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LS400 Theft Deterrent Ecu Power Circuit Test

  1. Turn ignition off. Check 10-amp DOME fuse in junction block No. 2. See Figure. Replace fuse if necessary. Check for a short in all circuits related to DOME fuse. Repair circuit(s) as necessary.
  2. If fuse was okay in step 1), disconnect ECU harness connectors. Theft deterrent ECU is located under left side of dash, above junction block No. 1. Using a DVOM, check for battery voltage between ECU harness connector terminals A20 and A16. See Figure. If okay, go to next step. If battery voltage is not present, go to step 5).
  3. Check DOOR circuit breaker in junction block No. 1. If circuit breaker is open, check for shorts in all circuits related to DOOR circuit breaker. Repair circuit(s) as necessary.
  4. Check actuator motors and solenoids for operation by applying battery voltage to solenoid or motor connectors for one to 2 seconds. Repair or replace as necessary.
  5. If battery voltage is not present in step 2), check for continuity between harness connector terminal A16 and body ground. Repair ground or harness as necessary.
  6. If ground circuit is okay, check and repair related wire harness between ECU connector terminal A20 and battery. If all circuits are okay, replace ECU, and retest system.
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