If you’re driving a car built in the past two decades, there’s a good chance it has an ASD relay. This small and seemingly unremarkable component is responsible for turning the engine off disconnecting fuel and ignition systems.
In this article, we’ll explain what an ASD relay is, why cars need it, and how it works. We’ll also look at some of the symptoms of a bad ASD relay and provide some tips on how to fix it.
The most common symptom of a bad automatic shutdown relay is the car not starting. The engine will turn over, but it will not start. Other symptoms may include the car stalling and the check engine light letting up on the dashboard.
Table of Contents
What is an ASD Relay? Where is it Located?
An automatic shutdown relay, otherwise known as an ASD, is simply a 12 Volt switch that cuts off power to the major systems of a car when you turn off the ignition key. The ASD relay is located in the engine bay, usually near the battery.
When you turn off the ignition, the ASD relay disconnects power from the fuel pump, ignition coil, and power control module. This prevents the electrical power from reaching critical engine components in case of a short circuit or wiring defect.
Why Do You Need an ASD Relay?
In the past, cars didn’t have this feature, and it was up to the driver to make sure that everything was turned off. It carries several benefits to having an ASD relay in your car:
1. New Car Have an Elaborate Electrical System:
ASD is especially important in modern cars because they have so many more electrical components than older models. If even one of these components is left on when the engine is shut off or in the case of a short circuit, it can drain the battery or cause other problems. ASD ensures that everything is properly shut down so that you can be confident that your car will start up again when you need it to.
2. A Safety Feature for Engine Management System
You could say that this is a safety feature that protects the entire engine management system. Electronic engine management systems are computer-controlled system that manages the engine’s ignition, fuel injection, and emission control systems.
The electronic engine management system constantly monitors the engine’s performance and makes adjustments to ensure optimum performance and fuel efficiency. It also helps reduce emissions by controlling the fuel injected into the engine.
The electronic engine management system is made up of several components, including the engine control module (ECM), throttle position sensor (TPS), mass air flow sensor (MAF), oxygen sensor (O2), and knock sensor (KS).
Construction of an ASD Relay; Relay Terminals and Associated Components
The ASD relay is a simple electromagnetic switch activated when 12 volts are applied to the coil. The relay has two circuits; one side controls the power to the fuel pump, ignition coil, and engine control module (ECM).
The other side of the relay contains a normally closed contact that allows current to flow through even when the relay is turned off. This side of the relay is connected to the power control module (PCM) or ignition switch. The ASD relay also contains a diode that protects the coil from voltage spikes.
In a normal ASD, there are five terminals. The number and function of each terminal are as per following:
- Terminal 30: This terminal is connected to the battery and receives power through it.
- Terminal 85: It is the grounded terminal by the power control module.
- Terminal 86: This terminal is connected to the input power source, an ignition coil, or ignition switch in this particular case.
- Terminal 87: It is used to form a closed circuit that provides output supply to the components like fuel pump relay and fuel injectors.
- Terminal 87A: It is close to terminal 87 and performs a de-energizing function. When you turn off the engine, the PCM or ignition switch sends a signal to the ASD relay, which de-energizes the coil and opens the circuit by connecting this terminal.
How Does an ASD Relay Work?
The ignition switch activates ASD relays. When you turn the key to the “on” position, 12 volts are applied to the coil, creating a magnetic field. This magnetic field pulls the contacts closed, completing the circuit and allowing current to flow through.
As long as the ignition switch is in the “on” position, the ASD relay will remain activated, and power will be supplied to the fuel pump, ignition coil, and engine control module.
When you turn the key to the “off” position, the current flowing through the coil is cut off, and the contacts open, which shuts off power to the fuel pump, ignition coil, and engine control module.
Common Symptoms of a Bad ASD Relay
If the ASD relay is not working properly, it can cause several problems. Here are some common symptoms of a bad ASD relay:
- Check Engine Light
- Engine Doesn’t Crank
- The Car Starts but the Engine Stalls
- Lag in Acceleration
The following section offers an in-depth explanation for each of these symptoms.”
1. Check Engine Light:
One of the most common symptoms of a bad ASD relay is the check engine light being illuminated on the dash. This can be caused by many different things, but if the ASD relay is not working properly, it can cause the check engine light to come on.
There are a few reasons why this might happen:
- The ASD relay might be faulty and not supplying power to the engine control module (ECM). This can cause the ECM to throw a code and illuminate the check engine light.
- The ASD relay might intermittently cut off power to the fuel pump or ignition coil. This can also cause the ECM to throw a code and illuminate the check engine light.
2. Engine Doesn’t Crank:
If your car engine doesn’t crank, it means that the starter motor isn’t turning over the engine. This can be caused by a number of things, including a dead battery, a loose connection, or a problem with the starter itself. But did you know that a bad automatic shutdown (ASD) relay can also cause the engine not to crank?
If the automatic shutdown relay is bad, it can cause the engine not to crank. This is because the ASD relay provides power to the fuel pump, ignition system, and other engine control components when the key is turned to the “On” position. If the ASD relay is faulty, these systems may not receive power and therefore will not function properly.
3. The Car Starts but the Engine Stalls:
If your car starts but the engine stalls soon after, it could be a sign of a problem with the ASD relay. This is because a faulty relay will not allow the fuel pump to deliver optimum fuel levels to the engine. This can lead to an excessively lean air-fuel mixture, which can cause the engine to stall. So, the engine would start but then stall because it is not getting enough fuel.
Another reason could be that the relay is not allowing enough electrical current to reach the ignition coils. This would cause the engine to start but stall because the spark plugs are not firing correctly.
This can be frustrating, especially in cars with electronic fuel injection systems. Because their entire fuel injection system is dependent upon automatic shutdown relays, a problem with the relay can cause serious starting and stalling issues.
4. Lag in Acceleration:
If you notice that your car is lagging in acceleration, it could be a sign of a problem with the automatic shutdown relay. There are a few reasons why a bad automatic shutdown relay can cause lag in acceleration. First, if the ASD relay is faulty, it can cause the engine to stall when idling or at low speeds. This can make it difficult to accelerate from a stop.
Additionally, a faulty ASD relay may cause the engine to run rough, leading to reduced acceleration. Fuel delivery problems and ignition delays can also cause reduced acceleration, both of which can be caused by a bad ASD relay.
What Causes an ASD Relay to go Bad?
There are a few different things that can cause an ASD relay to go bad. Here are some of the most common causes:
1. Battery Power Surge:
One of the most common causes of a bad ASD relay is a power surge from the battery. This can happen if the battery is overcharged or an electrical problem in the charging system. This can also happen if the car is jump-started with a battery that has a higher voltage than the car’s battery.
Another potential reason for battery power surge is if the car’s alternator fails and the battery is not being charged. The electrical system might try to draw power from a dead battery which can amplify the current and cause a power surge.
If this happens, the power surge in your car’s electrical system might kill some of the components, including an automatic shutdown relay. So, if you have a battery power surge, it’s best to take your car to a mechanic and have them check it out.
2. Malfunctioning Powertrain Control Module:
Another common cause of a bad ASD relay is a malfunctioning powertrain control module (PCM). The PCM is the computer that controls the engine, and it sends signals to the ASD relay to turn on and off. If the PCM is not functioning properly, it might send faulty signals to the ASD relay. This can cause the ASD relay to stay on when it should be off, or vice versa.
If the ASD relay is intermittently staying off, it will cause the engine to stall. If the ASD relay constantly stays on, it will prevent the engine from starting. Either way, a malfunctioning PCM can cause serious problems with your car’s engine.
3. Rust and Corrosion:
Over time, rust and corrosion can damage the ASD relay. This is because the ASD relay is located in the engine bay, where it is exposed to all of the elements. Rust and corrosion can cause the electrical contacts in the ASD relay to become damaged.
When this happens, it can prevent the ASD relay from making a good connection, which can cause the engine to stall. If the corrosion is bad enough, it can completely destroy the ASD relay.
4. Bad Wiring:
Bad wiring is another common cause of a bad ASD relay. If the wires that connect the ASD relay to the battery or the PCM are damaged, it can cause problems with the relay. If the wiring is damaged, it may not be able to provide adequate power to the relay, causing it to work less efficiently or even fail altogether.
Also, damage to the wiring can cause electrical shorts that can trip the relay, causing it to shut down unexpectedly. Most importantly, if the wiring is frayed or otherwise damaged, it can create excessive heat that can damage the relay itself.
How to Test a Bad ASD Relay?
In this section of the article, we’ll show you how to test a bad ASD relay in your car.
- A test light or multimeter
- Jumper Wires
1. Park Your Car:
Park your car on level ground and set the parking brake. Turn off all accessories and the engine. Open the hood and prop it up.
2. Locate the ASD Relay:
Locate the ASD relay. It is usually mounted on the fender well or inner fender near the battery. The relay will have four terminals labeled 30, 87, 87a, and 89. It looks just like your normal fuel pump relay.
3. Remove the ASD Relay:
Remove the ASD carefully from its socket. Some relays have a locking tab that must be depressed before removing the relay.
4. Testing the Terminals:
Terminals 30 and 87A
Set multimeter to the continuity setting. Check for continuity between terminal 30 and terminal 87A. There should be continuity. If there is no continuity, the relay is bad and needs to be replaced.
Terminals 85 and 86
Now, set your multimeter to the ohms setting X1. Connect the multimeter between 85 and 86. The relay is good if the multimeter reads between 70 and 80 ohms. If it reads infinity or OL, the relay is bad and needs to be replaced.
Terminals 30 and 87
Now, it is time to test terminals 87 and 30. One of these is the de-energized terminal, so if you connect these two terminals and there is continuity, the relay is bad. If there is no continuity, the connection is good.
5. Final Continuity Test:
This one is probably the most important test. This is the test that will show if the relay is actually working or not.
- Connect terminal 85 to the negative side of the 12-volt power supply with the help of a jumper wire.
- Connect terminal 86 to the positive side of the 12-volt power supply using another jumper wire.
- This should activate the relay.
- Now, using your multimeter in the continuity setting, check for continuity between terminals 30 and 87.
- There should be continuity. If there is no continuity, the relay is bad and needs to be replaced.
As you can see, testing a bad ASD relay is not that difficult. All you need is a test light or multimeter and some jumper wires. With these tests, you can easily determine if the relay is bad or not.
Replacement Cost for an ASD Relay
If you need to replace your ASD relay, the cost will vary depending on the make and model of your car. For most cars, the ASD relay is a fairly inexpensive part you can find at any auto parts store. The average cost of an ASD relay is between $80 and $110. However, if you have a luxury car or a car with a lot of electronic features, the relay can be quite expensive. For example, if you have a BMW, the ASD relay can cost upwards of $300.
Moreover, the labor cost for this procedure isn’t that high either. It is a simple swap and shouldn’t take more than 15-30 to replace the relay. Therefore, the total cost of this repair should be between $10 and $20.
Bad ASD relays are not that uncommon. In most cases, they are caused by electrical shorts or damaged wiring. If you suspect your ASD relay is bad, the best thing to do is test it with a multimeter or test light. If the relay is indeed bad, it needs to be replaced as soon as possible.
The good news is that ASD relays are relatively inexpensive and easy to replace. With a little time and effort, you can do it yourself. Just make sure to follow the testing procedures carefully and always use caution when working with electrical components.
Frequently Asked Questions
Do all cars have an ASD relay?
No, not all cars have an ASD relay. Many older vehicles do not have this feature, and some newer vehicles may have a different type of system that performs the same function. If your car does have an ASD relay, it is usually located in the engine bay near the battery. Consult your vehicle owner’s manual or a qualified mechanic if you are unsure about its location.
Is it safe to bypass ASD relay?
Yes, normally, it is safe to bypass an automatic shutdown (ASD) relay. But it is not recommended. You should only do this if you are stranded somewhere far from a workshop. The ASD relay is designed to prevent engine damage in the event of a fire or fuel leak. If you bypass the ASD relay, you are bypassing this protection.
So, if there is a fire or fuel leak, it could seriously damage your engine. Additionally, bypassing an ASD relay can also void your vehicle’s warranty. Therefore, it is important to consult with a qualified mechanic before bypassing an ASD relay.
Which cars face automatic shutdown relay failure the most?
Jeep Grand Cherokees from the years 1993-1998 are known for having ASD relay issues. Many owners of these vehicles have reported problems with their ASD relay. Additionally, BMWs and Mercedes-Benz cars are also prone to ASD relay failures. If you own one of these vehicles, it is important to be aware of this issue and to have your ASD relay regularly checked by a qualified mechanic.
What does ASD stand for?
ASD stands for Automatic Shutdown. It is a safety feature that is found in many modern cars.
What activates the ASD Relay?
The ignition switch activates the ASD relay. When you turn on the ignition, the current from the battery flows through the ASD relay and closes the circuit. This allows current to flow to the engine control module (ECM) and other systems needed for the engine to start.
What are some other relays present in a car?
There are several common relays present in a car. The most common are the starter relay, the headlight relay, and the horn relay. These relays provide power to the respective components. Other less common relays include the fuel pump relay output, oxygen sensor heater relay, and the air conditioning compressor relay. These relays provide power to the fuel pump and the air conditioning compressor.