1995 Chevrolet Forward Control 4.3 Z, AutomaticFACTORY OEM SERVICE PROCEDURE

Code 59, Transmission Fluid Temperature Low - All Models: Notes

Transmission fluid temperature sensor is a thermistor which controls signal voltage to control module. Control module applies and monitors 5 volts to sensor. When transmission fluid is cold, sensor resistance is high; therefore, control module will see high signal voltage. As transmission fluid temperature warms, sensor resistance and voltage drop. At normal transmission operating temperature of 212Β°F (100Β°C), voltage will be about 1.5-2.0 volts.

NOTE: Test numbers refer to numbers on diagnostic chart.
  1. Code 59 will set if signal voltage indicates a transmission fluid temperature less than -34Β°F (-37Β°C) for one second.
  2. This test simulates Code 58. If control module recognizes low signal voltage (high temperature) and scan tester reads 305Β°F (151Β°C) or greater, control module and wiring are okay.
  3. This test determines if signal circuit is open. There should be 5 volts present at sensor connector if measuring with a DVOM.
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Stop DIY work and contact a certified mechanic immediately if any of the following apply:

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

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