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What Is the ASD Relay?

Chrysler and some of its partners are the only automakers that use an automatic shutdown (ASD) relay. The auto shutdown relay is energized by the PCM and provides power to the injectors, the alternator field, and the ignition coils, along with some other less consequential components.

On newer platforms, the alternator field isn’t directly powered by the ASD relay, but the relay does send power to the PCM, which controls the alternator field. Chrysler platforms have controlled the alternator field with the engine controller since the mid-1980s.

You won’t find an auto shutdown relay on GM or Ford vehicles, nor on any non-domestic makes not directly associated with Chrysler.

The ASD relay is typically located in the power distribution center (junction box) under the hood. On later models, the ASD function isn’t a stand-alone relay but is part of the Totally Integrated Power Module (TIPM).

Symptoms of a Bad Auto Shutdown Relay

Whether the ASD relay is a replaceable relay in the junction box or is part of the TIPM, if it fails, everything that depends on that relay for power will cease to operate. The vehicle won’t even start, because the fuel injectors and the coils won’t be receiving power. Even if the vehicle could start, the alternator wouldn’t charge.

Here are the most common bad ASD relay symptoms:

pile of car relays
The ASD relay is energized by the PCM and provides power to the injectors, the alternator field, and the ignition coils, along with some other less consequential components.

Vehicle Stalls After Starting

Did you start your vehicle properly, only for the engine to die shortly afterward, seemingly at random? Stalling is one of the most common symptoms of a bad ASD relay. Relays can have dirty contacts like anything else. Even if the ASD relay initially powers up the injectors, the coils, and the alternator field, the engine may die if the contacts in the relay are dropping voltage.

Note that a bad ASD relay isn’t the only possible reason for a stalling engine. Use a scan tool to make sure the relay is the part that needs replacement.

Engine Fails to Crank

In some cases involving a bad ASD relay, you might not even get to the point where your vehicle stalls after it starts. Instead, the engine might not crank at all.

The PCM controls the ASD relay coil but also monitors the ASD relay output, and so a failed ASD relay might prevent starter operation due to PCM programming. But again, if the ASD relay has failed, the vehicle won’t start anyway.

Lag While Accelerating

The engine running roughly is another possible symptom of a bad ASD relay. This can cause delays in acceleration.

If the contacts in the relay are dropping voltage (delivering enough to the coils and injectors for the engine to run but poorly), driveability issues may result, but this doesn’t happen very often.

What Does the ASD Relay Do?

The automatic shutdown relay provides 12-volt power to the ignition coils, the fuel injectors, and the alternator field. Those are the primary components fed by the ASD.

Once the engine goes offline, the PCM will use the ASD relay to cut off the power supply to the fuel and ignition systems. This is a safety measure to prevent accidents when you’re not driving your vehicle.

A fuel system that continues to run when it’s not supposed to will waste fuel and might cause a leak or spill, which can catch fire if there’s a spark from the ignition system or another electrical system.

The ASD relay’s role of regulating the power supply for the ignition and fuel systems becomes more important during a car crash. If the fuel system gets damaged and leaks fuel, there’s a chance of fire, especially if the ignition system or another electrical system sparks. Therefore, it’s important to recognize the symptoms of a bad ASD relay and replace the faulty part as soon as possible.

More About the Automatic Shutdown Relay

In Jeeps that comply with the OBD-II specifications, the ASD relay is usually an electro-mechanical 12V relay that receives instructions from the power control module (PCM). In addition to providing power to the fuel pump, fuel injectors, and ignition coils, the relay also regulates power for the electronic throttle control (ETC) actuator. If the ASD relay develops a problem, it can affect a Jeep’s ETC system and the engine management system.

image of an asd relay
The ASD relay is typically a standard ISO relay such as the one shown in the illustration. | Image Source: Richard McCuistian

Not every vehicle has an ASD relay. Many manufacturers program their vehicles’ PCM with the ability to shut down the fuel and ignition systems.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

File Under : DIY , Ignition System
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