A fuel pump is an important component of the fuel system in your vehicle. It functions similar to the heart of a human body and pumps the fuel required for the internal combustion engine (ICE) to run.
Have you ever wondered how the vehicle performs so many functions simultaneously?
This won’t be possible without the use of various relays for their effective function that is controlled and activated by the signal from the Electronic Control Unit (ECU).
Without relays, it is impossible to precisely control the interconnected function of different parts of the engine.
The ECU controls the signals to the relays depending upon whether the components satisfy certain pre-defined conditions which are programmed in the ECU.
If you are experiencing an issue of the car not getting started due to no fuel supply to the engine, then you are not alone. This is one of the most common issues reported by people.
If your vehicle’s fuel pump relay is faulty and the fuel pump is not performing its function of supplying fuel to the engine, then probably you would be looking for how to bypass fuel pump relay.
Here in this article, we will get to know the details of how to bypass fuel pump relay, other possible reasons that need to be looked into before attempting one, and the effects of bypassing fuel pump relay.
Table Of Contents
Why Would You Bypass Fuel Pump Relay? Symptoms of Bad Fuel Pump Relay
The issues of the fuel pump relay will surface out immediately as soon as it happens. Isn’t it?
No fuel pump relay operation, so the fuel pump would not be kicking in, hence no fuel and the car would stop running or doesn’t start!
How to identify a bad fuel pump relay is the question that pops into the mind whenever you come across a faulty one.
A bad fuel pump relay has two angles to it. One is that the fuel pump relay is stuck closed and there is continuous power supply in an electric circuit.
This keeps the fuel pump running continuously with key ON or key OFF, irrespective of the key position. The issues faced will be akin to bypassing the fuel pump relay.
The second is that the fuel pump relay is burnt and the circuit is discontinued and the fuel pump would never come alive unless the fuel pump relay is replaced with a new one.
It is the latter problem which people often face and get annoyed while looking for a solution.
Below are the symptoms that get manifested into your car when you are going through a bad fuel pump relay.
Engine hard starting
This is quite obvious that if the fuel pump relay has gone bad and there is no power supply to the fuel pump, then the engine won’t start as it doesn’t receive the fuel required for its operation
Engine stalls while driving
The fuel pump relay is one of the components of the engine that functions endlessly, but owing to its durability life it gets charred over a period of operation and the vehicle would die all of a sudden.
No noise from fuel pump
As discussed earlier, when the ECU grounds the fuel pump relay, the fuel pump starts priming for 3 seconds. In the case of a faulty fuel pump relay, no fuel pump priming, so you won’t hear a fuel pump priming sound from the underneath of the rear seat.
Fuel pump constantly priming
If the fuel pump relay is stuck closed, it will never give rest to the fuel pump unless it dies out. So the fuel pump would constantly prime and drain your battery till it discharges fully. So the next time, when you try to start the vehicle, it won’t pick up.
Check Engine Light (CEL)
The ECU keeps on checking the fuel pressure through fuel pressure sensors in the fuel system.
But in the event of a faulty fuel pump relay, there will be no fuel pressure in the supply line and this would make the ECU glow the CEL light on the dash.
The CEL will glow on the dash for a variety of malfunctions related to engine components so check the error codes properly before concluding on this.
How to Bypass Fuel Pump Relay?
Before we proceed to discuss how to bypass fuel pump relay, it is a prerequisite to understand how does the fuel pump relay works and what are the parts involved in it.
The fuel pump relay even though looks like a simple part but serves the major function of connecting the power source to the fuel pump whenever needed.
How does fuel pump relay work?
Usually, the fuel pump relay has a coil arrangement (85 & 86) and a contact switch (87 & 30). The current passes through the primary coil circuit, when the earthing ground is made available to the fuel pump relay electrical connections.
When the current passes through the coils, it creates a magnetic field that makes the adjacent contact switch secondary circuit arrangement close the electrical circuit that leads to the fuel pump and the pump starts running due to circuit continuity.
As soon as the ignition key is switched to ON position, the ECU supplies current to the fuel pump by grounding the fuel pump relay, so the fuel pump runs.
If the grounding signal is switched OFF by the ECU, then there will be no electric supply to the coils of the fuel pump relay.
This would mean deactivation of the coil resulting in a discontinuity in the adjacent electrical circuit and hence the fuel pump stops running.
Generally, when the car key is turned to ignition ON mode, the ECU grounds the fuel pump relay for 3 seconds to allow priming of the in-tank electric fuel pump and then deactivates it to stop the fuel pump till it gets crank sensor input.
This ensures that the fuel supply line at the fuel pump outlet is always kept under pressure to keep the injectors ready for fuel injection before cranking the engine.
When the key is further turned to START mode, the engine starts cranking and the crank sensor signals the ECU that the engine has started running so don’t stop grounding the fuel pump relay.
Hence the fuel pump relay is continuously kept grounded, so would the fuel pump operation.
In some vehicles, during the start cycle, the fuel pump relay overrides the oil pressure switch to run the fuel pump.
But once the engine starts running, the fuel pump relay turns off and the current for the fuel pump is supplied via the oil pressure sending unit which acts as a backup if the fuel pump relay fails to work.
The fuel pump relay generally has 4 pins (3 or 5 pins is also not uncommon). Out of these 4 pins, 2 pins belong to coil arrangement or control side (85 and 86) and the other 2 pins represents contact switch or load side (87 and 30)
It is through pin 85, the ECU grounds the fuel pump relay to pass current through the coil to create the magnetic field.
Pin 86 acts as input voltage supply to the fuel pump relay coil but unless the ground is available the current will not pass through the coil.
The load side pin 30 is hot-wired to the constant battery voltage and pin 87 is connected to the fuel pump terminals.
But unless the coil receives power, the contact switch won’t get activated and electrical circuit continuity won’t be established. Hence there won’t be a hot wire battery supply to the fuel pump for its running.
The pin names are typically printed on the fuel pump relay cover and the nomenclature may vary from one vehicle manufacturer to another. Hence it is advised to refer the owner’s manual, but they are often easy to follow.
In some vehicles the pin names 85, 86, 87 and 30 are renamed as pins 1, 2, 3 and 5 respectively. So here the pins 1 and 2 forms the part of coil arrangement (control side), pins 3 and 5 represents contact switch (load side).
Bypassing the fuel pump relay means, you are hot wiring directly the fuel pump to the battery voltage. This indicates, irrespective of car key position (ON/START) or even regardless of whether the car is ON or OFF, the fuel pump will run continuously and discharge fuel to the engine.
We have discussed enough on fuel pump relay now it is time to understand how to jump fuel pump relay if you are thinking of doing it.
Steps to bypass fuel pump relay
The below procedure would explain how to bypass fuel pump relay.
- First, unplug the fuel pump relay which is located under the vehicle hood inside the TIPM plastic box (sometimes called a power distribution center or relay box).
- Usually, the fuel pump relay pins are seated inside the terminals that are connected to the concerned parts at the other end.
- Use a small diameter copper wire 4 to 5 inch length to connect the terminals. Needless to say, strip the protective insulation at the ends of copper wire approximately 1/2 inch size before connecting the terminals in the relay center.
- For bypassing the fuel pump relay using a single wire, connect the terminals corresponding to contact switch pins viz. 87 and 30. (Pins 3 and 5 in case of some vehicles fuel pump relay).
- As soon as you connect the terminals with the jumper wire, you would be able to hear fuel pump priming or buzzing sound coming from the underneath of vehicle.
- In the auto market, you may come across jumper cable with two pins at each end to bypass the fuel pump relay. This also can be used.
- By doing this you would bypass the signals from the ECU to the fuel pump relay to activate the contact switch.
Once it is done, henceforth, irrespective of the ECU signal, the fuel pump will constantly receive the battery voltage and run continuously.
The fuel pump relay grounding by ECU is no more a pre-requisite condition for fuel pump running.
So when the vehicle is not getting started or it suddenly stalls while driving, it is worthwhile to confirm for a faulty fuel pump relay.
Is It Safe to Bypass Fuel Pump Relay?
Can you run a fuel pump without a relay? Yes, you can run the pump.
Can I wire my fuel pump straight to battery? Yes, it can be done but all of these shortcuts are ok as a short-term measure as it would cost at a later stage.
The above questions are the one that people frequently ask to confirm whether is it safe to bypass fuel pump relay? You would get your query answered after going through the below points.
If your vehicle stalls abruptly while driving and the root cause happens to be a faulty or burnt fuel pump relay, then bypassing the fuel pump relay would be the only option available to you as a temporary countermeasure to keep your wheels rolling.
But as a permanent solution, it is wise to replace the faulty fuel pump relay with a new one as early as possible. Otherwise, you would encounter the effects of bypassing the fuel pump relay as mentioned below.
Battery drains off
After bypassing the fuel pump relay, the fuel pump would keep on running until the battery drains off completely even if the car is in off condition.
This will kill your battery overnight and the next morning when you try to start your vehicle it would not start. Hence you would need to remove one of the battery terminals to shut off the fuel pump till you further use the vehicle.
But it is frustrating to do this temporary fix on daily basis and you may accidentally end up screwing some other electrical parts of your vehicle. In some cases, the battery would need to be replaced with a new one if you don’t pay attention to it.
Continuous fuel pump noise
You would be able to hear the fuel pump operating sound from the underneath of your rear seat even if your vehicle is switched off. Most people will find it annoying to listen to a buzzing sound when there is no other noise coming from the vehicle.
Deactivation of safety feature
In case of an accident, the inertia switch will switch off the fuel pump by deactivating the fuel pump relay but if the fuel pump relay is bypassed, then the fuel pump would keep on running and there will be chances of fuel spray all around the vehicle which may result into a possible fire hazard.
Reduced fuel pump life
The fuel pump usually lasts for certain hours of operation. If the fuel pump keeps on running endlessly then owing to its durability life, it will fail prematurely due to wear and tear of internal parts due to continuous operation and would need to replace the fuel pump with a new one more frequently.
Hotwire getting burnt
The reason we use relay is that the relay handles high voltage and/or amperage. Relays are designed to sustain high voltage and/or amperage whereas a regular switch handles low voltage.
Since a fuel pump would draw heavy current, you would need a relay to handle high amperages. The relay takes a low current switching circuit to activate the contacts to close it so that it would pass power to a high current load like a fuel pump.
If you jump the fuel pump relay, there are chances of the wiring harness getting burnt since the heavy ampere load would suck that circuit and increase the heat losses, and would burn it out.
Articles you may like to read “Fuel Pump Runs Continuously With Key On? (9 Causes And Solutions To Fix It!)”
Conclusion
The vehicle ECU monitors different signals and activates the fuel pump relay to supply power to the fuel pump.
In the event of sudden fuel pump relay failure, bypassing the fuel pump relay to momentarily fix the problem would be the right way to do.
Bypassing the fuel pump relay involves certain risks and effects on other vehicle components, hence it is prudent to consider replacing the fuel pump relay once the vehicle is ready to reach any auto store nearby.
Generally, the fuel pump relay ratings match with many other relays available in the TIPM relay box under the hood.
So it is advisable to try swapping the fuel relay with the same rating and confirm whether the vehicle starts or doesn’t stall while driving before you proceed to bypass fuel pump relay.
Hope the above information would have enhanced the awareness about troubleshooting or bypassing the fuel pump relay and have assisted you in fixing the vehicle-related problems.
Happy motoring!
References
https://www.bimmerforums.com/forum/showthread.php?2032422-Can-u-bypass-fuel-pump-relay
https://www.astrosafari.com/threads/can-you-bypass-a-fuel-pump-relay.2632/
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