P0642-SENSOR REFERENCE VOLTAGE 1 CIRCUIT LOW
For a complete wiring diagram, refer to the Wiring Information.
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Theory of Operation
The Sensor Supply circuit supplies a 6-volt power supply to the two input speed sensors. The Sensor Supply 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.
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When Monitored:
Continuously with the ignition on and no undervoltage condition exist.
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Set Condition:
When the monitored sensor voltage is not within specified limits drops below 4.8 volts.
Possible Causes |
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| SPEED SENSOR DTCS PRESENT |
| (T72) SENSOR SUPPLY CIRCUIT SHORT TO GROUND |
| INTERNAL SHORT IN THE ELECTROHYDRAULIC CONTROL UNIT ASSEMBLY |
| TRANSMISSION CONTROL MODULE (TCM) |
Always perform the NAG1 Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 28 - DTC-Based Diagnostics/MODULE, Transmission Control (TCM) - Standard Procedure).
1. CHECK FOR SPEED SENSOR DTCS
| 1. | With the scan tool, check for other transmission DTCs. |
Are there any speed sensor DTCs present?
Yes
- (Refer to 28 - DTC-Based Diagnostics/MODULE, Transmission Control (TCM) - Diagnosis and Testing) and perform the appropriate diagnostic procedure.
No
- Go To 2
2. CHECK FOR (T72) SENSOR SUPPLY CIRCUIT SHORT TO GROUND
| 1. | Turn the ignition off to the lock position. |
| 2. | Disconnect the Electrohydraulic Control Unit Assembly harness connector. |
| 3. | Disconnect the TCM C2 harness connectors. |
| 4. | Measure the resistance between ground and the (T72) Sensor Supply circuit in the TCM harness connector. |
Is the resistance below 5.0 Ohms?
Yes
- Repair the (T72) Sensor Supply circuit for a short to ground
- Perform the TRANSMISSION VERIFICATION TEST. (Refer to 28 - DTC-Based Diagnostics/MODULE, Transmission Control (TCM) - Standard Procedure) .
No
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Go To 3
3. CHECK FOR A SHORT IN THE ELECTOHYDRAULIC CONTROL UNIT
| 1. | Reconnect the Electrohydraulic Control Unit Assembly harness connector. |
| 2. | Measure the resistance between ground and the (T72) Sensor Supply circuit in the TCM harness connector. |
Is the resistance below 5.0 Ohms?
Yes
- Repair the Electrohydraulic Control Unit Assembly for a short to ground.
- Perform the TRANSMISSION VERIFICATION TEST. (Refer to 28 - DTC-Based Diagnostics/MODULE, Transmission Control (TCM) - Standard Procedure).
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 and program the TCM in accordance with the Service Information.
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Perform the TRANSMISSION
VERIFICATION TEST. (Refer to
28 - DTC-Based Diagnostics/MODULE, Transmission Control (TCM)
- Standard
Procedure).