Fixing Low Fuel Pressure Sensors: A Step-By-Step Guide

Changing a low fuel pressure sensor can be a challenging task, and it is important to first diagnose the issue correctly before attempting any repairs. A faulty fuel pressure sensor can cause various issues, such as difficulty starting the engine, weak acceleration, poor fuel mileage, and a check engine light.

Before attempting to change the sensor, it is recommended to check for other potential issues, such as a leaking or clogged fuel filter or a faulty fuel pump. If the sensor is indeed the problem, the repair process will vary depending on the vehicle's specific make and model.

For example, for a 2010 535i (E60, N54), the process involves removing the microfilter, cowl, air box, and throttle body. It is also necessary to remove the Wiring Harness Junction Box, which can be tricky. Finally, the sensor can be unplugged and replaced with a new one, being careful not to over-tighten it.

It is generally recommended to consult a professional mechanic or a reliable repair guide specific to your vehicle's make and model before attempting any repairs yourself.

Removing the microfilter and cowl

The first step in changing the low-pressure fuel sensor on an N54 engine is to remove the microfilter and cowl. This process is straightforward and only requires the removal of the driver's side. There are already several step-by-step instructions available online for this process, so you can easily find a guide to follow.

Once the microfilter and cowl are removed, you can move on to the next step of changing the low-pressure fuel sensor. This process may vary depending on your vehicle's specific make and model, but it generally involves accessing and removing the sensor, and then installing a new one.

Removing the Air Box

After removing the microfilter and cowl, the next step is to remove the air box. This process is similar to the previous one, and you can find step-by-step instructions online. Removing the air box will give you access to the throttle body, which needs to be removed next.

Removing the Throttle Body

To remove the throttle body, first, remove the torx fastener located at the opposite end of the pipe. Then, pry up on the clip holding the pipe to the throttle body with a flat-head screwdriver and pull the hose off. Remove the four 10mm fasteners holding the throttle body to the intake manifold. Torque the fasteners to 8nm when reinstalling. There is also a vacuum line leading out of the back of the throttle body; squeeze and rotate it to remove it. Finally, unplug the electrical connector and move the throttle body to the side, covering it with a rag to keep it clean.

Removing the Wiring Harness Junction Box

The wiring harness junction box can be a bit tricky to remove. It is held in place by a metal bracket, and you will need to gently pry it up and bend the plastic upward to slide the junction box over the metal catch. Be careful not to damage the surface of the intake manifold where the throttle body mounts, as this needs to remain smooth for the throttle body o-ring to seal properly.

Removing the air box

To remove the air box, first remove the intake air snorkel by unclipping the plastic clips and removing the connecting sleeve. Next, disconnect and remove the battery, taking care to remove the negative terminal first and replace it last. Now, disconnect and remove the air filter cover and the air filter element, being careful not to let the contents of the air filter fall into the intake pipe.

Depending on what you need to access, you may need to remove the intake tube. If so, disconnect and remove it, checking for any cracks and replacing if necessary.

To access the lower air filter housing, you will need to remove the front bumper. With the bumper removed, you can now access the lower air filter housing. Disconnect and remove the "resonator", which is the forward part of the lower air filter housing where the intake snorkel connects. This is held in place with two bolts and a connecting sleeve.

Now, you can remove the whole main lower section of the air filter housing.

Removing the throttle body

To remove the throttle body, you will need the following tools:

• 8mm socket (throttle cable assembly)
• 10mm socket (negative battery cable)
• 13mm socket (throttle body hold-down bolts)
• #25 Torx driver (throttle body sensors)
• 3/16” Allen wrench (new throttle body hold-down bolts)

Now, follow these steps:

Step 1: Remove the Throttle Body Hat

If you have an aftermarket air intake, this will be easy. If not, remove the flex hose.

Step 2: Disconnect the Electronic Connections

There are three electronic connections attached to the throttle body. One is at the rear, and two are on the driver's side. Push down on the tab and pull off the two on the side. For the one at the rear, lift the tab a bit to slip it off. You can also remove the vacuum line from the front of the throttle body.

Step 3: Disconnect the Throttle Cables

There are three cables attached to the throttle body. They are held on by a "C" connection. To remove them, push the little black parts at the end of the cables in the opposite direction.

Step 4: Remove the Throttle Cable Attachment Brace

There are three 8mm bolts holding the throttle cable attachment brace to the throttle body. Two bolts are in the front, and one is behind the spring on the side. Keep these bolts, as you will need them later.

Step 5: Remove the Throttle Body

Remove the four bolts on top of the throttle body. Once they are removed, lift the throttle body off the intake plenum. Cover the opening to prevent anything from falling into it.

Step 6: Remove and Install Sensors

Away from the engine, remove all the sensors and install them on the new throttle body. You will need a #25 Torx wrench for this. The idle motor is at the back, the throttle position sensor is on the driver's side, and the MAP sensor is in front.

Step 7: Prepare the Intake Plenum

Remove any gasket material from the intake plenum and put down the new gasket included with the kit. Do not use any RTV.

Step 8: Install the New Throttle Body

Place the new throttle body on the gasket and start the bolts into the plenum. Start all four bolts first, then tighten them down. Remember not to over-tighten, as the intake plenum is made of aluminum.

Step 9: Reattach the Throttle Cable Attachment Brace and Cables

Attach the cable support brace using the stock 8mm bolts you removed earlier and reattach the cables and electronic connections.

Step 10: Install the S Bolt

Thread the S bolt until the double nuts hit the throttle body. If it is not aligned, loosen the bolts and turn it until it is properly aligned, then tighten it down.

Step 11: Reinstall the Throttle Body Hat

Put back the throttle body hat and anything else you removed earlier.

Step 12: Reset the Computer

Disconnect the negative side of the battery for 10 to 20 seconds to reset the computer and allow it to relearn the settings with the new airflow rates. It should reset in about 40 miles.

Please note that it is not recommended to remove the throttle body for cleaning, especially if you have a DBW (Drive By Wire) throttle.

Removing the wiring harness junction box

To remove the wiring harness junction box, you will need the following tools:

• Adequate lighting
• Utility knife
• Small needlenose pliers (optional)
• Longish flathead screwdriver
• Very small flathead screwdriver
• Wire strippers
• Electrical tape
• Solder
• Soldering iron
• Side cutters pliers

First, you will need to remove the plastic shield that protects the bare wiring of the ECU harness. This is secured by a zip tie and clips on either side. Use side cutters to clip the zip tie, then use a small needlenose pliers near the base of the shield/bundle of wires to gently squeeze both sides of the shield until it pops off.

Next, locate and remove the purple retaining clip. You may need a small flathead screwdriver to get it started. With the clip removed, you will be able to pull out the small white wiring harnesses. Each wire is numbered, so identify the correct one before proceeding.

Now, you are ready to remove the individual pin/wire. Insert a very small screwdriver or pointed razor blade into the slot located away from the bare wire. This will depress a retaining tab on the pin, allowing you to pull the wire from the harness.

If you need to remove a wire from a junction box, start by identifying the connector you will be working with. Use a long flathead screwdriver to disconnect the clips on either side (top and bottom) of the connector. This step can be tricky, as you have to do one side at a time and they may clip themselves back in. Once the first side is unclipped, pull on the wiring harness until the other side is unclipped as well.

Now, move the retaining clip by pushing from the back or pulling from the front. You will feel two distinct clicks as the retaining clip has three possible positions: 0, 1, and 2. For small pins, we want position 1, which is partially removed.

Finally, locate and remove the pin/wire. Each wire is numbered in the wiring harness, and the retaining pins have tabs oriented down towards the center of the connector. Use a small flathead screwdriver to carefully push the tab up towards the pin, then pull the wire out.

Note: It is recommended to tap the wires instead of pulling the pins from the connectors, as this can easily damage the connectors.

Removing the old sensor and replacing with a new one

To remove the old low-pressure fuel sensor and replace it with a new one, follow these steps:

Step 1: Remove the Microfilter and Cowl

There are already several step-by-step instructions available online for removing the microfilter and cowl, so you can refer to those. Note that you only need to remove the driver's side.

Step 2: Remove the Air Box

This can be done in a similar way to the previous step, by following instructions available online.

Step 3: Remove the Throttle Body

First, remove the torx fastener located at the opposite end of the pipe. Then, pry up on the clip holding the pipe to the throttle body with a flat-head screwdriver and pull the hose off. Remove the four 10mm fasteners holding the throttle body to the intake manifold. There is also a vacuum line leading out of the back of the throttle body; squeeze and rotate to remove it. Finally, unplug the electrical connector and move the throttle body to the side and cover it with a rag. You may also want to clean it with carb cleaner.

Step 4: Remove the Wiring Harness Junction Box

To do this, you will need to create a special tool by ruining a screwdriver. Wedge the tip of the screwdriver under the plastic slot so that it is wedged between the Wiring Harness Junction Box and the metal bracket holding it in place. Gently pry up to bend the plastic upward, so you can slide the junction box over the metal catch while pulling towards you. Do this for both sides. Be careful not to damage the surface of the intake manifold.

Step 5: Disconnect the Electrical Connector from the Low-Pressure Fuel Sensor

Using a small flat-head terminal screwdriver, pry back the clip on the electrical connector and pull up to unplug it.

Step 6: Remove the Old Low-Pressure Fuel Sensor and Replace with the New One

Using a 24mm or 15/16 wrench, remove the old sensor. Be careful not to over-tighten when installing the new sensor, as this could result in stripping the threads or snapping it off. The torque spec for the sensor is 20-3 Nm.

Finally, put everything back together in the reverse order of disassembly.

Frequently asked questions