Code
P1516
OLDSMOBILE
P — Powertrain
Throttle Actuator Control TAC Module Throttle Actuator Position Performance
AI status
Completed
Completed
100%
Causes
- Faulty electronic throttle body (throttle actuator/motor or throttle position sensor)
- Faulty TAC/PCM module or internal control circuit
- Open, shorted, damaged or corroded wiring/connectors between PCM, TAC module, sensors, or accelerator pedal position sensor
- Low battery voltage or poor battery/ground connections
- Contaminated or sticking throttle plate (carbon buildup)
- Failed accelerator pedal position (APP) sensor or disagreement between APP and TPS
Symptoms
- Check Engine MIL illuminated
- Reduced engine power / limp-in mode
- Hesitation, surging or poor throttle response
- Unstable or high/low idle
- Engine may stall at idle or during deceleration
- Possible inability to accelerate normally
What to check
- Read and record stored and pending DTCs and freeze frame data with a capable scanner
- Capture live data: commanded throttle position, actual throttle position (TPS/angle), APP/pedal sensor values, motor duty/command, battery voltage
- Visual inspection of throttle body, connectors, wiring harness for damage, corrosion, or looseness
- Check battery voltage and main engine grounds with engine cranking and during throttle actuation
- Perform key ON engine OFF throttle self-test and watch for proper movement and sensor feedback
- Check for related communication errors on CAN/BUS if applicable
Signal parameters
- Throttle position sensor / angle: should move smoothly from closed (~0°/low voltage) to open (high voltage) and match commanded position trend
- TPS/APP voltages: typical closed-to-open range ~0.3–4.5 V (varies by vehicle); dual sensors should correlate and not be equal (redundant signals with different slopes)
- Commanded throttle (PCM target) vs actual throttle (measured): should track within a few degrees/percent under normal conditions
- Motor duty cycle / PWM: varies with command; expect actuator to command movement when a change in target position is requested
- Battery voltage: stable above ~12.4 V at key ON and above ~12 V while cranking; gross drops can affect actuator performance
Diagnostic algorithm
- Connect a scan tool capable of capturing PCM throttle PIDs. Record freeze frame and live data for commanded throttle, actual throttle angle, TPS1/TPS2, APP sensors, motor duty, and battery voltage.
- Inspect connectors and wiring at the throttle body and PCM for corrosion, bent pins, pushed-out terminals, or damage. Wiggle harness while watching live data for intermittent changes.
- Verify battery state-of-charge and main engine ground integrity. Retest with good battery or battery support if voltage low.
- With key ON / engine OFF, command throttle open/close using scan tool. Observe throttle plate movement and sensor feedback for smooth operation and correct correlation with commanded values.
- If throttle plate is slow, noisy, or sticks, remove and inspect throttle body for carbon deposits or mechanical binding. Clean if necessary following OEM procedure and retest.
- Check resistance/voltage of APP and TPS sensors per vehicle wiring diagram and compare to specifications. Verify dual sensor correlation and plausibility.
- If wiring and sensors check good, consider bench-testing or swapping a known-good throttle body/TAC module where possible, or replace the throttle body assembly per OEM guidance.
- After repair or replacement, perform any required relearn/idle learn and clear codes. Test drive and verify commanded vs actual throttle tracking and that P1516 does not return.
- If fault persists, investigate PCM/TAC module internal faults and vehicle-specific communication faults or software updates with OEM-level scan tool.
Likely causes
- Throttle body actuator motor failure or internal encoder issue
- Wiring harness damage at the throttle body connector (chafing, pin corrosion)
- Poor battery/ground causing voltage drop during actuator movement
- TPS/angle sensor drift causing discrepancy vs commanded position
- Throttle plate mechanical binding from deposits
Fault status
Status
PCM detected throttle actuator position does not follow commanded position (TAC module performance fault).
Repair difficulty: Medium
Diagnostic time: 1.5-3.0 hours
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