Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Test Procedure
- A1 VERIFY THE ENGINE STARTS
Does the engine start?
Yes No For Transit, GO to A7.
For all others, GO to A6.GO to A2. - A2 CHECK THE VREF CIRCUIT FOR VOLTAGE
- Ignition OFF.
- MAP Sensor connector disconnected.
- Ignition ON, engine OFF.
- Measure the voltage between:
(+) MAP Sensor Connector, Harness Side (-) VREF Ground
Is the voltage between 4.5 - 5.5 V?
Yes No GO to A3. GO to PINPOINT TEST B . - A3 CHECK FOR VREF VOLTAGE AT THE SENSOR
- Ignition OFF.
- MAP Sensor connector connected.
- FRP Sensor connector disconnected.
- Ignition ON, engine OFF.
- Measure the voltage between:
(+) FRP Sensor Connector, Harness Side (-) VREF Ground
Is the voltage between 4.5 - 5.5 V?
Yes No GO to A4. GO to PINPOINT TEST B . - A4 CHECK THE RPM
- Ignition OFF.
- FRP Sensor connector connected.
- Access the PCM and monitor the RPM (RPM) PID.
- Crank the engine while monitoring the PID.
Is the RPM greater than 150 RPM?
Yes No GO to A5. GO to PINPOINT TEST D . - A5 CHECK THE CMP SENSOR
- Access the PCM and monitor the CMP_F (MODE) PID.
- Crank the engine while monitoring the PID.
Is a concern present?
Yes No GO to PINPOINT TEST V . GO to A7. - A6 CHECK THE VPWR VOLTAGE NOTE: An open VPWR circuit concern is indicated by a VPWR PID value greater than 15 V while the engine is running.
- Ignition ON, engine running.
- Access the PCM and monitor the VPWR (VOLT) PID.
Is the voltage less than 15 V?
Yes No GO to A7. REPAIR the open VPWR circuit.
Clear the PCM DTCs. REPEAT the self-test. - A7 CHECK THE FUEL
- Check for sufficient clean fuel. Refer to DIAGNOSTIC PROCEDURES and carry out the Sufficient Clean Fuel Test.
Is a concern present?
Yes No REPAIR as necessary.
Clear the PCM DTCs. REPEAT the self-test.GO to A8. - A8 CHECK THE LOW PRESSURE FUEL SYSTEM NOTE: On some vehicles, the FP PID may not turn off the fuel pump. Cycle the ignition from ON to OFF to command the fuel pump OFF.
- Ignition ON, engine OFF.
- For Transit,
- Access the PCM and monitor the LP_FUEL_SW (MODE) PID.
- Access the PCM and control the FP (MODE) PID.
- Command the fuel pump ON.
- For F-650/F-750,
- Access the PCM and monitor the FLP (PRESS) PID.
- Access the PCM and control the FPL_CMD (MODE) PID.
- Command the fuel pump ON.
- For all others,
- Access the PCM and monitor the FLP (PRESS) PID.
- Access the PCM and control the FP (MODE) PID.
- Command the fuel pump ON.
Does the PID state change (Transit) or is the low pressure fuel system pressure greater than 379 kPa (55 psi) (all others)?
Yes No GO to A9. GO to PINPOINT TEST MA . - A9 CHECK THE FUEL PRESSURE
- For Transit,
- Access the PCM and monitor the FRP_A (PRESS) PID.
- Crank the engine while monitoring the PID.
- For all others,
- Access the PCM and monitor the FRP (PRESS) PID.
- Crank the engine while monitoring the PID.
Is the pressure greater than 14000 kPa (2030.53 psi)?
Yes No GO to A10. GO to PINPOINT TEST M . - A10 CARRY OUT A RELATIVE COMPRESSION TEST
- Carry out the Relative Compression test on the scan tool.
Is a concern present?
Yes No REFER to the appropriate Engine System article, Diagnosis and Testing, Engine to DIAGNOSE a base engine concern. RETURN to SYMPTOM CHARTS for further direction.
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.