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OBD Rail Sensor: P0087 explained

 

With knowledge comes the power to tell when a mechanic tries to rip us off, so  with these posts, I am hoping to provide Carnity members with some basic knowledge of a particular fault code to help them understand what caused a particular generic OBD II code to be set, and how the system(s)/component(s) that relate to the code work. https://carnity.com/topic/9801-how-to-scan-trouble-codes/

 

Definition of Generic Trouble Code P0087: "Fuel Rail/System Pressure Is Too Low"

What sets code P0087

This code is set when the PCM (Powertrain Control Module) receives a signal that the pressure in the fuel rail/system is lower than what is required for the engine to start, or to run properly. The required fuel pressure varies from vehicle to vehicle, but in all cases, the fuel pressure can vary between  pre-defined upper and lower limits. Thus, when the PCM detects that the fuel pressure does not fall within the specified range, code P0087 will be set.

Symptoms of code P0087

Typical symptoms include:

·         Illuminated CHECK ENGINE, or SERVICE ENGINE SOON warning light.

·         Stored trouble code.

·         Vehicle may not start.

·         Engine may be hard to start, with long cranking periods before it starts.

·         If the engine starts, there may be some hesitation on acceleration. Note that misfire-related codes may be present in these cases.  

·         Loss of power if the engine starts. Note that in these cases, there may be other codes present along with P0087.

Causes of code P0087

Typical causes include the following, although not all may be present on all vehicles.

·         Low fuel level in the tank.

·         Defective fuel pump/fuel pump relay.

·         Clogged, or dirty fuel filter.

·         Defective fuel pressure regulator, preventing the fuel system from achieving/maintaining the required fuel pressure.

·         Defective fuel pressure sensor.

·         Short circuits in associated wiring.

·         Open circuits in associated wiring due to damage to wiring.

·         Loss of ground in the wiring circuit.

·         Corroded electrical connectors, causing bad contacts/connections.

·      Defective OEM, or aftermarket security/anti-theft/immobilising devices that could prevent the fuel pump from starting. In these cases, there may, or may not be an illuminated CHECK ENGINE light present, or there may be other, vehicle-specific  codes present along with P0087.

Basic troubleshooting steps for code P0087

NOTE: When diagnosing code P0087, it is important to be sure that the fuel gauge is working properly. Many expensive fuel pumps, relays, and even PCM’s have been replaced when the vehicle simply has run out of fuel. Also, be sure to make sure that there are no leaks in the fuel system that could affect fuel pressure.

Typically, when a mechanic investigates code P0087, he will start by doing an inspection of the relevant circuits to eliminate damaged/corroded/short circuited wiring, which he will repair before doing anything else. The next step will then typically be to-

Step 1

Record all freeze-frame data and stored codes with a scanning tool, which is a sort of “snapshot” of what happened when the fault code was set. This is an important step since it may indicate an intermittent fault, which can sometimes be very difficult to find and repair.

Step 2

Clear the code, and test the fuel system to see if the code has returned.

Step 3

If the code is still present, the mechanic’s next step will be to check the fuel pressure at the fuel rail (using a dedicated fuel pressure gauge), which he will compare with the specified value for the vehicle. At this point, the mechanic will also check for the correct system voltage at the fuel pump. If the system voltage is not within specification, or absent, the mechanic will check/replace the fuel pump relay, or repair damaged wiring found during this stage of the procedure. In some cases, the battery may have to be replaced if it is defective.

NOTE: Low battery voltages can cause some fuel pumps not to start.

Step 4

If there is enough fuel in the tank, the system voltage is within specification, and the fuel pump is found to be working properly, the mechanic will check/replace the fuel filter and fuel pressure regulator before clearing the code, and retesting the system to see if the code has returned.

Step 5

If the code is still present, or the vehicle will still not start although the fuel pressure is within specification, the mechanic will test the fuel injector circuit to check for open, short circuited, or corroded wiring.

NOTE: In some cases, a vehicle can show all the symptoms of code P0087 a code relating to the fuel injectors/fuel injector circuit being present. However, this depends on the capabilities of the code reader (and its software) more than anything else does, since some cheap, or generic code readers / scanners often fail to extract some fault codes.

Step 6

If the injector circuit is OK, and the fuel pump is working, the mechanic will check the operation of the fuel pressure sensor. This check will involve checking the reference voltage (power supply) at the sensor, which is usually 5 volts for most applications. The check will also involve checking the sensor’s resistance using a special chart, called a pressure to Hertz chart. Note that it is almost impossible to diagnose a faulty sensor without this chart. The mechanic will replace the fuel pressure sensor if its resistance readings do not fall within specifications.

NOTE: This sensor converts fuel pressure into a signal voltage, which the PCM interprets as fuel pressure, which in turn is used to calculate fuel delivery (injector pulse width), and to adapt the ignition timing (among other parameters) to ensure that the engine operates efficiently. 

Step 7

If the fuel pressure sensor checks out OK, the mechanic will perform continuity/resistance/ ground checks on the wiring between the fuel pressure sensor and the PCM, making sure that the PCM is disconnected before doing so. Not disconnecting the PCM can damage it during continuity checks. If any faults are found, the mechanic will fix them at this point.

NOTE: If there is no problem with continuity or the ground, the PCM is likely to be defective, but PCM failures do not happen often, so the fault must be sought elsewhere before the PCM is replaced.

Step 8

At this point, the vehicle should start, so the mechanic will clear all fault codes, and test the vehicle with a scanner connected  to see if the code returns. This can happen if there is an intermittent fault in the wiring, so the mechanic may have to replace the affected wiring harness to ensure a reliable repair.

Codes related to P0087

P0088 - Fuel Rail/System Pressure - Too High.

Disclaimer

WHILE ALL INFORMATION IN THIS POST IS ACCURATE, IT IS INTENDED FOR GENERAL INFORMATIONAL PURPOSES ONLY. I DO NOT ACCEPT ANY RESPONSIBILITY FOR DAMAGES OF ANY KIND ARISING OUT OF THE USE, OR INCORRECT AND / OR  IMPROPER USE OF THIS INFORMATION. ALWAYS CHECK WITH YOUR MECHANIC OR THE MANUFACTURER / DEALER OF YOUR VEHICLE  BEFORE ATTEMPTING A REPAIR BASED ON THIS INFORMATION.





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