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Engine Controls - Tests W/codes - Transmission: Maintenance Chevrolet Pickup K1500

Testing & Diagnostics ~783 words

CODE 58, TRANS FLUID TEMP. SENS CKT (HIGH TEMP. INDICATED)

The transmission fluid temperature sensor, located within the fluid pressure switch assembly, is a thermistor which controls the signal voltage to the PCM. The PCM applies and monitors voltage on circuit No. 1227 to the sensor. When transmission fluid is cold, sensor resistance is high; therefore, the PCM will see high signal voltage.

As the transmission fluid warms, sensor resistance and voltage will drop. At normal transmission operating temperature of 212°F (100°C), voltage will be about 1.5-2.0 volts. If Code 79 is also present, check the transmission cooling system. When Code 58 is set, transmission will use a warm value for operation, but scan tester will display the actual fluid temperature.

Note. Test numbers refer to numbers on diagnostic chart.

  1. Code 58 will set if signal voltage indicates a transmission fluid temperature greater than 309°F (154°C) for one second.
  2. This test determines if circuit No. 1227 is shorted to ground, which will result in conditions for Code 58.

CODE 59, TRANSMISSION FLUID TEMP. SENSOR CIRCUIT (LOW TEMP. INDICATED)

The transmission fluid temperature sensor, located within the fluid pressure switch assembly, is a thermistor which controls the signal voltage to the PCM. The PCM applies and monitors 5 volts to the sensor on circuit No. 1227. When transmission fluid is cold, sensor resistance is high; therefore, the PCM will see high signal voltage. As the transmission fluid warms, sensor resistance and voltage will drop. At normal transmission operating temperature of 212°F (100°C), voltage will be about 1.5-2.0 volts. When Code 59 is set, transmission will use a warm value for operation, but scan tester will display the actual fluid temperature.

Note. Test numbers refer to numbers on diagnostic chart.

  1. Code 59 will set if signal voltage indicates a transmission fluid temperature less than -27°F (-33°C) for one second.
  2. This test simulates Code 58. If PCM recognizes the low signal voltage (high temperature) and scan tester reads 309°F (154°C) or greater, the PCM and wiring are okay.
  3. This test determines if circuit No. 1227 is open. There should be 5 volts present at the sensor connector if measuring with a DVOM.

CODE 79, TRANSMISSION FLUID OVERTEMP

The transmission fluid temperature sensor, located within the fluid pressure switch assembly, is a thermistor which controls the signal voltage to the PCM. The PCM applies and monitors voltage on circuit No. 1227 to the sensor. When transmission fluid is cold, sensor resistance is high; therefore, the PCM will see high signal voltage.

As the transmission fluid warms, sensor resistance and voltage will drop. At normal transmission operating temperature of 212°F (100°C), voltage will be about 1.5-2.0 volts. If fluid temperature becomes greater than 304°F (150°C) but less than 309°F (154°C) for 15 minutes, Code 79 will set. If fluid temperature becomes greater than 309°F (154°C), Code 58 will also set.

Note. Test numbers refer to numbers on diagnostic chart.

  1. Code 58 will set if signal voltage indicates a transmission fluid temperature greater than 309°F (154°C). 2) This test simulates a Code 59.

The transmission fluid temperature sensor is a thermistor which controls the signal voltage to the PCM/TCM. The PCM/TCM applies and monitors voltage on circuit No. 1227 to the sensor. When transmission fluid is cold, sensor resistance is high; therefore, the PCM/TCM will see high signal voltage. As the transmission fluid warms up, sensor resistance and voltage will drop. At normal transmission operating temperature of 212°F (100°C), voltage will be about 1.5-2.0 volts.

Note. Test numbers refer to numbers on diagnostic chart.

  1. Code 58 will set if signal voltage indicates a transmission fluid temperature greater than 305°F (151°C) for one second.
  2. This test determines if circuit No. 1227 is shorted to ground, which will result in conditions for Code 58.

The transmission fluid temperature sensor is a thermistor which controls the signal voltage to PCM/TCM. The PCM/TCM applies and monitors 5 volts to the sensor on circuit No. 1227. When transmission fluid is cold, sensor resistance is high; therefore, the PCM/TCM will see high signal voltage. As transmission fluid temperature warms up, sensor resistance and voltage drop. At normal transmission operating temperature of 212°F (100°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 -34°F (-37°C) for one second.
  2. This test simulates Code 58. If PCM/TCM recognizes low signal voltage (high temperature) and scan tester reads 305°F (151°C) or greater, PCM/TCM and wiring are okay.
  3. This test determines if circuit No. 1227 is open. There should be 5 volts present at the sensor connector if measuring with a DVOM.

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