Chevrolet P1516 Code: Throttle Actuator Position Performance (TAC)
The electronic throttle didn't move to where the computer commanded, so the engine drops into Reduced Power.
At a glance
Severity: Moderate
- Meaning
- Throttle Actuator Position Performance (TAC)
- System
- Speed & Idle Control · Powertrain
- Safe to drive?
- With caution
- Typical repair cost
- $10–$1,100
- DIY difficulty
- Moderate
Chevrolet trucks and SUVs with electronic throttle control, such as V8 Silverado, Tahoe and Suburban models from the early 2000s on and the Trailblazer and Colorado, drive the throttle plate with a small electric motor. A throttle actuator control (TAC) function, a separate TAC module on early trucks and built into the engine computer later, compares the commanded throttle angle with the two throttle position sensors in the throttle body. P1516 sets when the actual position doesn't track the commanded position, or keeps hunting, for longer than about a second. For safety the system then limits throttle opening and shows 'Reduced Engine Power'. Carbon buildup that makes the plate stick, a worn throttle body motor or gear set and loose connector pins at the throttle body account for most cases.
Can I keep driving? The engine may suddenly lose power or be limited to a fast idle, which is risky when merging or passing. Drive only as far as needed to reach a safe place or a shop, and don't tow with this code active.
How to read P1516
- P Powertrain
- 1 Manufacturer-specific
- 5 Speed, idle & inputs
- 16 Specific fault
Symptoms
- 'Reduced Engine Power' message and very limited acceleration
- Engine stuck near idle or a fixed rpm regardless of pedal
- Surging, hunting or unstable idle
- Stalling when coming to a stop
- Check engine light, sometimes clears after a restart and comes back later
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Carbon and sludge buildup around the throttle plate causing it to stick or lag
- Worn throttle body motor, gears or internal position sensors
- Loose, spread or corroded pins at the throttle body connector
- Low or unstable system voltage (weak battery, bad grounds, failing alternator)
- Harness damage between the throttle body and TAC module or ECM
- TAC module or ECM fault, or software needing an update
Diagnosis step by step
Record all codes and freeze frame
Read codes from the engine computer and note companion codes. P1516 with throttle position correlation codes points toward the throttle body; with voltage-related codes, check the battery and charging system first.
Tools: OBD-II scanner
Check battery and grounds
The battery should rest near 12.6 V and the charging voltage should be 13.5–14.5 V. Inspect the engine-to-body and battery ground cables; voltage dips can make the throttle motor lag.
Tools: Multimeter
Inspect and clean the throttle body
With the ignition off and the key out (the plate can snap shut when powered), remove the intake duct and look for a black carbon ring behind the plate. Clean it with throttle body cleaner on a rag and open the plate gently by hand; don't force the gears.
Tools: Gloves, Screwdriver
Check the connector and harness
Unplug the throttle body connector, check for spread or corroded terminals, and wiggle the harness while watching the throttle position values on the scan tool with key on. Any dropouts point to the wiring.
Tools: Flashlight, OBD-II scanner
Compare commanded and actual throttle
With the engine off and key on, slowly press the pedal and watch TP sensor 1 and 2: they should move smoothly and in opposite directions or at a fixed ratio, without jumps. Sticking, flat spots or a mismatch with the pedal command confirm a failing throttle body.
Tools: OBD-II scanner
Relearn idle and road test
After cleaning or replacing the throttle body, clear the codes, leave the key on for about 30 seconds, then start and idle for a few minutes without touching the pedal so the idle position is relearned. Test drive, including light and wide-open throttle.
Tools: OBD-II scanner
Where the parts are
- 1Battery
- 2Alternator
- 3Engine computer (ECM)
- 4CAN bus
- 5Transmission
- 6Wheel speed sensor
- 7High-voltage battery
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Clean throttle body and relearn idle | Yes | $10–$150 |
| Repair throttle body connector pins or harness | No | $80–$300 |
| Replace electronic throttle body (DIY) | Yes | $180–$450 |
| Replace electronic throttle body (shop) | No | $350–$750 |
| Replace and program TAC module or ECM | No | $400–$1,100 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Emissions / smog test impact
Will fail
P1516 keeps the check engine light on, so the vehicle fails a US OBD emissions test; clear it after the repair and let the monitors complete before testing.
Frequently asked questions
Can I just clean the throttle body?
Often yes, if carbon is making the plate stick. If P1516 comes back soon after a thorough cleaning, the motor or gears inside the throttle body are likely worn and the unit should be replaced.
Why does my truck go into Reduced Engine Power?
When the computer can't trust where the throttle is, it limits throttle opening to prevent unintended acceleration. It's a protective mode, not a sign that the engine is damaged.
Is it the gas pedal sensor?
Pedal sensor faults usually set their own codes (for example P2138 for pedal sensor correlation). P1516 is about the throttle body not following commands, so start at the throttle body.
Does a new throttle body need programming?
Typically no programming, but an idle relearn is required: clear codes, key on for about 30 seconds, then start and idle without touching the pedal. Some vehicles may need a scan tool procedure.
Sources
- Manufacturer public service information (cross-checked)
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