Affiliate link disclosure – The BMW Repair Guide uses affiliate links in their site. For more information on affiliate links, please click here.
The following article gives detailed instructions on testing and diagnosing the fuel pump in a BMW E46 325i, 325xi or 325ci vehicle (Siemens DME 42.0 and 43.0). Even though we have used a 2003 325ci to perform this repair, this article can be applied to any 2000-2005 E46 325i series vehicle with minor modifications.
A BMW E46 fuel pump test is a simple procedure that will pinpoint the cause of your pump failure.
One of the more common causes of a BMW E46 3 series not starting, having difficulty starting, or running poorly is a faulty fuel pump. Unfortunately, a problem with the electrical supply to the pump can often be misdiagnosed as an issue with the pump itself. It is crucial that a BMW E46 fuel pump test is performed to identify the exact cause of the pump's failure before purchasing unneeded parts.
The BMW E46 fuel pump test procedure is very straightforward; it involves testing the fuel pump's electrical supply to make sure it is receiving power, and if it is, verifying it is producing the proper fuel pressure. If the pump is receiving power but is not running, or is running but not producing enough fuel pressure, then the pump is faulty and needs to be replaced. If the pump is not receiving power, then there is most likely a problem with either its fuse(s) or relay.
The following is a simple electrical diagram showing how power is supplied to the fuel pump. It is important to note that the fuel pump relay is "triggered" by the vehicle's DME (engine control unit); when the key in the car's ignition is turned to start the vehicle, the DME supplies a ground to the relay, allowing power from the battery to flow to the fuel pump.
Testing the pump
Testing the pump requires two steps; the first is making sure the pump is receiving power and if it is, verifying it is producing the correct fuel pressure. Testing the BMW E46 fuel pump's power supply simply requires hooking a digital multimeter or 12V test light to the fuel pump's electrical plug, turning the ignition key to the second ("start") position, then checking the voltage. Testing the fuel pressure requires attaching a gauge to the fuel rail and attempting to start the car. The good news is BMW designed the E46's fuel pump and fuel rail to be easily accessible - it only takes a few minutes to access either one of them.
Testing the fuse and relay
If you determine power is not being supplied to the pump, then you will have to check the fuse and the relay to find the culprit. Usually, one (or both) has failed and will need to be replaced. Although technically possible, it is very unlikely that the ground from the DME is causing the issue since a DME failure would shut the entire vehicle down...not just the pump.
Checking the fuel pump fuse is simple...it is located in the glove box. Checking the fuel pump relay is unfortunately a little more time-consuming. The fuel pump relay is located in the control module rack, behind the glove box. The glove box will have to be removed and the control module rack lowered from the dashboard to gain proper access to the relay...there just isn't any shortcut method to doing this. Once the relay is removed, you can use a 12V test light or multimeter to verify that it is receiving power. Finally, you will need to "jump" the relay with a piece of wire to confirm the relay is bad.
All of this may sound complex, but it is actually very straightforward. We give you detailed step-by-step instructions below on how to perform the BMW E46 fuel pump test outlined above. If you determine that your fuel pump has failed after this test, please see our article BMW E46 Fuel Pump Replacement for detailed instructions on performing the repair.
E46 3 Series - All Models
View the detailed parts diagram for this repair.
Includes detailed part diagrams, part numbers and links to purchase all of the required components needed to complete this repair.
Before starting this repair, you must have the following required parts.
All BMW E46 models
A failing fuel pump has many potential symptoms, including: hard starting cold or after a heat soak, an illuminated check engine light, engine misfire under load or when cold, stalling, or a no-start.
All BMW E46 models
Gasket between the fuel pump/sending unit assembly and retaining collar that secures the assembly to the fuel tank.
All BMW E46 models
Factory "white green" relay that controls the fuel pump.
category = 328
Section 1 - Testing the Fuel Pump
As discussed above, testing the fuel pump is actually a two step process. First is making sure the pump is powering up and running and if it is, verifying it is producing the correct fuel pressure in the engine.
The BMW E46 fuel pump is located under the rear seat of the vehicle. To access it, grasp the bottom of the rear seat and pull out and up to release it from the body of the car. Use a bungee cord if necessary to safely stow it out of the work area.
Lift the sound insulation off of the top of the fuel pump and fold it backwards. You can now access the fuel pump cover.
Use a 10mm socket wrench to remove the four nuts securing the fuel pump cover. Remove the fuel pump cover and lay to the side out of the work area.
Grasp the fuel pump electrical connection and slide its locking mechanism out to release it. Disconnect the plug from the pump.
Flip the plug over and identify the blue/white wire. This is the 12V power supply to the pump.
Follow the wire into the plug and identify the terminal it is connected to. This is where you will check with a multimeter or test light to verify the pump is being supplied with power.
You can use either a multimeter or 12V test light when performing a BMW E46 fuel pump test. If you are working by yourself, we suggest using a test light...it is much easier to use than a multimeter if you don’t have a helper.
Connect the test light to a suitable ground - we use the door catch as shown below. Insert the test light into the 12v power terminal fed by the blue/white wire.
Turn the key to the second position. The test light should light up for approximately one second.
If the test light confirms there is power at the pump, proceed to section 4 to check the fuel line pressure. If the test light shows there isn’t power at the pump, the next step is to check the fuses and the relay.
Section 2 - Checking the Fuel Pump Fuses
There are two fuses feeding the fuel pump relay with power; a 15 amp fuse located in the glove box fuse block, and a 20 amp fuse located in the engine compartment E-box. Unless you are experiencing a host of other issues with your vehicle (like the car going into "limp mode"), it is doubtful the 20 amp E-box fuse is blown. But since it only takes a few minutes to check it, we include it in our BMW E46 fuel pump test.
Open the hood and use a T30 torx bit to remove the cover off of the E-box.
Identify the E-box fuse holder. Use a metal pick to pry the cover open on the fuse holder. Slide the cover back so the fuses can be accessed.
The 20 amp fuse in the third position is connected to the fuel pump relay. Inspect it to make sure it is not blown.
Reassemble the E-box.
Next, move to the glove box. The vehicle's main fuse block is located in the top of the glove box. Turn the two thumb releases on its cover to access the fuses.
The fuel pump 15 amp fuse is #54, approximately in the center of the fuse block. Pull the fuse and inspect it to see if it's blown.
If you had to replace either of the fuses because they were blown, retest the fuel pump to see if it has power. If it still does not have power at the blue/white terminal, then proceed to section 2 to test the relay.
Section 3 - Testing the Fuel Pump Relay
If neither of the fuel pump fuses are blown, or if you still do not have power at the fuel pump after replacing a blown fuse, then most likely the power issue is due to a faulty relay. The fuel pump relay is located behind the glove box in the control module rack. In order to access it so it can be properly tested, the glove box will need to be removed.
In order to access the fuel pump relay, you will need to remove the passenger side glove box. The first step is to detach the door from the side catches by removing the two plastic pins (rivets) with a flat blade screwdriver.
Remove the five phillips head screws securing the glove box housing to the dashboard.
Disconnect the three wiring connections from the back of the housing.
Next, the lower dashboard trim needs to be pulled loose. It is simply held in place with a plastic tab that slides into the plastic module mounting rack. Grab the trim and pull it out, then push it down and out of the way.
With the lower dash trim out of the way, you can now access the 8mm nut anchoring the bottom of the module rack to the firewall. Use an 8mm nut driver to remove the nut.
The module mounting rack is anchored at the top by two dashboard hooks that it snaps into.
To unsnap it from the two dashboard hooks, grasp the top of the mounting rack and push forward (towards firewall).
Pull the rack down so the fuel pump relay can be accessed.
Locate the fuel pump relay and remove it from its holder by grasping it with your fingers and pulling it straight out.
The first step in testing the relay is to verify it is getting power. The relay gets power at two of its four terminals; at terminal 8 from the E-box fuse block, and at terminal 6 from the glove box fuse block.
Start by verifying there is power at terminal 8 from the E-box fuse with a test light or multimeter. Use the door hinge bolt as a ground (see image below). You must turn the key to position 2 (“start”) position to test the power at terminal 8. Once you verify there is power, proceed to the next step. If you are not getting power at terminal 8, then you have an issue in the E-box...recheck fuse #3 to make sure it is not blown.
Next, you will need to verify there is not an issue between glove box fuse block and the relay. Confirm there is power at terminal 6 from the glove box fuse using a test light or multimeter. You do not have to turn the key to position 2...there is always power at terminal 6 whether the key is turned or not. Once you verify there is power, then proceed to the next step. If you are not getting power at terminal 6, then you have an issue in the glove box fuse block...recheck fuse #54 to make sure it is not blown.
Before proceeding with steps 14 and 15, you will need to make a test wire. Cut approximately six inches of 14 gauge wire and strip the ends. Crimp a 1/4" male "spade" disconnect to each end as shown below. You must have the 1/4" male spade disconnect on each end of the wire to properly insert it into the terminal for testing.
Next you will need to verify there is not a DME issue by confirming the fuel pump relay is properly grounded when the ignition key is turned on. The DME “triggers” the pump relay by supplying a ground to terminal 4 when the key is turned. Testing the DME ground is very simple. Start by inserting one end of your test wire into terminal 4 in the relay holder. Next, attach the ground lead of a test light to the the other end of the test wire. Insert the probe of the test light into terminal 8 from the Ebox fuse. Turn the ignition key to position two. If the test light activates, then you have the proper ground being supplied from the DME. If the test light does not activate, there may be an issue with the DME or with its wiring to the fuel pump relay.
Finally, you will need to confirm that there is not an electrical issue between the relay and the fuel pump. This is simply done by “jumping” terminal 6 (glove box fuse #54) to terminal 2 (fuel pump power supply). Insert one end of your test wire into terminal 6 and the other end into terminal 2. Use a test light or multimeter to verify there is power being supplied by the blue/white fuel pump plug wire. If there is power at the pump, then through the process of elimination you have determined that the relay is bad and is the cause of the pump not running. You can order a new relay by clicking here. If there is not power at the pump, then you have an electrical issue between the relay and the fuel pump plug. We suggest thoroughly cleaning the plug with CRC Electronics Cleaner and checking for any broken wires.
Section 4 - Fuel Line Pressure Test
If you have identified and repaired an electrical issue with the fuel pump and the vehicle is running normal, then there is no need to continue with this step. If you have power to the fuel pump, but your vehicle is still exhibiting symptoms of a failing fuel pump (difficult to start, engine stalling out, very poor performance) you will need to perform a fuel line pressure test. Performing a pressure test on the fuel system requires attaching a fuel pressure gauge (available from any auto parts store or our tool list above) to the fuel rail at the top of the engine. Fortunately, BMW made it very easy to access and test the fuel rail on the E46 3 series...it can be done in about 15 minutes. To perform a fuel line pressure test, please read our article BMW Fuel Pressure Test – Fuel Rail/Schrader Valve Method.
Part # 16-14-2-229-684 - The fuel pump in your vehicle is essential for delivering the proper amount of fuel at the correct pressure. Usually, they fail unexpectedly and at the worst possible time. Luckily, ECS Tuning carries a full line of replacement fuel pumps to get your vehicle back on the road again. This fuel pump installs easily in the place of your broken or worn pump. All wiring connections are the same to make this an easy plug and play installation. Don't take a chance on an inferior fuel pump from the local auto store that may leave you stranded again. Choose a quality unit to ensure thousands of worry free miles. This Genuine BMW unit is a factory direct replacement and is designed to fit just like factory. Pressure, gallons per hour, and size are the same to offer stock performance in your vehicle. Fits: BMW E46 M3 S54 3.2L
The Level of Difficulty displays graphically how challenging the repair is, from beginner to expert. Beginner repairs usually require very few tools, have short repair times and are simple to complete for even the most novice of mechanics. As the difficulty level rises expect the repair to demand more time, use more specialized tools, and require a better understanding of mechanics to complete the job.
The Repair Cost graphically displays approximately how expensive the repair will be to perform. The repair cost is defined as the actual money that would need to be spent to purchase required parts and special tools that would not be normally found in the home mechanics garage. Please note that these cost estimates are approximate and can fluctuate based on brand preferences and manufacturer.