What is a fuel rail pressure sensor? Bad symptoms and replacement cost

What is a fuel rail pressure sensor?

Direct injection diesel engines, as well as direct injection petrol engines, use pressure sensors that measure the fuel pressure in the rail. With this information, the Electronic Control Unit (ECU) adjusts the opening time of the injectors to deliver to the cylinders the optimal amount of fuel for combustion, depending on the operating mode of the combustion engine.

The fuel rail pressure sensor must measure the fuel pressure with fairly high accuracy and in a very short time. The information sent by this sensor is critical and absolutely necessary in the injection process.

Where is the fuel rail pressure sensor located?

The fuel pressure sensor is mounted on the high pressure rail for both diesel and petrol systems.

the common rail injection system with fuel rail pressure sensor 1
Diesel direct-injection system
Source: Bosch
  1. High-pressure pump
  2. Injector
  3. Common rail
  4. Fuel rail pressure sensor
  5. Fuel pressure regulator
  6. ECU
petrol direct injection system
Petrol direct-injection system
Source: Bosch

A fuel rail pressure sensor contains a sensitive element inside and an integrated electronic circuit. The pressurized fuel enters through a channel in the sensor body to the sensitive element. This converts the pressure into electrical voltage, which is amplified by the electrical circuit and sent through the electrical contacts to the Electronic Control Unit (ECU).

fuel rail pressure sensor
Fuel rail pressure sensor
  1. Channel (through which fuel enters under pressure)
  2. Body (contains the sensitive element and the electronic circuit)
  3. Electrical connector

The fuel pressure sensor is a resistive strain gauge sensor. The operation of this type of sensor is based on the piezoresistive effect: the electrical resistance of a conductor varies depending on the longitudinal mechanical deformation.

The sensitive element of the sensor contains several silicon-based semiconductor films, connected in the Wheatstone bridge. This architecture also allows the compensation of the effects of temperature on the sensor.

The fuel rail pressure sensor is an active one. It must be powered from a voltage source, usually + 5V. The electrical connector contains 3 pins: ground, supply voltage (AU), and output voltage (UV).

fuel rail pressure sensor with 6 pins
  1. Mass (GND)
  2. Output voltage
  3. Supply voltage

The signal (voltage) generated by the sensor, depending on the fuel pressure in the rail, varies between 0 and 70 mV. The electronic circuit integrated into the sensor evaluates and transforms this signal into a voltage that varies between 0.5 … 4.5 V.

The measuring range of a fuel rail pressure sensor is in the range 0 … 1800 (2000) bar. For the injection system to work properly, the measuring accuracy of the sensor is particularly important. At an average injection pressure, the deviation of the measured pressure from the actual value must not exceed ± 2%.

Depending on the type of injection system and the maximum injection pressure, the fuel pressure in the ramp can be 280 bar at idle and 1800 bar at maximum load.

The signal generated by the fuel rail pressure sensor is part of the closed injection control loop. When the gas pedal is pressed, the electronic control unit calculates the amount of fuel needed to obtain the desired engine torque. To do this, it calculates the pressure level at which the fuel in the common rail must be.

The pressure control is done through the pressure valve (regulator) on the injection pump or the rail. Depending on the signal received from the fuel pressure sensor, the ECU controls the pressure valve (regulator) to obtain the required pressure in the rail.

Technical characteristics of the fuel rail pressure sensor

  • Measuring range [bar] -> 0… 1800
  • Fillet -> M 18 x 1.5
  • Supply voltage [V] -> 5 ± 0.25
  • Temperature range [° C] -> – 40 … + 130
  • Response time [ms] -> 2

Symptoms of a bad fuel rail pressure sensor

In the event of a failure of the fuel rail pressure sensor, the engine will run in failure mode as it will not have information regarding the value of the rail pressure. In this case the ECU will control the pressure from the rail to the open loop.

The fuel pressure sensor is a weak link in the fuel system and many complain that they have had problems with it. It can give up due to high temperatures.

Many are wondering if they need to change the high-pressure rail along with the sensor. The answer is no. Only the sensor is changed and the repair takes less than 15 minutes.

The engine does not start or has a difficult start

The first symptoms in the event of a difficult engine start are possibly caused by a defective fuel rail pressure sensor. If the engine starts hard the first few times it will get pretty fast in not starting at all

Fuel consumption is increasing

Because this sensor is defective, then the ECU no longer knows how much fuel to deliver to the rail, resulting in the administration of a larger amount of fuel or an insufficient amount.

Check engine light (MIL) is on

Because the failure of this sensor affects the car’s engine in one way or another, the Check engine will light up to signal that a fault is present.

OBD 2 codes for a bad fuel rail pressure sensor are P0190 – P0194. So an OBD2 tester is needed to find out exactly if this sensor is the problem in this case.

Weak acceleration power

If you feel that your car is not accelerating as usual, then this sensor may be to blame. If the fuel pressure sensor is defective, then the Electoronic Control Unit can no longer properly transmit the signals to the fuel system due to erroneous information transmitted by the defective sensor.

Engine stalling

Engine stalling can happen especially when driving but also idling, this is a sign that the fuel rail pressure sensor is defective.

You feel like you’ve lost a lot of engine power.

Fuel rail pressure sensor cost of replacement

The cost of replacement will always depend on the make and model of the car. On average, the total cost of including a fuel rail pressure sensor varies between $ 200 and $ 400. The price of the sensor is between $ 50 and $ 120, depending on the car you have, and the cost of labor is around the amount of $ 150 – $ 280. Prices may vary depending on where you choose to repair your car.

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