Diagnostic Trouble Code Meaning: Pressure too low in the fuel rail/system
- Check Engine Light is on
- Misfiring at higher RPMs
- Poor fuel mileage
- Fuel pump clogged, weak or the supply is restricted
- Fuel pump driver module is bad
- Fuel pressure sensor is bad
In vehicles that have a returnless fuel supply, there is a sensor used to monitor the fuel pressure and control the pump speed. A returnless fuel supply is a pump that is pulse-width modulated, which allows it to use variable rate to deliver the fuel rather than a continual stream of fuel regulated by way of a pressure regulator. This fuel supply is regulated on the rail. When low pressure is detected by the PCM or ECM, this code is displayed.
What The Tech Says
A vehicle that has a fuel pressure port can be checked using a pressure gauge. This port may be at the rail or line, and you should look for pressure within the specifications of your vehicle. Additionally, the pressure should be tested under load by putting the car in gear or accelerating it. Should you find that the pressure is below specifications, look for a problem in one of the fuel lines. It could be bent or otherwise restricted.
A fuel filter that has not been changed can also be the cause of the restriction of fuel flow. The screens get dirty, so fuel filters need to be cleaned. If you have had any damage to the gas tank, it may be pressing into the fuel pump inlet. (Read more about fuel pumps in this blog on BlueSpringsFordParts.com.)
The fuel pump driver module is operated on a pulse input signal from the ECM or PCM, and a pulse output signal that is sent to the pump. There may be a problem with the driver module, which could cause the wrong signal to be sent. You can check the module by using your wiring diagram and a DVOM. Set the DVOM to duty cycle, since that is what type of cycle the module uses, and put the negative lead on good ground, and the positive lead on the signal wire.
The duty cycle will vary in relation to the commands sent from the PCM or ECM to the fuel pump. Ford doubles the duty cycle output, which means that a 30 percent input will give you a 60 percent output to the fuel pump. Fuel pump duty cycle will deliver this result. The PCM normally monitors the voltage, and there may be an additional DTC specifically for the pump driver module.
The problem may be in the fuel pressure sensor, which can be checked by using your wiring diagram and DVOM. The PCM typically monitors the voltage, and there will be a reference for this. You may see an additional code for a problem with the ground or power wires. It may set a P0190 code if there is a problem with the sensor circuit, and a P0191 code tells you there is a problem with the sensor circuit range or performance.
There may be an incorrect reading if there is excessive resistance within the sensor or wire leads. Use your DVOM in ohms scale, and check the pressure sensor’s resistance by unplugging it and placing the negative and positive leads onto the sensor connector. Replace the sensor if the resistance is higher than specs. You can test the wiring by setting the DVOM to ohms scale and disconnecting the PCM and the sensor. Then check for excessive resistance between the wiring harness terminal ends with the negative lead on the end of the wiring harness and the positive DVOM lead on the other end of the harness.