Turbocharger Boost Sensor A Circuit High
P0238 indicates the turbocharger/supercharger boost sensor A is reading a voltage signal that is higher than the PCM expects. When this code sets, the engine computer ignores the actual boost pressure reading and substitutes a conservative default value, limiting boost delivery and dynamic fuel timing to prevent engine damage.
What You Might Notice
- Check engine light illuminated
- Reduced engine power and acceleration
- Lower than normal turbo boost pressure
- Rough idle or hesitation during acceleration
- Possible overboost condition if sensor signal is intermittent
Most Common Causes
- 1
Faulty boost sensor
The boost sensor itself is failing or providing an incorrect high voltage signal. This is the most common cause of P0238.
- 2
Wiring short to voltage
The boost sensor circuit wiring is shorted to battery voltage or another high voltage source, causing the PCM to read an abnormally high signal.
- 3
Intermittent wiring problems
Loose connectors, corroded terminals, or damaged wiring in the boost sensor circuit cause intermittent high voltage readings.
- 4
Faulty PCM or reference voltage issues
A malfunctioning PCM or problems with the 5-volt reference circuit can cause the sensor signal to be misinterpreted as too high.
How to Diagnose It
- 1
Check Faulty boost sensor — The boost sensor itself is failing or providing an incorrect high voltage signal. This is the most common cause of P0238.
- 2
Check Wiring short to voltage — The boost sensor circuit wiring is shorted to battery voltage or another high voltage source, causing the PCM to read an abnormally high signal.
- 3
Check Intermittent wiring problems — Loose connectors, corroded terminals, or damaged wiring in the boost sensor circuit cause intermittent high voltage readings.
- 4
Check Faulty PCM or reference voltage issues — A malfunctioning PCM or problems with the 5-volt reference circuit can cause the sensor signal to be misinterpreted as too high.
How to Fix It
- 1
Inspect and test boost sensor
Locate the turbocharger boost sensor and test it with a multimeter to verify it is reading within the normal voltage range (typically 0.5-4.5V). Replace the sensor if it is stuck at high voltage or reads out of specification.
- 2
Check wiring and connectors
Inspect the boost sensor wiring harness and connector for corrosion, loose pins, or damage. Clean corroded terminals and reseat connectors firmly. Look for any wires pinched or shorted against engine components.
- 3
Test 5-volt reference circuit
Use a multimeter to verify the PCM is providing the correct 5-volt reference signal to the boost sensor circuit. If voltage is incorrect, there may be a PCM fault or internal wiring issue.
- 4
Reprogram or replace PCM
If all sensors and wiring check out normal, the PCM may be faulty and require reprogramming or replacement. Have the PCM tested by a qualified technician before replacement.
Need a deeper diagnosis?
Search for related repair guides or browse by system.