How To Reset And Troubleshoot The ASD Relay: A Complete Automotive Diagnostic Guide

To reset the Automatic Shutdown (ASD) relay, you must cycle the vehicle's ignition, clear any active Powertrain Control Module (PCM) trouble codes using an OBD-II scanner, and verify that the crankshaft and camshaft position sensors are sending valid timing signals. In most modern Chrysler, Dodge, and Jeep applications, the ASD relay is a software-controlled safety switch that automatically restores functionality once the electrical fault or sensor discrepancy—such as a short circuit or lost signal—is resolved and the ignition system is refreshed.

Diagnostic Prerequisites and System Requirements

The Automatic Shutdown (ASD) relay serves as the primary safety gatekeeper for your engine's fuel and ignition systems. Before attempting a manual reset or bypass, it is critical to understand that this relay does not "trip" like a residential circuit breaker; rather, the PCM (the vehicle's computer) intentionally withholds the ground signal to the relay coil when it detects a safety risk or a lack of engine rotation data. Attempting a reset without inspecting the underlying electrical architecture can lead to further component damage.

Essential Diagnostic Toolkit

• Digital Multimeter (DMM): Required for measuring DC voltage at the Power Distribution Center (PDC) terminals and checking continuity across relay pins.
• OBD-II Diagnostic Scanner: Essential for reading and clearing "P" series fault codes that prevent the PCM from energizing the relay.
• 12V Test Light: Useful for verifying the presence of battery voltage at the constant-power pin.
• Non-Conductive Contact Cleaner: For removing oxidation from the relay terminals and socket.
• Replacement Relay (ISO Micro/Mini): A known-good relay for substitution testing (usually interchangeable with the horn or A/C clutch relay).

Preliminary Benchmarks and Safety Standards

• Battery Voltage: Ensure the battery maintains a minimum of 12.6 volts. Low voltage during cranking can cause the PCM to drop the ASD relay connection.
• Fuse Integrity: Check the high-amperage fuse (typically 20A or 30A) dedicated to the ASD circuit in the under-hood fuse box.
• Estimated Duration: 30 to 45 minutes for a full diagnostic cycle.
• Safety Protocol: Always wear eye protection when working near the battery and ensure the vehicle is in Park with the emergency brake engaged.

Comprehensive Step-by-Step ASD Relay Reset and Diagnostic Workflow

If your vehicle cranks but refuses to start, the ASD relay has likely de-energized, cutting power to the ignition coils and fuel injectors. Follow these steps to diagnose the trigger and reset the system.

Step 1: Execute a Logic Reset via Power Cycling

The simplest way to reset the ASD relay logic is to perform a hard reset of the PCM’s temporary memory. This clears the "latch" that may be preventing the relay from engaging after a momentary electrical spike or sensor glitch.

1. Turn the ignition to the "Off" position and remove the key.
2. Disconnect the negative (black) battery terminal and wait for at least 10 minutes to allow the capacitors in the PCM to discharge.
3. Reconnect the battery terminal and tighten the nut to 10-12 lb-ft of torque.
4. Insert the key and turn it to the "On/Accessory" position (do not crank yet). Listen for the fuel pump prime and the faint "click" of the relay engaging.

Step 2: Clear Diagnostic Trouble Codes (DTCs)

The ASD relay is often held in an "Off" state because the PCM has stored a hard fault. Even if the physical problem is fixed, the software lock may persist until cleared.

1. Plug your OBD-II scanner into the port located under the driver-side dashboard.
2. Scan for codes such as P0685 (ASD Relay Control Circuit), P0688 (ASD Relay Sense Circuit Low), or P0335 (Crankshaft Position Sensor Circuit).
3. Document the codes for your records, then select "Clear/Erase Codes."
4. Cycle the key "Off" and then back "On." If the ASD relay was locked due to a software flag, the system should now be reset.

Step 3: Test for PCM Ground Triggers

The ASD relay requires two things to stay energized: constant 12V power and a ground signal provided by the PCM. The PCM will only provide this ground for about two seconds when the key is first turned on, and then continuously once it receives a signal from the Crankshaft Position Sensor (CKP).

1. Remove the ASD relay from the Power Distribution Center.
2. With the ignition in the "On" position, use your multimeter to check the relay socket.
3. Identify the "Trigger" pin (usually Pin 86 or 85). Have an assistant crank the engine while you check for a ground signal at this pin.

4. Warning: If no ground signal is detected during cranking, the problem is not the relay; the PCM is intentionally refusing to reset the circuit because it cannot "see" the engine turning over. This usually indicates a failed Crankshaft Position Sensor.

Step 4: Verify the Power Supply and Load Path

A reset is impossible if the relay has no power to distribute. You must verify the integrity of the high-current path.

1. Check Pin 30 in the relay socket using a multimeter. It should show constant battery voltage (12.6V+) at all times.
2. Check Pin 86. This should show 12V when the ignition key is in the "On" or "Start" position.
3. If Pin 30 lacks power, inspect the fusible link or the primary ASD fuse.

4. Pro-Tip: Use a jumper wire with an inline fuse to briefly connect Pin 30 to Pin 87. If the car starts, you have confirmed the fuel injectors and coils are functional, and the issue lies strictly within the relay or the PCM’s control circuit.

Step 5: Relay Substitution and Final Calibration

Relays can suffer from internal mechanical failure where the armature sticks or the coil windings burn out.

1. Locate a relay in the fuse box with the same part number (often the Horn or Cooling Fan relay).
2. Swap the known-good relay into the ASD slot.
3. Attempt to start the vehicle. If it starts, the original relay was defective and requires replacement.
4. If the vehicle starts and then stalls, the PCM is likely detecting a "Sense Circuit" error, meaning it sees that the relay closed but the voltage reaching the injectors is insufficient due to wiring resistance.

ASD Relay Pinout and Electrical Specifications

Understanding the standardized ISO relay pinout is essential for accurate diagnostics. Most ASD relays follow the 4-pin or 5-pin terminal logic.

Advanced Fault Isolation and Failure Remedies

In many cases, a simple reset will not suffice because the electrical environment is compromised. Here are the most common real-world failure scenarios and their technical solutions.

Scenario 1: The "Double Click" No-Start

• Root Cause: The PCM attempts to ground the relay, detects an immediate over-current condition (short to ground) in the fuel injector wiring harness, and instantly cuts the ground to protect itself.
• Actionable Fix: Inspect the wiring harness where it passes over the rear of the valve cover. Chafed wires here frequently short against the engine block. Insulate any exposed copper with high-temperature electrical tape or heat-shrink tubing and reset the codes.

Scenario 2: Intermittent Stalling on Bumpy Roads

• Root Cause: Oxidation or "terminal spread" within the Power Distribution Center (PDC) socket prevents the relay pins from making consistent contact.
• Actionable Fix: Remove the relay and use a small pick tool to gently tighten the female spade connectors inside the socket. Clean the contacts with specialized electrical contact cleaner and apply a small amount of dielectric grease to the relay pins to prevent future moisture intrusion.

Scenario 3: Relay Clicks but No Voltage at Injectors

• Root Cause: Internal pitting or carbon buildup on the relay’s contact points (Pin 30 to 87). The mechanical arm moves, but the electrical resistance is too high to pass current.
• Actionable Fix: Replace the relay with a high-quality OEM or equivalent component. Avoid "budget" relays which often lack the internal flyback diode required to protect the PCM from voltage spikes when the relay coil de-energizes.

Scenario 4: Valid Power but No PCM Ground Signal

• Root Cause: A failed Crankshaft Position Sensor (CKP) or Camshaft Position Sensor (CMP). Without these signals, the PCM assumes the engine is not rotating and shuts down the ASD circuit for safety.
• Actionable Fix: Monitor "Engine RPM" on a live-data scanner while cranking. If the RPM stays at 0, replace the Crankshaft Position Sensor. Once replaced, perform a battery-disconnect reset as outlined in Step 1.

Frequently Asked Questions

Can I bypass the ASD relay to get home?

While you can jumper Pin 30 to Pin 87 to provide manual power to the ignition system, this is only recommended for emergency diagnostics. Bypassing the relay removes the safety shut-off feature, meaning if you are in an accident, the fuel pump and injectors will continue to spray fuel even if the engine stops, creating a significant fire hazard.

Where is the ASD relay usually located?

The ASD relay is almost always located in the under-hood Power Distribution Center (PDC) or Integrated Power Module (IPM). It is typically grouped with the fuel pump relay, the starter relay, and the cooling fan relays. Consult the diagram on the underside of the fuse box cover for the exact location.

Why does my ASD relay keep blowing the fuse?

A blown ASD fuse typically indicates a direct short to ground in the components the relay powers. This includes the fuel injectors, the ignition coil packs, or the O2 sensor heater circuits. Unplug these components one by one to see which one is causing the fuse to pop.

What is the "ASD Sense" circuit?

The ASD Sense circuit is a dedicated wire that runs from the output side of the relay (Pin 87) back to the PCM. This allows the PCM to monitor if the relay actually closed. If the PCM grounds the relay but doesn't "see" voltage on the sense wire, it will throw code P0688 and potentially shut down the engine.

Professional Automotive Electrical Support

If the ASD relay continues to trip after performing these reset and diagnostic steps, your vehicle may have a compromised PCM or a deep-seated wiring harness failure. Consult a certified technician with a high-level oscilloscope to trace signal patterns and ensure your engine's electrical architecture is restored to factory specifications.