Code
P0238
HUMMER
P — Powertrain
Turbocharger Boost Sensor Circuit High Voltage
AI status
Completed
Completed
100%
Causes
- Faulty turbocharger boost (MAP) sensor
- Short to battery/5V reference in sensor wiring
- Open or high-resistance ground for the sensor circuit
- Poor connector or corroded pins at sensor/ECM
- Damaged wiring harness (pinched, chafed, exposed)
- ECM/PCM internal fault (rare)
Symptoms
- Check Engine Light (MIL) on
- Reduced engine power, limp-home mode
- Poor drivability under boost (hesitation, surging)
- Unusual boost gauge readings (if fitted) — unusually high or pegged signal
- Reduced fuel economy
What to check
- Read freeze frame and live data with a scan tool to note engine speed, load, and boost voltage when the code set
- Visually inspect sensor, connector, and wiring for damage, corrosion, or water intrusion
- Backprobe sensor connector and measure reference voltage (should be ~5V) and ground continuity
- Measure sensor output voltage with key ON engine OFF and with engine running at idle and under boost
- Wiggle wiring and connector while watching live data to look for intermittent faults
- Disconnect the sensor and verify ECU reaction (some systems will set related codes or default values)
Signal parameters
- Reference (supply) voltage: ~5.0 V (typical) — must be stable
- Sensor output: generally 0.5–4.5 V proportional to manifold absolute pressure (exact range varies by vehicle)
- At key ON, engine OFF: output should be within manufacturer’s specified resting voltage (consult service manual)
- Under boost: output typically rises toward upper range (often >2.5 V) but must not exceed sensor max (~4.5 V)
- High-voltage fault means sensor output exceeds expected maximum or is shorted toward supply
Diagnostic algorithm
- Retrieve codes, freeze frame and live data with a scan tool. Note conditions when P0238 set (rpm, load, boost).
- Clear the code. Test drive to see if it returns and under what conditions.
- Perform visual inspection of harness and sensor connector for damage, corrosion, or water. Repair as needed.
- With ignition ON (engine OFF), backprobe the harness: verify stable ~5V reference and good ground continuity to chassis/ECM.
- Measure sensor output voltage at connector with key ON and engine running at idle. Compare to expected range. If output is > expected or pinned near supply, suspect short to 5V or bad sensor.
- With engine safely running, increase boost (road test or controlled load) and monitor sensor voltage. If voltage remains high/unresponsive, disconnect sensor and observe change in live data/engine behavior.
- If wiring shows intermittent or short to 5V, isolate by disconnecting at intermediate connectors or detach engine harness sections. Repair or replace damaged wiring and connectors.
- If wiring and connector are good but sensor output is out of range, replace the boost sensor and re-test.
- If problem persists after sensor and harness replacement, test/replace ECM only after confirming all inputs and grounds are correct.
- If code was caused by actual overboost (mechanical), inspect turbocharger wastegate, actuator, and boost control solenoid; repair as needed.
Likely causes
- Corroded sensor connector with short to 5V supply
- Sensor failed or producing excessive output
- Wire contacting a constant 12V source
- Bad ground at engine harness near sensor
- Wastegate or boost control stuck causing abnormal boost and sensor saturation
Fault status
Status
P0238 — Turbocharger Boost Sensor Circuit High Voltage: sensor output higher than expected or shorted to supply; check sensor, wiring, connector and reference/ground.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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