Subaru Fuel Pressure Sensor Kit with NexGen Flex Fuel and Fuel Lines



315650 - COBB Fuel Pressure Sensor Kit (5-Pin)

2008-2021 Subaru WRX STI

Congratulations on your purchase of the COBB Tuning Subaru Fuel Pressure Sensor Kit! The following instructions will assist you through the installation process. Please read them BEFORE beginning the install to familiarize yourself with the steps and tools needed. If you feel you cannot properly perform this installation, we HIGHLY recommend you take the vehicle to a qualified and experienced automotive technician.



Parts List




Loctite 545

Tools Needed



  • 3/8" ratchet

  • 3/8" 12" extension

  • 3/8" 6" extension

  • 3/8" Socket Swivel

  • 3/8" 8mm socket

  • 3/8" 10mm socket

  • 3/8" 12mm socket


Hand Tools

  • Phillips head screwdriver

  • Flathead screwdriver



  • 22mm combination wrench

  • 5/8” combination wrench (16mm will also work)

These instructions are for installing with the COBB Fuel Rail/Line kit with or without the NexGen Flex Fuel kit. If you are looking for the old instructions they are here:

This kit REQUIRES a NexGen FlexFuel harness and module be installed in order to operate. Even if you aren’t running an ethanol content sensor.

Pre-Installation Steps

  1. Inspect the new components included with the COBB kit. If anything appears out of place, please contact COBB immediately and do not proceed with the installation.

  2. Park your car in a flat, level area and allow it to cool down all the way.

  3. Discharge the existing fuel pressure from the system. It’s a good idea to consult the factory manual for OEM methods. One potential route if you feel it can be done safely, is to let the car idle, and then remove the 15a fuse for the fuel pump. (Consult your owners manual or fusebox for which fuse this is) This will allow the car to run for a few moments longer and then stall. While there will still be some residual fuel in the system, it won’t be under pressure so you won’t cause AS big of a mess. Set the fuse and fusebox lid somewhere safe for the time being. Make sure to turn the car off after it stalls!


  4. With a 10mm, disconnect the vehicle's negative battery terminal first, If installing the full NexGen Flex Fuel kit at this time you’ll want to continue on and remove the positive battery terminal and remove the battery from the vehicle.


  5. With that you can loosen the two 10mm nuts on the hooks holding the battery in place, and remove the battery from the car to have more space available and access to where we’re going to make changes later.

  6. If Equipped with a top mount intercooler, you’ll want to remove it at this time to get to the fuel lines behind it.


  1. Add a small dab of the provided thread sealant (Recommended Loctite 545) on the pressures sensor.

  2. Install your sensor into the -6 AN → 1/8 NPT adapter.

  3. Tighten it down using your 22mm wrench to 7 ft-lbs. These are tapered NPT threads so the more you tighten the better it will seal, however over-tightening will damage the threads and the fittings.

Sensor Installation (Car Without NexGen FlexFuel Already)

  1. We start by using two -6AN wrenches to remove the AN fitting from the y adapter fitting.

  2. The AN fitting with the 1/8 NPT sensor installed can now get installed to the y-fitting.

  3. Once the sensor adapter is relatively tight on the y, you’re ready to install the rest of the fuel line. Install the AN line onto the adapter fitting.




Sensor Installation With NexGen FlexFuel

  1. The return line from the COBB Fuel Line Kit should have a y adapter coming from the two rails, along with a female to female AN fitting and then a barbed quick-connect fitting attached to a blue quick release hose. This can be done with the fittings in the car, the pictures are taken on the bench to ensure you can see what is going on.


  2. While not strictly necessary I like getting things out of the way so there isn’t as much tension on parts. So we start by gently pulling outwards on the blue legs of the quick connect fitting, and pushing the clip back. (Think awkwardly walking away from someone after a hug with your arms still straight out). The blue clip should still stay attached, just disconnect from the barb fitting.


  3. Using a -6 wrench, remove the female to female fitting from the y-adapter.


  4. The AN fitting with the 1/8 NPT sensor installed can now get installed to the y-fitting.


  5. Once the sensor adapter is relatively tight on the y, you’re ready to install the rest of the fuel line. If you’re in the process of installing a flex fuel kit, now is a great time to install the supplied AN fitting directly on to this assembly. The previous adapter and barbed fitting can get left out.


  6. If you aren’t installing a NexGen Flex Fuel kit at this time, you can install the two adapters that were on previously, adding them to the stack with the sensor, and then reconnecting the return line to the fuel pressure regulator.



Harness Installation

  1. Remove the air intake (COBB or otherwise) and locate your passenger’s side (USDM) TGV

  2. Unplug the factory harness from the tgv. From there a NexGen Flex Fuel Harness MUST BE INSTALLED in order for the fuel pressure sensor to work. Even if you aren’t running Flex Fuel or an ethanol content sensor the harness and module are required for it to read fuel pressure.

    TLDR: TGV Housing → NexGen Flex Fuel Kit → Fuel Pressure Kit → Engine Harness

  3. Now install the fuel pressure sensor harness on to the Flex Fuel harness. And plug the fuel pressure harness into the engine harness. They must be connected in the proper sequence or you will get engine codes.

  4. Route the three-pin connector end of the harness across the engine (away from any sources of heat) and plug it in to the fuel pressure sensor.

Finishing Up The Installation

  1. With all the fuel lines back together, it’s a good idea to wait a little bit until you’re sure all the fuel has dried in the engine bay and nothing flammable is anywhere near the battery.

  2. Once you’re satisfied it’s safe, reconnect the battery and tighten the terminals.

  3. Reinstall the fuel pump fuse (if removed)

  4. Turn on the car without starting it (Move the key to the accessory position, or press the button twice with your foot off any pedals). You should hear the fuel pump prime. After it has done so check the engine bay for any fuel leaks. If it’s all good, repeat this 2-3 more times to make sure everything is really tight.

  5. If you’re confident there are no leaks, go ahead and reinstall the rest of the components you removed from the car.



CARB Sticker Application

(Where Applicable)

  1. Apply the supplied CARB sticker in a clear, easy to find location.  Typically underhood, or on the radiator core support.



MAP Notes

Helps to figure out which map you should be on given the parts installed to your car 


Links for related parts

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