Error Code P0238 is defined as Turbocharger/Supercharger Boost Sensor A Circuit High. It’s a generic trouble code which applies to all turbocharged vehicles. Vehicles of different manufacturer and model of course, have different definitions and specifications on troubleshooting and repair.

For generic vehicles for example, they call this error code Turbocharger/Supercharger Boost Sensor “A” Circuit High.

For GM vehicles, they call it Turbocharger Boost Sensor Circuit High Voltage.

For Dodge and Chrysler, it’s called MAP Sensor Signal Too High.

Some of the vehicle makes that can have this trouble code include, but are not limited to, Chrysler, Dodge, Mercedes, Volkswagen, Isuzu and Jeep.

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Definition

Error Code P0238 is set when the PCM (powertrain control module, also called as ECM or engine control module in some makes) detects an anomaly in the intake boost pressure sensor A input circuit, specifically open circuit or high voltage condition in the circuit.

The PCM delivers 5V as reference voltage signal to MAP sensor, while the MAP sensor sends variable voltage signal all the way back to the PCM. Thus, if the boost signal is high, the voltage signal is expected to be high, when the boost pressure is low, the voltage must be low as well. The PCM uses boost control solenoid to control the amount of pressure produced by the turbocharger, and simultaneously use the boost pressure sensor to verify the correct boost pressure. Zero boost sensor pressure means around 0.5V, while maximum boost is at 4.5V.

When the PCM sees boost pressure voltage higher than 4V during the time when there are no boost commanded, it triggers the Error Code P0238.

Common Symptoms

As with other error codes, Error Code P0238 activates the Check Engine light and ignores the sensor while substituting a generic value for actual boost pressure. When this happens, the PCM also simultaneously limits the amount of boost and dynamic fuel timing to a minimal amount. Other common symptom includes:

  • PCM turns the engine turbo boost off, causing lack of power during acceleration

Possible Causes

Error Code P0238 is caused by multiple factors, such as:

  • Defective boost sensor “A”
  • Intermittent wiring problems
  • Short circuit to voltage on sensor circuit
  • Defective PCM

How to Check

To check and diagnose for this error code, mechanics verify the problem and start by scanning and documenting the freeze frame data.

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Then, they clear the codes and check whether it comes back or not.

Next, they check the operation of boost pressure sensor signal and compare its performance to the MAP sensor and engine idle to see if they’re making the same readings.

Then, they will look for any signs of shorts to power in the harness through the turbo boost sensor connectors and wirings.

Next, they look for signs of corrosion in the turbo boost sensor connector, especially the pins, as corroded pins can cause shorting of power in the signal circuit.

Then, they will compare their readings to the specifications on sensor data scan.

How to Fix

This error code is pretty simple to fix. Two of the easiest solutions are:

  • Replacing internally shorted boost sensor, especially those that are not giving the right input pressure reading to the PCM
  • Repair shorts in the wiring harness
  • Secure harness from getting damaged
  • Replace damaged connectors that are causing shorts or open circuits
  • Replace internally shorted PCM, or repair the cause of the short

Short in the power source in sensor circuit can cause the PCM to burn internally if the circuit short is above 5V.

The vehicle may stall or not start at all if the PCM is burned.

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