The P0120 Mystery on Your 2022 Cadillac XT6
When your 2022 XT6 drops into "Reduced Engine Power" mode and the check engine light stares back at you, the case file opens on P0120 — a throttle position sensor circuit malfunction. Your three-row luxury crossover runs the 3.6L V6 (LGX) on GM's C1XX platform, sharing its powertrain DNA with the XT5 and Buick Enclave. The electronic throttle body's integrated TPS has sent voltage signals outside normal parameters, prompting the ECU to limit engine output as a safety precaution.
Evidence You'll Notice
- "Reduced Engine Power" warning on the display
- Check engine light illuminated
- Dramatic power reduction — the XT6 struggles to accelerate
- Throttle input feels disconnected from engine response
- Idle may be rough, hunting, or stalling
- May affect AWD system behavior
Ranked Causes
1. Electronic Throttle Body Failure
The ACDelco throttle body on the 3.6L V6 is the number-one suspect. Internal TPS potentiometer wear causes dead spots in the voltage sweep, triggering P0120. This is the same throttle body used across the C1XX platform (XT5, Enclave, Traverse).
2. Carbon Contamination
Direct injection blowby vapors coat the throttle bore over time. On a 2022 model with typical mileage, carbon buildup is a very common cause of throttle position reading errors.
3. TAC System Communication Error
The Throttle Actuator Control system can experience software glitches or CAN bus communication faults that generate P0120 without actual throttle body hardware failure.
4. Wiring or Connector Damage
Engine bay heat and moisture exposure can degrade the throttle body connector or harness wiring, causing intermittent or persistent TPS signal faults.
5. APP Sensor Degradation
The dual pedal position sensors can develop resistance issues, sending conflicting signals that the ECU logs as a throttle circuit malfunction.
Investigation Steps
- Scan for DTCs with a GM-capable scanner — look for TAC companion codes
- Inspect throttle body for carbon deposits and connector condition
- Monitor live TPS data — watch for dropouts during slow sweep from closed to open
- Check GM TSBs for C1XX platform throttle issues
- Verify APP sensor correlation with TPS readings
Cost Breakdown
- Throttle body replacement (ACDelco): $300–$600
- Throttle body cleaning + relearn: $175–$350
- TAC reprogram: $150–$300
- Wiring/connector repair: $100–$300
- APP sensor/pedal assembly: $175–$400
Can I Drive With P0120?
Not in traffic. The XT6 in Reduced Engine Power mode is barely mobile. If you have passengers (this is a three-row vehicle, after all), get everyone to safety and have it towed. Check your Cadillac warranty status — 2022 models within the 4-year/50,000-mile window are fully covered.
DIY vs Professional
Check warranty first. Out of warranty, the throttle body replacement is the same procedure as the XT5 and Enclave — accessible on top of the 3.6L V6. Requires TAC relearn with a GM-compatible scan tool. Carbon cleaning is a worthwhile first step at a lower cost.
Frequently Asked Questions
Is the XT6 throttle body the same as the XT5?
Yes. Both use the same 3.6L V6 (LGX) on the C1XX platform with identical ACDelco electronic throttle bodies. Parts are interchangeable.
Will P0120 damage the engine if I keep driving?
The Reduced Engine Power mode protects the engine from damage. However, the underlying fault should be repaired promptly — continued driving in limp mode puts stress on other systems.
How do I know if it's the throttle body or just carbon?
A mechanic monitors live TPS data while manually sweeping the throttle. If the voltage drops out at certain positions, the internal sensor has failed and replacement is needed. If the voltage is stable but the plate sticks, carbon cleaning will likely fix it.
Is P0120 related to the fuel system?
No. P0120 is specifically about the throttle position sensor circuit — it controls airflow, not fuel. However, a stuck throttle can cause secondary lean or rich running conditions.