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DTC codes / GM codes / P1388

P1388 · GMAuto Shutdown ASD Relay Control Circuit Open Or Shorted

P1388 on a GM vehicle means the engine control module (ECM) has detected an open or shorted circuit in the control wire for the Auto Shutdown (ASD) relay, which is the relay that powers the fuel pump, ignition coils, and fuel injectors. The ECM commands the ASD relay on when the ignition is on and the engine is cranking or running, and it monitors the control circuit for expected voltage changes; when the voltage does not match the commanded state, it sets this code.

SystemPowertrain
Code typeGM specific
SeverityMedium
Fix difficultyIntermediate
AreaIgnition system and misfire

Symptoms you may notice

  • The engine cranks but does not start because the fuel pump and ignition are not powered.
  • The engine starts and then stalls immediately after the ASD relay drops out.
  • The service engine soon light is illuminated, often with no other noticeable symptoms.
  • Intermittent no-start or stall conditions that may be temperature or vibration related.
  • Other systems that share the ASD relay circuit, such as the fuel pump and ignition, may be inoperative.

Common causes, most likely first

  1. A failed ASD relay, where the coil is open or the contacts are burned.
  2. A blown fuse that supplies power to the ASD relay coil or contacts.
  3. Damaged wiring in the ASD relay control circuit, such as a rubbed-through wire shorting to ground or a broken wire.
  4. Corroded or loose terminals at the ASD relay socket or at the ECM connector.
  5. A faulty ECM driver for the ASD relay control circuit, though this is less common.
  6. An aftermarket alarm or remote start system improperly tied into the ASD circuit.

How to diagnose and fix it

  1. Verify the battery is fully charged and check all underhood fuses related to the ASD relay, including the relay coil fuse and the main relay power fuse.
  2. Swap the ASD relay with an identical known-good relay from the fuse box and clear the code to see if it returns.
  3. Inspect the ASD relay socket and ECM connectors for corrosion, loose pins, or pushed-out terminals.
  4. Use a wiring diagram to locate the ASD relay control wire and check for continuity from the ECM connector to the relay socket; repair any open or shorted wiring.
  5. With the ignition on, measure voltage at the ASD relay control terminal while commanding the relay on with a scan tool to confirm the ECM driver is functioning.
  6. Check for aftermarket accessories spliced into the ASD circuit and remove or repair any improper connections.
  7. Clear the code and perform a road test, including a wiggle test of the harness, to confirm the repair.

ASD relay circuit checks most technicians miss

  • A common mistake is replacing the ASD relay without checking the control circuit; the relay may be fine while a chafed wire shorts the control line to ground.
  • The ASD relay often shares power with the fuel pump and ignition, so a no-start with P1388 can be misdiagnosed as a bad fuel pump when the relay control circuit is the real fault.
  • Aftermarket alarms or remote start systems are frequently spliced into the ASD circuit and can introduce an intermittent open or short that sets this code.
  • The ECM driver for the ASD relay can fail, but before condemning the ECM, verify that the control wire is not shorted to voltage or ground, as a short can damage the driver.
  • On some GM vehicles, a weak battery or poor ground can cause the ASD relay to chatter and set P1388 without any hard wiring fault.

Can I keep driving with P1388?

If the engine starts and runs normally, you can drive the vehicle to a repair shop, but avoid long trips and be prepared for a stall. If the engine cranks but does not start, do not keep cranking; have the vehicle towed to prevent starter damage and safely diagnose the no-start condition.

Tools that help

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Guidance is general and written for GM vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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