Jeep Grand Cherokee WK. Manual — part 1417
P0642-SENSOR REFERENCE VOLTAGE 1 CIRCUIT LOW (CONTINUED)
For the Transmission circuit diagram (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - NAG1 - SCHE-
MATICS AND DIAGRAMS)
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 Sup-
ply 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 - TRANSMIS-
SION/TRANSAXLE/AUTOMATIC - NAG1 - STANDARD PROCEDURE)
Diagnostic Test
1.
CHECK FOR SPEED SENSOR DTCS
With the scan tool, check for other transmission 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
21 - 478
AUTOMATIC TRANSMISSION NAG1 - ELECTRICAL DIAGNOSTICS
WK
P0642-SENSOR REFERENCE VOLTAGE 1 CIRCUIT LOW (CONTINUED)
2.
CHECK FOR (T72) SENSOR SUPPLY VOLTAGE SHORT TO GROUND
Turn the ignition off to the lock position.
Disconnect the Electrohydraulic Control Unit Assembly harness con-
nector.
Disconnect the TCM C2 harness connectors.
Measure the resistance between ground and the (T72) Sensor Supply
Voltage circuit in the TCM harness connector.
Is the resistance below 5.0 ohms?
Yes
>> Repair the (T72) Sensor Supply Voltage circuit for a short
to ground
Perform NAG1 TRANSMISSION VERIFICATION TEST -
VER 1.
No
>> Go To 3
3.
CHECK FOR A SHORT IN THE ELECTOHYDRAULIC CONTROL UNIT
Reconnect the Electrohydraulic Control Unit Assembly harness con-
nector.
Measure the resistance between ground and the (T72) Sensor Supply
Voltage 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. Refer to 21- AUTOMATIC TRANSMIS-
SION-AUTOMATIC
TRANSMISSION
NAG1/SERVICE
INFORMATION for proper service procedures.
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 proce-
dures.
Perform NAG1 TRANSMISSION VERIFICATION TEST - VER 1.
WK
AUTOMATIC TRANSMISSION NAG1 - ELECTRICAL DIAGNOSTICS
21 - 479
P0643-SENSOR REFERENCE VOLTAGE 1 CIRCUIT HIGH
21 - 480
AUTOMATIC TRANSMISSION NAG1 - ELECTRICAL DIAGNOSTICS
WK
P0643-SENSOR REFERENCE VOLTAGE 1 CIRCUIT HIGH (CONTINUED)
For the Transmission circuit diagram (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - NAG1 - SCHE-
MATICS AND DIAGRAMS)
For a complete wiring diagram Refer to Section 8W
Theory of Operation
The Sensor Supply Voltage circuit supplies a 6 volt power supply for 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 overvoltage condition exist.
•
Set Condition:
When the monitored sensor voltage is not within specified limits and rises above 7.2 volts.
Possible Causes
(T72) SENSOR SUPPLY VOLTAGE CIRCUIT SHORT TO VOLTAGE
(T72) SENSOR SUPPLY VOLTAGE CIRCUIT SHORT TO OTHER CIRCUITS
TRANSMISSION CONTROL MODULE
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 21 - TRANSMIS-
SION/TRANSAXLE/AUTOMATIC - NAG1 - STANDARD PROCEDURE)
Diagnostic Test
1.
CHECK FOR SPEED SENSOR DTCS
With the scan tool, check for other transmission DTCs.
Are there any speed sensor and/or temperature sensor DTCs present?
Yes
>> Refer to the AUTOMATIC TRANSMISSION NAG1 - ELECTRICAL DIAGNOSTICS category and perform
the appropriate symptom.
No
>> Go To 2
2.
CHECK SOLENOID SUPPLY VOLTAGE ON THE SCAN TOOL
Start the engine.
With the scan tool, check the Transmission Solenoid Supply Voltage.
Is the Transmission Solenoid Supply Voltage above 7.2 volts?
Yes
>> Go To 3
No
>> Go To 5
WK
AUTOMATIC TRANSMISSION NAG1 - ELECTRICAL DIAGNOSTICS
21 - 481
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