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Home >> Lexus >> 1997 >> SC 300 Standard >> Repair and Diagnosis >> External Pages >> Different car >> Section 11 (Cruise Control System) >> Circuit Testing >> Test 9: Back-Up Power Source Circuit
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Test 9: Back-Up Power Source Circuit

WARNING: This page is about a different car, the 1997 Lexus SC 400. However, it is still accessible from the selected car via links, so may be relevant.

This circuit provides power for diagnostic code memory in cruise control ECU, even when ignition is off.

  1. Check DOME fuse protecting back-up power source circuit. DOME fuse is located in engine compartment fuse/relay block.
  2. If fuse is blown, repair short circuit. If fuse is okay, remove cruise control ECU, but leave electrical connector(s) attached. Measure voltage between ground and terminal No. 15 of cruise control ECU connector. See Figure.
  3. If battery voltage is present, perform next procedure listed in DIAGNOSIS BY SYMPTOM  table under TROUBLE SHOOTING. If battery voltage is not present, repair circuit between battery and cruise control ECU.
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