Code
P1388
JEEP
P — Powertrain
Auto Shutdown (ASD) Relay Control Circuit Open Or Shorted
AI status
Completed
Completed
100%
Causes
- Blown or poor fuse related to ASD circuit
- Failed ASD relay
- Open wiring (broken conductor) in relay control circuit
- Short to ground or short to battery/voltage in the relay control wire
- Corroded/loose connector at ASD relay or PCM
- Aftermarket accessory wiring interfering with circuit
Symptoms
- No-start (cranks but no spark/fuel) or intermittent no-start
- Engine stalls or dies shortly after starting
- Check Engine Light (MIL) illuminated with P1388 stored
- Fuel pump does not prime when key is turned ON
- Relays may not click when cranking
What to check
- Scan for P1388 and any related codes; record freeze-frame and freeze conditions
- Visual inspection of ASD relay, fuse(s), relay socket and wiring for damage/corrosion
- Verify battery voltage is within normal range (typically 12.2–12.8 V at key-off; ~13.5–14.7 V when running)
- Listen for ASD relay click when key is turned ON or during crank; swap with known-good identical relay if available
- Backprobe ASD relay socket to verify presence of fused battery feed and PCM control signal while cranking
Signal parameters
- Battery feed to ASD relay: battery voltage (~12 V with key ON, ~>11 V while cranking)
- PCM control output to ASD relay coil: expected to switch (usually ground side) — near 0 V when activated, open/high when deactivated
- Coil resistance (ASD relay): typically tens to a few hundred ohms (varies by relay) — expect continuity (not open) when measured across coil terminals
- Current draw when relay coil energized: typically a few hundred milliamps (varies by relay)
- If PCM grounds control pin during crank/start, backprobe should show ~0 V on that pin when activated
Diagnostic algorithm
- Record freeze-frame data and note operating conditions when code set (key ON, cranking, driving).
- Verify battery voltage and condition. Low battery can cause false readings.
- Visually inspect ASD relay, fuse(s) (ASD, ECU, PCM power), relay socket and wiring for heat damage, corrosion, pin push-out or aftermarket splices.
- With ignition ON (engine off), listen for ASD relay click. If no click, try swapping with identical known-good relay (e.g., horn or A/C relay of same type) to verify relay function.
- Backprobe relay socket: verify constant battery feed terminal has battery voltage, ground terminal continuity, and PCM control terminal changes state when cranking/starting (expected ~0 V when PCM activates the relay).
- Measure coil resistance across relay coil terminals (bench) and compare to specification or a known-good relay. Replace relay if open/shorted or out of spec.
- If relay and fuses are good but PCM control signal is absent or stuck, trace/control wire from relay socket to PCM. Check for opens, shorts to ground or battery, and repair any damaged wiring or connectors. Perform wiggle tests while monitoring signal.
- If a short to power/ground is suspected, isolate sections of harness and use an ammeter/ohmmeter to locate the short. Disconnect loads (fuel pump, coils) as necessary to isolate circuit.
- Inspect for aftermarket device connections (alarms, stereos, engine management) that may have spliced into the ASD or power feed and remove or repair improper splices.
- If wiring and relay check good and PCM control output is still abnormal, verify PCM ground and power circuits. If all vehicle grounds/power are good and PCM output fails, consider PCM diagnosis/replacement following manufacturer procedures.
- After repair, clear codes and verify repair by performing starting/stall conditions and confirming P1388 does not return.
Likely causes
- Failed or intermittent ASD relay
- Open or corroded connector at ASD relay or harness
- Wire shorted to ground (common failure at vibration points)
- Wire shorted to battery/ignition feed (aftermarket wiring or damaged insulation)
- PCM output driver fault (less common)
Fault status
Status
P1388 — ASD Relay Control Circuit Open or Shorted. PCM detected abnormal condition in ASD relay control circuit (open, short to ground, or short to voltage). May disable fuel pump and ignition coils leading to no-start or engine shutdown.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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