Code
P0068
HUMMER
P — Powertrain
Throttle Body Airflow Performance (PCM)
Views:
UK: 24
EN: 67
RU: 44
AI status
Completed
Completed
100%
Causes
- Contaminated or sticking throttle body plate or bore
- Faulty throttle body actuator (motor) or gear train
- Throttle position sensor (TPS) or accelerator pedal position sensor fault or poor correlation
- Mass air flow (MAF) sensor or manifold absolute pressure (MAP) sensor fault or contamination
- Vacuum leaks or intake air leaks upstream of throttle body
- Wiring harness damage, corrosion, or poor connector connections to throttle/TPS/MAF/MAP/PCM
Symptoms
- Check Engine Light (MIL) illuminated; P0068 stored
- Reduced engine power or vehicle enters limp/derate mode
- Erratic or high/low idle, surging, or stalling
- Delayed or poor throttle response
- Hesitation on acceleration, poor drivability
What to check
- Read freeze frame and full DTC list with a capable scan tool; note conditions when code set
- Observe live data: commanded throttle angle, actual throttle position, accelerator pedal position, MAF g/s (if equipped), MAP/kPa, RPM, fuel trims
- Check for additional related codes (TPS, pedal position, MAF, MAP, throttle actuator)
- Visually inspect wiring and connectors at throttle body, TPS/pedal sensors, MAF and PCM for damage, corrosion, or loose connections
- Inspect intake tract for vacuum leaks, cracked hoses, loose clamps, or unmetered air paths
- Perform a basic throttle body visual check for heavy carbon or sticking movement with ignition on (throttle should move according to commanded input)
Signal parameters
- Commanded throttle angle vs actual throttle plate angle — expected close correlation; difference >5° (or >10%) is suspicious
- Accelerator pedal position vs actual throttle position correlation — should track smoothly; significant lag or no correlation indicates sensor/actuator issue
- MAF airflow at idle (vehicle-specific) — compare to known-good baseline; unexpected low/high airflow can cause P0068
- Short-term and long-term fuel trims — values beyond ±10% suggest intake or measurement errors affecting airflow calculations
- MAP at idle should be stable for given engine and altitude; large deviations or noise indicate MAP/intake problems
Diagnostic algorithm
- Retrieve codes and freeze-frame data; record live data for throttle commanded vs actual, pedal position, MAF, MAP, RPM and fuel trims.
- Inspect wiring and connectors at throttle body, TPS/pedal sensor, MAF and PCM. Repair damaged wiring or poor connections. Clear codes and retest.
- Perform a smoke or smoke-equipment test and visual inspection to identify intake vacuum leaks; repair leaks and retest.
- Visually inspect throttle body for carbon deposits and free movement. With ignition ON (engine OFF) command throttle open/close with scan tool and verify smooth operation. If contaminated, perform throttle body cleaning per service manual and recheck.
- Verify pedal position sensor voltage/signal and TPS/accelerator sensor correlation using live data or bi-directional test. Replace faulty sensor if out of spec.
- Check MAF and MAP sensors: inspect, clean MAF with appropriate cleaner if contaminated, and test MAP sensor signal for stability and correctness.
- If wiring, sensors and throttle body clean/free and issue persists, perform throttle body adaptation/relearn procedure per manufacturer service information.
- If adaptation and repairs do not clear code, consider replacing the throttle body assembly (including actuator and integrated sensors). After replacement, perform required relearn/calibration.
- If multiple components replaced without resolution, suspect PCM or software; check for technical service bulletins (TSBs) and update PCM software before PCM replacement.
- After each repair step, clear codes, perform a road test and re-scan to confirm the fault is resolved.
Likely causes
- Carbon build-up causing throttle plate to stick or respond slowly
- Faulty throttle actuator or internal throttle body failure
- Poor TPS/accelerator pedal correlation or sensor drift
- Wiring or connector fault between throttle assembly and PCM
- Intake air leak or contaminated MAF causing incorrect airflow measurements
Fault status
Status
PCM detected throttle body airflow performance outside expected range — throttle/airflow response not matching commanded values.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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