The ASD relay, short for Auto Shutdown Relay, is the electrical switch that supplies 12-volt power to the ignition coils and fuel injectors under control of the engine control module (PCM). When it’s working, the engine can start and run normally; when it fails, the vehicle may not start or can stall unexpectedly.
In Dodge and other Chrysler-family vehicles, the ASD relay acts as a safety-linked power gate for the engine’s critical systems. The PCM energizes the relay during crank and run, and it can disable the relay to shut down fuel and ignition if faults are detected. Because the ASD relay controls both ignition and fuel delivery, a faulty unit is a common cause of no-start or intermittent running problems, though other components can produce similar symptoms.
How the ASD Relay Works in a Dodge Engine
The ASD relay is a standard 12-volt automotive relay. Its coil is controlled by the PCM (often labeled as pins 85/86), and its contacts (pins 30/87) feed power to the ignition coils and fuel injectors. When the PCM energizes the coil, the relay closes and provides power to those circuits. If the PCM detects a dangerous fault, it may de-energize the relay, cutting fuel and ignition to protect the engine.
Key points about its role
Because it powers both the ignition and fuel delivery systems, an ASD relay failure can cause a no-start or immediate shutdown after starting. Symptoms can resemble problems with sensors, wiring, or the fuel pump, which is why testing the relay is a common diagnostic step.
Common Symptoms of a Failing ASD Relay
Below is a snapshot of typical signs that can indicate an ASD relay problem in Dodge vehicles. These signs are often reported by owners across different models and years.
- No start or crank without starting; engine does not fire up
- Engine starts briefly and stalls or dies shortly after starting
- Intermittent no-start conditions with no clear pattern
- Clicking or a lack of click from the relay when attempting to start (relay may not energize)
- Check Engine or ABS lights may appear if PCM detects an EFI fault and disables the relay
- Fuel or ignition symptoms that don’t align with typical sensor failures (e.g., no injector pulse or missing spark)
These signs can also be caused by other issues, such as faulty sensors, wiring problems, or a failing PCM. If you notice any of these symptoms, testing the ASD relay is a reasonable next step.
How to Test or Diagnose the ASD Relay
To verify whether the ASD relay is the culprit, follow a structured diagnostic approach. The steps below are common across many Dodge applications, but always consult your vehicle’s service manual for model-specific details and safety precautions.
- Inspect fuses and the relay housing for corrosion, burns, or water intrusion; fix any wiring issues before testing the relay.
- Swap the ASD relay with a known-good relay of the same type from the fuse/relay box (if a second identical relay is available) to see if the problem moves with the relay.
- Bench-test the relay: measure coil resistance across the coil terminals (often 85/86); typical values are in the tens to hundreds of ohms range depending on the relay. A very open or very low reading indicates a faulty coil.
- With the ignition off, apply 12V to the coil terminals and check continuity across the contact terminals (30 to 87). A healthy relay should switch and show continuity when energized and disconnect when de-energized.
- While cranking, verify whether the ASD relay is getting powered by the PCM (check 12V at the relay coil input). If there is no control signal, the issue may lie with the PCM or its controller circuit, not the relay itself.
- Test the loads: with the relay energized (and the engine cranking if safe), check for 12V supply to the ignition coils and fuel injectors. If there is no voltage when the PCM commands power, the relay or the wiring feeding the relay is suspect.
If these tests show the relay coil and contacts are functioning and the PCM is suggesting power delivery, the problem likely lies elsewhere (sensors, wiring, PCM, or the fuel system). If the relay fails any of these tests, replacing it is a common and often inexpensive repair.
Where to Find the ASD Relay in a Dodge
Location varies by model and year, but the ASD relay is typically housed in the under-hood fuse/relay center or power distribution center. In many Dodge cars and trucks, you’ll find a labeled relay slot marked “ASD” or a similarly abbreviated designation near other EFI-related relays. Some vans and trucks place it near the firewall or along the engine bay fuse box. Always refer to the owner’s manual or a service manual for the exact location on your vehicle.
If you’re unsure, an experienced technician or a Dodge dealership can confirm the exact location for your model year and guide you through a safe inspection or replacement.
Replacement Considerations
Replacing an ASD relay is typically straightforward and inexpensive. Consider these pointers before replacing:
- Use an exact or OEM-recommended replacement relay to ensure proper coil voltage and contact ratings.
- Disconnect the battery before removing or installing relays to avoid short circuits or sparks.
- Inspect the relay socket and wiring for corrosion or bent pins; clean or repair as needed to ensure a solid electrical connection.
- After replacement, test the starting and running condition to verify that the issue is resolved; if problems persist, recheck sensors, wiring, and the PCM.
Because the ASD relay impacts ignition and fuel systems, a faulty unit can masquerade as other ignition or EFI problems. If you’re not comfortable performing electrical diagnostics, a professional technician can perform a systematic check and confirm whether the ASD relay is the root cause.
Summary
In Dodge vehicles, the ASD relay is the Auto Shutdown Relay that provides power to the ignition coils and fuel injectors under PCM control. A healthy ASD relay enables reliable starting and running, while a failing unit can cause no-starts, stalling, or intermittent performance. Diagnostic steps typically involve visual inspection, swapping with a known-good relay, and electrical testing of the coil and contact circuits. Location varies, but it’s usually in the under-hood fuse/relay box. Replacement is usually quick and affordable, but always verify that the problem isn’t due to sensors, wiring, or the PCM itself for a lasting fix.
How do I know if my ASD relay is bad?
- Car starts but immediately stalls. One of the most common symptoms of a bad ASD relay is an engine that will start, but stall out almost immediately, or at random times.
- Engine does not crank. Another symptom of bad ASD relay is an engine that will not crank at all.
- Check Engine Light comes on.
What does ASD stand for in my fuse box?
So when I look at a wiring diagram. And I see the ASD relay. When it's being switched on by the PCM it sends an output voltage on a brown. And yellow wire and it feeds the coils.
What happens if the ECU relay is bad?
The Vehicle Won't Stay Running
The engine will stop running, and your vehicle won't move or start. Main relay problems could also lead to your engine running for a while or a very short time. Your vehicle might start normally sometimes but not start at all at other times.
What does an ASD relay do?
The automatic shutdown (ASD) relay powers the ignition coils, fuel injectors, and alternator field in many Chrysler vehicles. If this part fails, the engine can stall, fail to crank, or lag while accelerating.