P2135 on 2008-2011 Chevrolet Silverado 1500: Reduced Power Causes and Fixes

What's Unique About the 2008-2011 Chevrolet SILVERADO 1500

This is a very common problem on 2008-2011 GM trucks and SUVs built on the GMT900 platform. The issue was so widespread that General Motors issued a Technical Service Bulletin (TSB #11-06-04-007C) outlining a specific repair procedure. The TSB advises technicians *not* to replace the entire throttle body but instead to replace just the sensor cover and clips 🎬 Watch: How to replace the TPS sensor and perform a relearn. using a specific kit (GM P/N 19259452) and, on 2008-2010 models, reprogram the ECM. However, for many DIY mechanics and even shops, replacing the complete throttle body assembly is a more straightforward and reliable long-term repair.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Symptoms You May Notice

• "Reduced Engine Power" message on the dashboard.
• Check Engine Light is on.
• Severely limited acceleration (Limp Mode).
• Vehicle may hesitate or surge during acceleration.
• Engine may stall.
• Hard or erratic shifting as the transmission computer struggles with incorrect torque data.

Most Likely Causes

1. Failing Throttle Position Sensor (TPS) / Throttle Body Assembly 🔴 High Probability This is a well-documented failure point on this platform, as acknowledged by GM's own TSB. The two internal sensors, which are integrated with the throttle body, are known to fail or send conflicting signals due to wear and heat cycling.
   How to confirm: Use an OBD-II scanner to monitor live data for 'TP Sensor 1' and 'TP Sensor 2'. With the key on and engine off, slowly press the gas pedal. TP Sensor 1 voltage should sweep smoothly from approximately 0.5V to 4.5V. TP Sensor 2 should do the inverse, sweeping from ~4.5V to ~0.5V. Any jumps, dropouts, or signals that don't move in a smooth, opposing manner point to a faulty throttle body.
   Typical fix: Replace the entire throttle body assembly. While a TSB exists for replacing just the sensor cover (GM P/N 19259452), the complete assembly is more readily available and ensures all related components (motor, sensors, gears) are new, providing a more reliable fix. A throttle relearn procedure is required after replacement.
   Est. part cost: $150-$350
2. Wiring Harness or Connector Issue 🟡 Medium Probability The wiring harness connector at the throttle body is exposed to engine heat and vibration. This can lead to 'fretting corrosion' on the terminal pins, loose pins, or internal wire breaks within a few inches of the connector, which are not always visible.
   How to confirm: Visually inspect the throttle body connector and nearby wiring for any signs of damage, corrosion, or loose-fitting pins. With the engine running, carefully wiggle the harness near the connector to see if it triggers the 'Reduced Power' mode or causes the engine to stumble. This 'wiggle test' is a key diagnostic step.
   Typical fix: Repair the damaged section of wiring or, more commonly, replace the connector pigtail (e.g., ACDelco PT2713). Clean the throttle body pins with electrical contact cleaner and apply dielectric grease to the new connector to prevent future corrosion.
   Est. part cost: $15-$50

Rare But Worth Checking

• Outdated ECM Software: GM's TSB #11-06-04-007C specifically calls for an ECM software update on 2008-2010 models after replacing the TPS cover. This suggests the original software logic was too sensitive to minor sensor deviations. If you've replaced the throttle body and the problem persists, a software update at a dealership might be the final step.
• Faulty Engine Control Module (ECM): This is very rare. Before condemning the ECM, all other possibilities, especially the throttle body and wiring, must be exhaustively ruled out. An ECM failure is unlikely to only manifest as a P2135 code.

Diagnosis Steps

1. Read the code with an OBD-II scanner and confirm P2135 is present, checking for any other related codes like P1516, P0120, or P0220.
2. Turn the ignition off. Visually inspect the electrical connector at the throttle body for corrosion, damage, or backed-out pins.
3. Inspect the wiring harness leading to the throttle body for any visible damage, chafing, or melting. Pay close attention to the first 4 inches of wiring from the connector.
4. With the engine running, perform a 'wiggle test' by carefully moving the wiring harness near the throttle body connector. If this induces the fault, the wiring or connector is the problem.
5. If wiring looks good, use a scan tool to observe the live voltage data from TP Sensor 1 and TP Sensor 2. With the key on and engine off, the values should be steady.
6. Slowly press the accelerator pedal to the floor and release it. TP Sensor 1 should sweep smoothly from ~0.5V up to ~4.5V, and TP Sensor 2 should sweep smoothly from ~4.5V down to ~0.5V. If one or both signals are erratic, jumpy, or flat, the throttle body assembly has failed.
7. If sensor data and wiring are perfect, the issue could be a rare ECM fault or require a software update per TSB 11-06-04-007C, especially on 2008-2010 models.

Parts You'll Likely Need

• Throttle Body Assembly (OEM #ACDelco 217-3156 (may be superseded by GM 12670839, but verify VIN as 12670839 fits other engines).) — This is the most common cause of P2135. The throttle position sensors are integrated into the assembly, and replacing the whole unit is the most reliable fix.
  Trusted brands: ACDelco (OEM), Bosch, Hitachi, Dorman
  OEM price range: $240-$365
  Aftermarket price range: $150-$250
• Throttle Position Sensor Kit (OEM #GM 19259452) — This is the specific kit called for in TSB #11-06-04-007C to replace only the sensor cover and clips. It is a viable, lower-cost alternative to a full throttle body replacement if you are comfortable with the more detailed procedure.
  Trusted brands: ACDelco (OEM)
  OEM price range: $50-$100
  Aftermarket price range: $40-$70

Related Codes That Often Appear With This One

• P1516: A GM-specific code for 'Throttle Actuator Control (TAC) Module Throttle Actuator Position Performance'. It often appears with P2135 as they both relate to the PCM's ability to control and verify the throttle's position.
• P0120 / P0220: General fault codes for TPS Sensor 'A' or 'B' circuit malfunction. They can accompany P2135 if one of the sensors has a hard failure in addition to the correlation issue.

Technical Service Bulletins (TSBs) & Recalls

• Bulletin #11-06-04-007C: Addresses a 'Reduced Engine Power' message and DTC P2135 by providing a procedure to replace the throttle position sensor cover (P/N 19259452) and, for 2008-2010 years, reprogram the ECM.
• Bulletin #PIP3089B: Addresses P2135 and other throttle codes caused by bad terminal crimps or broken wires within the harness near the throttle body connector.

Platform-Specific Known Issues

• A GM Technical Service Bulletin (TSB #11-06-04-007C) was issued for this exact problem. It provides a procedure for replacing only the throttle position sensor cover and clips (GM P/N 19259452), rather than the entire throttle body.
• For 2008-2010 models, the TSB also requires an ECM software update after the repair. 2011 models do not require this update.
• GM also had a special coverage adjustment (#11273A, 10 years/120,000 miles) for this issue, but it has since expired for all affected vehicles.
• Another TSB (PIP3089B) points to bad terminal crimps or broken wires inside the insulation near the throttle body connector as a potential cause.
• Throttle Relearn Procedure (No Tools): After replacing the throttle body, a relearn is needed. A common method is: 1. Start the engine and let it idle in Park for 3 minutes. 2. Turn the engine off and wait 60 seconds. 3. Start the engine again and let it idle in Park for another 3 minutes. 4. Turn the engine off and wait 60 seconds. The idle should now be stable.

Mechanic-Grade Diagnostic Values

• Throttle Actuator Control (TAC) Motor Resistance — expected: 2 to 15 Ohms. Failure: A reading over the limit indicates an open circuit; a reading under 1 Ohm indicates a short circuit.
• TPS1 Resistance Sweep (between pins D and E) — expected: Starts at ~2.7 kOhms (closed) and smoothly increases as throttle opens.. Failure: Resistance does not change, or has sudden gaps/spikes during the sweep.
• TPS2 Resistance Sweep (between pins E and F) — expected: Starts at ~2.2 kOhms (closed) and smoothly decreases as throttle opens.. Failure: Resistance does not change, or has sudden gaps/spikes during the sweep.
• 5V Reference Voltage at TB Connector (Key On, Engine Off) — expected: 5.0 Volts. Failure: Significantly lower or no voltage indicates a wiring or ECM issue.

Scan Tool Commands That Help

• Tech 2 / GDS2: ECM Reprogramming (using SPS) — Required on 2008-2010 models after performing the TPS cover replacement outlined in TSB 11-06-04-007C to update the software logic.
• Professional Scan Tool: Idle Learn Reset / Throttle Learn — Used after replacing the throttle body or cleaning it to reset the learned idle values in the ECM. Some scanners may list this under engine-specific functions.

Wiring & Ground Locations

• G103 — On the front of the right (passenger side) cylinder head.. This is a primary engine ground. A poor connection here can cause erratic sensor readings and is a known, though often overlooked, cause of P2135.
• G106 — On the right rear of the engine block.. Another critical engine ground point. Corrosion or a loose connection can lead to intermittent electronic issues, including throttle control faults.
• Throttle Body Connector — The 6-pin electrical connector on the throttle body assembly.. This is the direct interface for the TPS sensors. Pin E (Gray) is 5V Reference, Pin D (Dark Green) is TPS1 Signal, and Pin F (Purple) is TPS2 Signal. Knowing the pinout allows for direct testing of the harness and sensor signals.
• Underhood Fuse Block — In the engine bay, on the driver's side.. Contains fuses critical for the Engine Control Module (ECM), specifically fuses 4, 5, 12, and 56, which power the control circuits for the throttle system.

Real Owner Repair Stories

• Chevrolet Forum user '2012_Silverado' (2012 Chevrolet Silverado, 45,000 miles) — Truck started to jump/shut off while driving, 'reduced engine power' message appeared, Check Engine Light on with code P2135.
  ❌ Tried (didn't work) The user was skeptical that the initial fix would last.
  ✅ What actually fixed it A mechanic first performed a software update. The user noted that common causes discussed by other owners included loose terminal connections at the throttle body, corroded grounds on the cylinder heads (G103/G106), and harness damage, indicating these are the primary areas to investigate if the software update does not hold.

"I Checked Everything" — The Actual Cause

• While P2135 is an electrical code not typically diagnosed with a smoke test, the equivalent scenario is when all components seem to test correctly. In these cases, the root cause is often an issue that passes a simple bench test or wiggle test. This can include a corroded main engine ground (G103/G106) that only causes issues under electrical load, or a short to ground in a completely different sensor that shares the same 5-volt reference circuit as the throttle position sensors.

OEM Part Supersession History

• ACDelco 217-3156 → GM 12601387 / ACDelco 217-3153 (Verify by VIN) — Part updates and redesigns.
  Heads up: The part number 12670839, sometimes cited, is incorrect for the V8 engines in this truck; it fits other GM vehicles with different engines like the 2.5L I4. Using the wrong throttle body can result in incorrect performance and persistent codes. Always verify the part number with the vehicle's VIN.

Model Year Variations Within This Range

• 2008-2010 vs 2011: Per TSB #11-06-04-007C, 2008-2010 models MUST have the ECM reprogrammed after the TPS cover repair, whereas 2011 models do not. This implies the 2011 models already contain the updated software with a less sensitive logic for detecting TPS correlation faults.