P1516 on 2014-2018 Chevrolet Corvette: Throttle Control Faults and Fixes

What's Unique About the 2014-2018 Chevrolet CORVETTE

For the C7 Corvette, the P1516 code is often associated with the vehicle entering 'Reduced Engine Power' mode, which also disables the traction control system because the computer can no longer trust its ability to manage engine torque. A Technical Service Bulletin (TSB) notes that this and related throttle codes can appear on higher mileage vehicles, suggesting wear and tear on the throttle body components is a key factor. Additionally, intermittent wiring faults, including wires breaking inside the insulation near the throttle body connector and poor grounding paths, are well-documented weak points on many GM vehicles, including the Corvette.

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 displayed on the dash.
• Check Engine Light is on.
• Severely limited throttle response and poor acceleration.
• Unstable or rough idle.
• Engine may stall or be difficult to start.
• Traction control system is disabled.
• Vehicle may buck or surge.

Most Likely Causes

1. Faulty Throttle Body Assembly 🔴 High Probability → Shop Fuel Injection Throttle Body The TSB for this model range suggests that throttle body issues can arise on high-mileage vehicles, indicating a potential wear item for the internal motor or position sensor.
   How to confirm: Use a scan tool to monitor commanded vs. actual throttle position. If the actual position is erratic, sticks, or doesn't follow the command, the throttle body is likely faulty. A static resistance test on the throttle body motor can also confirm an internal failure.
   Typical fix: Replace the entire throttle body assembly. After replacement, a 'Throttle/Idle Learn' procedure must be performed. It is highly recommended to use an OEM ACDelco part.
   Est. part cost: $150-$350
2. Wiring or Connector Issue 🟡 Medium Probability GM service information highlights that wires can break *inside the insulation* with no visible external damage, typically within 4 inches of the throttle body connector 🎬 Watch: How to diagnose and solve these mystery throttle codes., due to engine vibration and heat cycles.
   How to confirm: Visually inspect the connector for corrosion or backed-out pins. Perform a 'wiggle test' on the harness while monitoring throttle position data on a scan tool to see if the fault can be induced.
   Typical fix: Repair the broken wire(s) or replace the throttle body connector pigtail.
   Est. part cost: $20-$50
3. Dirty or Obstructed Throttle Body ⚪ Low Probability → Shop Fuel Injection Throttle Body Per TSB PIP4578B, carbon buildup from the PCV system can accumulate behind the throttle plate. The ECM learns to compensate, but if the throttle body is cleaned without an idle relearn, the existing compensation can cause this code. Incorrect reassembly after a deep cleaning can also cause the plate to bind.
   How to confirm: Remove the air intake tube and visually inspect the throttle bore and plate for significant carbon buildup. If the code appeared immediately after a cleaning, check that the throttle plate moves freely and is perfectly centered.
   Typical fix: Clean the throttle body bore and plate carefully with a dedicated throttle body cleaner and a soft cloth. Do not spray cleaner directly into the electronic components. Crucially, perform a 'Throttle/Idle Learn' procedure with a scan tool or manual process after cleaning.
   Est. part cost: $5-$15

Rare But Worth Checking

• Poor Engine or Body Grounds: A corroded or loose ground strap between the engine, body, or near the PCM can cause a slight voltage drop in the throttle control circuit, triggering P1516 intermittently. This is a well-documented issue on GM trucks sharing this architecture. The fix is often to clean all main ground points (like G101, G103, G105, G106) or add redundant ground wires from the battery negative to the throttle body, firewall, and PCM mounting points.
• Aftermarket Component Mismatch: Installing a larger-bore aftermarket throttle body or a plug-in throttle controller without a proper corresponding engine tune can cause this code. The ECM's expected throttle position voltage may not match the new readings from the modified hardware, triggering a fault.
• Faulty Powertrain Control Module (PCM): This should only be considered after all other possibilities, including wiring, grounds, and the throttle body itself, have been definitively ruled out. PCM failure is very rare.

Diagnosis Steps

1. Retrieve all stored DTCs with a capable scan tool. Note any other codes that appear alongside P1516.
2. Observe freeze-frame data to see the conditions under which the code was set.
3. Using the scan tool's live data function, monitor 'Commanded Throttle Position' and 'Actual Throttle Position'. The values should closely mirror each other as you slowly press and release the accelerator pedal (with the engine off, key on).
4. Inspect the throttle body electrical connector for loose pins, corrosion, or damage.
5. Gently wiggle the wiring harness leading to the throttle body, especially within the first 4 inches of the connector, while observing live data to see if the 'Actual Throttle Position' reading becomes erratic.
6. Inspect major ground points. Check the main battery-to-chassis ground, chassis-to-engine block ground strap (G101, G106), and any grounds near the PCM (G103) for looseness or corrosion.
7. Remove the air intake duct and visually inspect the throttle plate for heavy carbon buildup or any foreign objects that could cause it to bind.
8. If wiring and grounds are good and the throttle body is clean but the position data is still incorrect or unresponsive, the throttle body assembly is the most likely culprit. A static resistance test of the internal motor 🎬 See this walkthrough of the 5 most common P1516 fixes. can provide final confirmation.
9. After any repair, clear the codes and perform a 'Throttle/Idle Learn' procedure as specified by the service manual or a common manual procedure.

Parts You'll Likely Need

• Throttle Body Assembly (OEM #12740727 (supersedes 12678223)) — This is the most frequent point of failure. The internal motor or position sensor wears out, causing the P1516 code. The entire assembly is replaced as a single unit.
  Trusted brands: ACDelco (OEM)
  OEM price range: $250-$400
  Aftermarket price range: $150-$250
• Throttle Body Connector Pigtail (OEM #19352911 (supersedes 13581267)) — If a wiggle test confirms a wiring issue right at the connector, replacing the pigtail is the standard repair. The wires often break internally from vibration.
  Trusted brands: ACDelco, Dorman
  OEM price range: $30-$50
  Aftermarket price range: $20-$40

Related Codes That Often Appear With This One

• P2101 — This code, 'Control Module Throttle Actuator Position Performance', is very similar to P1516 and often appears with it, indicating a general fault in the throttle actuator's function.
• P2119 — Indicates an issue with the throttle body's ability to close properly, which can be caused by the same mechanical or electrical faults that trigger P1516.
• P0068 — This code indicates a correlation error between the MAP sensor, MAF sensor, and the throttle position. A faulty throttle body giving incorrect position data can cause this conflict.
• P2176 — This code means the PCM has not learned the throttle body's minimum position (idle). It often appears after a throttle body has been cleaned or replaced and the required idle learn procedure has not been completed.

Technical Service Bulletins (TSBs) & Recalls

• PIP4578B: Mentions that DTCs P1516, P0068, P0121, P2101, P2119, and/or P2176 may be experienced on high mileage vehicles. It details how carbon buildup alters throttle angle and explains that cleaning without an idle reset can cause faults.

Platform-Specific Known Issues

• A known issue involves intermittent electrical connection problems within the wiring harness near the throttle body, where wires break inside the insulation with no outward signs of damage.
• Per TSB #PIP4578B, this code, along with others like P2101 and P2176, may be experienced on high-mileage vehicles due to carbon buildup. Cleaning the throttle body without performing an idle relearn can also trigger the code.
• Modified vehicles with larger aftermarket throttle bodies or simple plug-in throttle controllers are known to trigger P1516 if the vehicle's tune is not adjusted to account for the different airflow and sensor voltage characteristics.

Mechanic-Grade Diagnostic Values

• Throttle Position Sensor (TPS) 5V Reference Voltage — expected: 5 Volts. Failure: Voltage significantly lower or higher than 5V indicates a problem with the ECM or wiring.
• Throttle Actuator Control (TAC) Motor Voltage — expected: Approximately 12 Volts on each of the two motor wires (Key On, Engine Off).. Failure: Lack of 12V power points to a wiring or ECM driver issue.

Scan Tool Commands That Help

• GM GDS2 (Global Diagnostic System 2): Module Diagnosis > Body Control Module > Bi-directional Controls — To activate specific outputs like lights or relays to confirm the BCM is functioning, which can help rule out broader electrical issues when chasing an intermittent P1516.
• GM GDS2 / Professional Scan Tool: Special Function > Idle Learn Reset — This is the factory-recommended method to reset learned idle values after cleaning or replacing the throttle body. It is more reliable than manual procedures and is necessary to prevent codes like P1516 or P2176 from appearing post-service.
• Professional Scan Tool with Bi-Directional Control: Throttle Position Control / Actuator Test — Allows the technician to command the throttle plate to specific percentages (e.g., 10%, 25%, 50%) and compare it to the actual position reported by the sensors. This directly tests the functionality of the throttle body motor and sensors.

Wiring & Ground Locations

• G101 / G106 — G101 is on the lower front of the engine block. G106 is on the front center of the frame cross rail, under the crank pulley. They are often jumpered together.. These are primary grounds for the Engine Control Module (ECM). A poor connection here can cause erratic ECM behavior and various engine-related codes, including P1516.
• G103 — Located at the left rear of the engine compartment on the cowl, above the brake booster.. This ground serves the Body Control Module (BCM), Instrument Panel Cluster (IPC), and Data Link Connector (DLC). While not directly for the throttle, a bad ground here can cause communication errors and symptoms that mimic a throttle issue. It was specifically mentioned in service information for C/K trucks with similar P1516 issues.
• G105 — Located at the left front of the engine compartment, behind the cooling fan relays.. Grounds various front-end components. While less critical for the throttle itself, ensuring all major engine bay grounds are clean is a key step in diagnosing intermittent electrical faults.
• Throttle Body Connector (X183) — The 6-pin electrical connector directly on the throttle body assembly.. This is the direct interface for power and sensor signals. Wires are known to break internally within 4 inches of this connector. The pigtail part number is ACDelco PT2706 or GM 19352911.

Real Owner Repair Stories

• CorvetteForum user (2019 Corvette Z06) — Reduced Engine Power message and codes P1516 and P2101 immediately after cleaning the throttle body.
  ❌ Tried (didn't work) Ensuring all connections were tight., Clearing codes with an HP Tuners device.
  ✅ What actually fixed it The user purchased and installed a new OEM throttle body, which resolved the issue. The forum consensus was that buying critical electronic parts from non-OEM sources like Amazon is risky and that the original throttle body likely failed during the cleaning process.

OEM Part Supersession History

• 12678223, 12620263, 12713774, 12729495, 12733469 → 12740727 — Standard part evolution for reliability improvements or manufacturing changes by GM.
  Heads up: The latest part number, 12740727, is the correct 87mm OEM replacement for all 2014-2018 Corvette engines (LT1, LT4). Using older stock or unverified aftermarket parts is not recommended.
• 13581267 → 19352911 (Also sold as ACDelco PT2706) — Part number update for the throttle body connector pigtail.