P0642-SENSOR REFERENCE VOLTAGE 1 CIRCUIT LOW





For a complete wiring diagram Refer to Section 8W

Theory of Operation


The Sensor Supply Voltage circuit supplies a 6-volt power supply to the two input speed sensors. The Sensor Supply Voltage circuit is constantly monitored for correct voltage between 4.8 to 7.2 volts. If the voltage does not stay within the 4.8 to 7.2 volt range, the appropriate DTC will set.


  • When Monitored:

    Continuously with the ignition on and no undervoltage condition exist.

  • Set Condition:

    When the monitored sensor voltage is not within specified limits drops below 4.8 volts.


Possible Causes
  
SPEED SENSOR DTCS PRESENT
  
(T72) SENSOR SUPPLY VOLTAGE SHORT TO GROUND
  
INTERNAL SHORT IN THE ELECTROHYDRAULIC CONTROL UNIT ASSEMBLY
  
TRANSMISSION CONTROL MODULE
  

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - NAG1 - STANDARD PROCEDURE)



Diagnostic Test

1.CHECK FOR SPEED SENSOR DTCS



Are there any speed sensor DTCs present?

Yes
  • Refer to the AUTOMATIC TRANSMISSION NAG1 - ELECTRICAL DIAGNOSTICS category and perform the appropriate symptom.


No
  • Go To 2

2.CHECK FOR (T72) SENSOR SUPPLY VOLTAGE SHORT TO GROUND








Is the resistance below 5.0 ohms?

Yes


No
  • Go To 3

3.CHECK FOR A SHORT IN THE ELECTOHYDRAULIC CONTROL UNIT






Is the resistance below 5.0 ohms?

Yes


No
  • Using the schematics as a guide, check the Transmission Control Module (TCM) terminals for corrosion, damage, or terminal push out. Pay particular attention to all power and ground circuits. If no problems are found, replace the TCM per the Service Information. Refer to 8 - ELECTRICAL/ELECTRONIC CONTROL MODULES/TRANSMISSION CONTROL MODULE for the appropriate service procedures.
  • Perform NAG1 TRANSMISSION VERIFICATION TEST - VER 1. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - NAG1 - STANDARD PROCEDURE)