1990 Nissan-Datsun Pathfinder SE, 4D Utility, AutomaticFACTORY OEM SERVICE PROCEDURE

Ecu Power Transistor Output Signal

  1. Using a logic probe or DVOM with an analog bar graph function, carefully backprobe 20-pin ECU connector terminals No. 1, 2, 3, 11, 12 and 13 while cranking engine. This tests ECU output signals for triggering the power transistor unit.
  2. If pulse signals of approximately 0.1 volt are available at each specified ECU terminal, replace power transistor unit. If pulse signals are not available at any terminals, crank engine and check for battery voltage at terminal No. 43 of ECU connector. This checks the start signal to ECU.
  3. If voltage remains at zero during cranking, repair start signal circuit and retest. If all 6 output signals from ECU to the power transistor are okay, replace power transistor.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.

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