P1516: How to Diagnose & Fix — Throttle Actuator Control (TAC) Module — Throttle Actuator Position Performance (GM)
4 vehicles · 2 makes · $120-$600 repair
How to diagnose and fix P1516: most-reported vehicles
Ranked by owner reports. Each card gives the symptoms, how to confirm the cause, the fix, parts and sources for that vehicle.
Buick Lucerne · 2006–2011
A failing electronic throttle body or throttle position sensor triggers a 'Reduced Engine Power' message and limp mode, with rough or surging idle and hesitant acceleration. The condition is common enough that GM issued a special coverage adjustment extending the throttle body warranty on some 2009-2011 cars.
Common Symptoms
- 'Reduced Engine Power' message
- Limp mode / very limited acceleration
- Rough or surging idle, RPM jumping
- Hesitation on acceleration
- Check engine light
How to Fix
Clean the throttle body first; if the TPS/electronic throttle body has failed, replace it and perform the required throttle relearn so the computer sets correct idle and full-throttle positions. GM Special Coverage extended this to 10 years / 120,000 miles on covered 2009-2011 models.
Sources for this issue (1)
Chevrolet Cobalt · 2005–2010
The Cobalt is drive-by-wire: the pedal module houses two redundant APP sensors, and the PCM compares them against the electronic throttle body's two TPS signals. When one signal drifts out of correlation the PCM drops the car into Reduced Engine Power mode — throttle authority is cut to a fast idle with the wrench/RE POWER message on the cluster, often with no warning in traffic. Owners report it as an intermittent that starts as a stumble and progresses to repeated limp events. P2138 (APP sensor 1-2 correlation) is the dominant code. The real cause is split between a worn pedal module, a dirty or failing electronic throttle body, and — very commonly on this car — corroded or loose connector terminals, since water intrusion down the A-pillar from a clogged sunroof drain reaches wiring in this area.
Common Symptoms
- "Engine Power Reduced" message on the cluster
- Sudden loss of acceleration in traffic
- Wrench warning light
- Rough or surging idle
- Intermittent hesitation that clears after a restart
How to Fix
Read the code before buying parts. Back-probe and inspect the pedal connector and the throttle body connector for green corrosion, spread terminals, or a loose lock — a bad terminal mimics a failed sensor and is the cheapest fix. If the terminals are clean, scope or graph both APP signals while sweeping the pedal to see which one drops out. A carbon-fouled throttle body responds to cleaning plus an idle relearn; if the fault follows the pedal, replace the accelerator pedal module (often cheaper than the throttle body and the more common culprit). Perform the throttle-position relearn after any replacement.
Sources for this issue (4)
Chevrolet Suburban · 2003–2007
The electronic (drive-by-wire) throttle system triggers a 'Reduced Engine Power' / 'Engine Power Is Reduced' limp mode that sharply limits acceleration and speed - dangerous when it strikes in traffic. The cause is usually the throttle actuator control (TAC): worn internal throttle-body sensors/motor, or a broken/chafed wire in the harness a few inches from the throttle-body connector. Correlation codes P2135 and TAC-performance code P1516 are typical.
Common Symptoms
- 'Reduced Engine Power' message and limp mode
- Sudden loss of acceleration
- Rough or surging idle
- Check engine light with throttle codes
How to Fix
Inspect the throttle-body connector and wiring first (the wires break near the plug); repair chafed wiring before replacing parts. If the throttle body itself is worn, replace it (GM 12570800 on 2003-2006 5.3L/6.0L trucks) and relearn the idle. Cleaning a carbon-fouled throttle body resolves milder cases. Some model years had extended special coverage on the accelerator-pedal/TAC system - check with a dealer.
Sources for this issue (1)
Chevrolet Tahoe · 2000–2010
Find P1516 by make
Browse every documented model and issue for your make.
P1516 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P1516 mean?
P1516 stands for "Throttle Actuator Control (TAC) Module — Throttle Actuator Position Performance (GM)." P1516 is a manufacturer-specific code used mainly by General Motors vehicles (Chevrolet, GMC, Buick, Cadillac, Hummer, Saturn), where it means the electronic throttle system's actual throttle plate position doesn't match what the computer commanded. In a drive-by-wire system, the ECM reads the accelerator pedal sensors and drives a motor on the throttle body to open the throttle; if the throttle position sensors report a position that disagrees with the command for more than about a second, this code sets. Drivers typically see a "Engine Power Reduced" message with the check engine light, and the vehicle drops into limp mode with sluggish, limited acceleration; some trucks set the code with no symptoms at all. Because throttle control directly affects your ability to accelerate, it should be diagnosed promptly rather than driven around. Note that the definition differs by manufacturer: Ford uses P1516 for an Intake Manifold Runner Control (IMRC) input error on Bank 1, while Honda/Acura use a throttle actuator position definition similar to GM's.
What are the most common causes of P1516?
The most common causes of P1516 are: Faulty throttle body / throttle actuator motor (the most common fix on GM trucks and SUVs), Dirty or carbon-fouled throttle body causing the throttle plate to stick or move erratically, Poor engine ground connections (corroded GM ground points G103/G104 causing voltage drop above 0.1V), Damaged wiring or corroded connectors in the TAC motor control or throttle position sensor circuits, Faulty throttle position sensor(s) on the throttle body, Failed stand-alone TAC module (separate module on 1999–2005 GM trucks), ECM/PCM fault, or a needed throttle relearn after cleaning or battery disconnect. The specific cause varies by vehicle.
How much does it cost to fix P1516?
Repair costs for P1516 range from $120 to $600, depending on the vehicle and root cause.
Which vehicles are affected by P1516?
Au7o has documented P1516 across 4 vehicle models from 2 manufacturers: Buick, Chevrolet.
Join 600+ people using Au7o to better understand their vehicles.
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.