 5. Inspect the Ground Circuit

   A poor ground at the engine block or chassis can cause P2135. Locate the ground strap from the back of the driver-side cylinder head to the firewall. Clean the connection points with a wire brush and dielectric grease. Also check the G102 ground (under the air box) for corrosion.

   Labor estimate: 0.3 hours for cleaning and tightening.

6. 6. Perform a Throttle Body Relearn

   After any throttle body or pedal replacement, you must perform a throttle body relearn. Procedure: Turn key ON (engine OFF) for 30 seconds. Then turn key OFF for 30 seconds. Start the engine and let it idle for 10 minutes without touching the accelerator. If the idle is rough, drive the truck gently for 5-10 miles to complete the learn.

   Note: Some Silverados require a scan tool to perform the relearn. If the code returns after driving, you may need a professional scan tool to reset the TAC module.

7. 7. Replace the Throttle Actuator Control (TAC) Module (Last Resort)

   If all wiring, sensors, and grounds are good but the code persists, the TAC module (integrated into the ECM on many models) may be faulty. This is rare but possible. On 2007-2013 Silverados, the ECM must be programmed by a dealer or specialist. Part cost: ~$150-$200 for remanufactured ECM. Labor: 1.5 hours plus programming.

   Warning: Do not attempt this step without verifying all previous steps. Incorrect ECM replacement can lead to immobilizer issues.

Summary of Costs

• Throttle body replacement: $180-$250 (part) + 1.0 hour labor
• Pedal assembly replacement: $90-$120 (part) + 0.5 hour labor
• Wiring repair: $25 (pigtail) + 0.5 hour labor
• ECM replacement: $150-$200 (part) + 1.5 hours labor + programming fee (~$100)

Final Note: The P2135 on Silverados is almost always a wiring or connector issue at the throttle body. Start there before replacing expensive parts. If the code returns after a repair, recheck the pedal and ground circuits. Good luck, and drive safe.