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2016 Traverse Stabilitrak Light, Reduced Engine Power, P0121

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Mike T. · rep 0 · May 25, 1:38 AM · 1 replies · solved · Question

Vehicle: 2016 Chevrolet Traverse LT

Hey everyone,

My 2016 Chevrolet Traverse LT with the 3.6L engine and about 110,000 miles is acting up. The 'Service Stabilitrak' light came on, followed by the 'Traction Control Off' light, and then a 'Reduced Engine Power' message. The car immediately lost power and felt very sluggish.

I was able to get it home, and when I scanned it, I got a P0121 code, which points to a Throttle Position Sensor / Pedal Position Sensor 'A' Circuit Range/Performance problem. Could this one code cause all those other warnings and reduced power?

What's the most likely culprit here? Is it usually the throttle body itself, or could it be the accelerator pedal position sensor? Any advice on how to confirm before I start replacing parts?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 1:38 AM

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ClearTheCode admin answer:

Your 2016 Chevrolet Traverse LT's symptoms – 'Service Stabilitrak,' 'Traction Control Off,' 'Reduced Engine Power,' and the P0121 code – are classic indicators of an issue with the electronic throttle control system. The P0121 code specifically points to a problem with the Throttle Position Sensor (TPS) or Accelerator Pedal Position Sensor (APP Sensor) 'A' circuit.

Understanding the System:

  • The APP sensor (on the accelerator pedal) tells the engine computer (ECM) how much throttle you're requesting.
  • The TPS (on the throttle body) tells the ECM the actual position of the throttle blade.
  • The ECM compares these inputs. If there's a discrepancy or a sensor reading is out of expected range, it triggers the 'Reduced Engine Power' mode to protect the engine and transmission, and disables Stabilitrak/Traction Control as a safety measure.

Common Causes for P0121:

  1. Faulty Throttle Body Assembly: This is a very common failure point. The TPS is often integrated into the throttle body. Carbon buildup on the throttle blade can also cause it to stick, leading to incorrect TPS readings.
  2. Faulty Accelerator Pedal Position (APP) Sensor: The sensor on the accelerator pedal itself can fail, sending incorrect signals to the ECM.
  3. Wiring Issues: Damaged, corroded, or loose wiring/connectors in the throttle control system (between the APP sensor, throttle body, and ECM).
  4. ECM Issues: Less common, but a faulty Engine Control Module could misinterpret sensor signals or have internal issues.

Diagnostic Steps:

  1. Visual Inspection: Check the wiring harness and connectors at both the throttle body and the accelerator pedal for any signs of damage, corrosion, or loose connections.
  2. Inspect Throttle Body: Remove the air intake tube and visually inspect the throttle blade for excessive carbon buildup. Clean it carefully with throttle body cleaner if necessary (avoid spraying directly into electrical components).
  3. Monitor Live Data (with a scanner): If you have access to a scanner that can read live data, monitor the APP sensor and TPS voltages/percentages while operating the pedal and observing the throttle blade. Look for smooth, consistent readings without drops or spikes.
    • APP Sensor: Should smoothly increase/decrease with pedal movement.
    • TPS: Should smoothly increase/decrease as the throttle blade opens/closes.
  4. Wiggle Test: While monitoring live data, gently wiggle the wiring harnesses for the APP sensor and throttle body. If the readings fluctuate, you likely have a wiring issue.

When to See a Shop:

  • If visual inspection and live data monitoring don't clearly identify the faulty component.
  • If you're uncomfortable performing the inspection or cleaning the throttle body.
  • If the issue persists after cleaning or if you suspect an internal throttle body or APP sensor failure, as replacement requires specific procedures and sometimes relearning by the ECM.
  • If you suspect ECM issues, which require specialized diagnostic tools.
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