P0242 — Turbocharger/Supercharger Boost Sensor B Circuit High

What P0242 means

P0242 is the standardized powertrain DTC for “Turbocharger/Supercharger Boost Sensor B Circuit High.” The code identifies the monitored condition; it does not by itself prove which part failed.

How to interpret the code wording

“Circuit High” means the module saw voltage or a signal above its calibrated range. Depending on circuit design, test for a short to voltage, an open/poor ground, an open signal circuit, terminal problems, or a failed sensor/actuator. Use the OEM wiring diagram because “high” does not identify the failed part by itself.

Possible symptoms

• Check Engine Light
• Low power or limp mode
• Abnormal boost response
• Possible smoke, whistle, or surge

Causes to test

These are diagnostic possibilities, not a statistical parts-replacement ranking. Vehicle-specific service information takes priority.

• Charge-air leak, loose clamp, split hose, or intercooler leak
• Wastegate/VGT/bypass actuator or control-solenoid fault
• Vacuum/pressure supply problem
• Boost/MAP sensor fault
• Turbocharger mechanical damage or restriction
• Exhaust restriction or control calibration issue

Step-by-step diagnostic workflow

1. Compare commanded boost with actual MAP/boost under controlled load.
2. Inspect charge pipes, clamps, intercooler, and vacuum/control hoses.
3. Test actuator movement and control solenoid duty/command according to service information.
4. Check boost/MAP sensor plausibility KOEO and under load.
5. Inspect turbocharger shaft/actuator/exhaust system only after control and leak checks.
6. Clear codes only after repair, then complete an appropriate drive cycle and verify the code and symptoms do not return.

Scan data worth checking

• Commanded vs actual boost/MAP
• Wastegate/VGT command
• MAF airflow
• Engine load and RPM
• Barometric pressure

Severity and drivability

Moderate to high. Severe overboost, underboost with smoke, or loss of power should be diagnosed before continued heavy-load operation.

Stop driving and investigate immediately if there is a flashing MIL, oil-pressure warning, overheating, fuel leakage, severe misfire, major loss of power, abnormal mechanical noise, or a transmission that is slipping badly.

Common diagnostic mistakes

• Replacing the turbo before pressure-testing the charge system
• Ignoring vacuum or actuator linkage faults
• Judging boost only from a dashboard gauge

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