What does it mean?
This generic powertrain/engine diagnostic code generally applies to turbocharged and supercharged engines, including but not limited to certain Ford, Mercedes, and Subaru vehicles.
The Powertrain Control Module (PCM) controls the boost pressure in a gasoline or diesel engine by managing the output circuit to the “B” wastegate/boost control solenoid.
Whenever there is an issue with the total boost range or engine performance that cannot be attributed to other circuit failures, the PCM will set the P0248 code. This code can indicate an electrical circuit fault or a mechanical engine problem, depending on the specific issue.
Troubleshooting steps may vary depending on the manufacturer, the type of wastegate/boost pressure control, and the color of the control solenoid wires.
Symptoms
Symptoms of a P0248 engine code may include:
Malfunction indicator light illuminated
Instrument cluster message alerting the driver to the condition
Lack of power
Causes
Possible causes for this code being set include:
Open in the control circuit (ground circuit) between the wastegate/boost control solenoid B and the PCM
Open in the power supply circuit between the wastegate/boost control solenoid B and the PCM
Short to ground in the power supply circuit of the wastegate/boost control solenoid B
Short to power in the power supply circuit of the wastegate/boost control solenoid B
Wastegate/boost pressure control solenoid B
Possibly a failed PCM (highly unlikely)
Diagnostic and Repair Procedures
A good starting point is always to check the Technical Service Bulletins (TSBs) for your specific vehicle. Your issue might be a known problem with a published fix from the manufacturer, which could save you time and money during diagnosis.
Next, locate the “B” wastegate/boost control solenoid on your specific vehicle. Once located, visually inspect the connectors and wiring. Look for scratches, rubbing, exposed wires, burns, or melted plastic. Separate the connectors and carefully inspect the terminals (the metal parts) inside the connectors. Check if they appear burnt or have a greenish tint indicating corrosion. Use electrical contact cleaner and a plastic bristle brush if terminal cleaning is necessary. Allow it to dry and apply electrical grease where the terminals make contact.
The most common failure is due to electrical/vacuum connection issues.
If you have a scan tool, clear the diagnostic codes from memory and see if P0248 returns. If it doesn’t, the connections were likely your problem.
If the code returns, we will need to test the solenoid and its associated circuits. Typically, there are 2 wires to the wastegate/boost control solenoid. First, disconnect the wiring harness going to the wastegate/boost control solenoid. With a digital multimeter set to ohms (DVOM), connect one lead of the multimeter to one terminal of the solenoid. Connect the remaining multimeter lead to the other terminal of the solenoid. It should not be open or shorted. Check the resistance specifications for your specific vehicle. If the solenoid is open or shorted (infinite resistance or no resistance/0 ohms), replace the solenoid.
If this test passes, use a DVOM to ensure you have 12V at the power supply circuit of the wastegate/boost control solenoid (red lead to the solenoid power circuit, black lead to a good ground). Make sure the ignition is on. If there is no 12 volts at the solenoid, or if there is 12 volts when the ignition is off, repair the wiring from the PCM or relay to the solenoid, or possibly a faulty PCM.
If that checks out, verify that the wastegate/boost control solenoid is properly grounded. Connect a test light to the 12V battery positive (red terminal) and touch the other end of the test light to the ground circuit going to the wastegate/boost control solenoid circuit ground. Using the scan tool to activate the wastegate/boost control solenoid, check if the test light illuminates each time the scan tool activates the solenoid. If the test light does not illuminate, it would indicate a circuit problem. If it does light up, wiggle the wiring harness going to the solenoid to see if the test light flickers, indicating an intermittent connection.
Ensure all mechanical components are secured and functioning properly. Make sure that if vacuum is used, there is sufficient vacuum at the wastegate/boost control solenoid. Otherwise, locate the source of the vacuum blockage or leak.
If all tests have passed so far and you continue to get a P0248 code, it would most likely indicate a faulty wastegate/boost control solenoid, although a defective PCM cannot be ruled out until the solenoid has been replaced. If in doubt, seek assistance from a qualified automotive diagnostician. PCMs need to be programmed or calibrated to the vehicle to be installed correctly.