Page 753 of 5267
5.ECM
Turn the ignition off.
Disconnect the Fan harness connector.
Turn the ignition on.
Measure the voltage between the sensor (K668) #2 5-volt supply (fan
speed sensor power) circuit at the fan clutch harness connector and the
fan speed sensor ground.
Is the voltage between 4.5 and 5.5 volts?
Ye s>>
Refer to the INTERMITTENT CONDITION Symptom (Diag-
nostic Procedure). (Refer to 9 - ENGINE - DIAGNOSIS
AND TESTING)
No>>
Replace the ECM.
Perform POWERTRAIN VERIFICATION TEST VER - 1
(DIESEL). (Refer to 8 - ELECTRICAL/ELECTRONIC CON-
TROL MODULES/ENGINE CONTROL MODULE - DIAG-
NOSIS AND TESTING)
Page 754 of 5267
P0643-HIGH VOLTAGE AT THE #2 SENSOR SUPPLY CIRCUIT
For a complete wiring diagramRefer to Section 8W.
Page 755 of 5267

When Monitored:
With the key on.
Set Condition:
Voltage detected on the #2 sensor supply circuit was above a calibrated value.
Possible Causes
FAN CLUTCH ASSEMBLY
(K668) 5-VOLT SHORTED TO VOLTAGE
INTERMITTENT CONDITION
ECM
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE -
DIAGNOSIS AND TESTING)
Diagnostic Test
1.FAN CLUTCH ASSEMBLY
Disconnect the Fan clutch harness connector.
NOTE: Check connectors - Clean/repair as necessary.
With the scan tool, read DTCs.
Did P0483 set?
Ye s>>
Replace the Fan clutch assembly.
Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). (Refer to 8 - ELECTRICAL/ELEC-
TRONIC CONTROL MODULES/ENGINE CONTROL MODULE - DIAGNOSIS AND TESTING)
No>>
Go To 2
2.(K668) 5-VOLT SHORTED TO VOLTAGE
Disconnect the ECM harness connectors.
Disconnect the Fan harness connector.
NOTE: Check connectors - Clean/repair as necessary.
Measure the voltage between the fan speed sensor (K668) 5-volt supply
circuit and battery negative.
Is the voltage greater than 1 volt?
Ye s>>
Repair the (K668) 5-volt supply shorted to voltage.
Perform POWERTRAIN VERIFICATION TEST VER - 1
(DIESEL). (Refer to 8 - ELECTRICAL/ELECTRONIC CON-
TROL MODULES/ENGINE CONTROL MODULE - DIAG-
NOSIS AND TESTING)
No>>
Go To 3
Page 756 of 5267
3.ECM
Turn the ignition off.
Reconnect the ECM harness connectors.
Turn the ignition on.
Measure the voltage between the (K668) 5-volt supply circuit in the sen-
sor harness connector and battery negative.
Is the voltage greater than 6 volts?
Ye s>>
Replace the ECM.
Perform POWERTRAIN VERIFICATION TEST VER - 1
(DIESEL). (Refer to 8 - ELECTRICAL/ELECTRONIC CON-
TROL MODULES/ENGINE CONTROL MODULE - DIAG-
NOSIS AND TESTING)
No>>
Refer to the INTERMITTENT CONDITION Symptom (Diag-
nostic Procedure). (Refer to 9 - ENGINE - DIAGNOSIS
AND TESTING)
Page 757 of 5267
P0646-LOW VOLTAGE DETECTED AT THE A/C CLUTCH RELAY
For a complete wiring diagramRefer to Section 8W.
Page 758 of 5267

When Monitored:
When the ignition is on.
Set Condition:
When the signal from the A/C Clutch circuit output does not match the signalfrom the A/C Clutch feedback
Possible Causes
LOW VOLTAGE SUPPLY TO THE TIPM
A/C CLUTCH CIRCUIT OPEN
A/C CLUTCH CIRCUIT SHORTED TO GROUND
TIPM
ECM
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE -
DIAGNOSIS AND TESTING)
Diagnostic Test
1.TIPM GROUND OPEN
Ignition on, engine not running.
Using a voltmeter, connect one voltmeter lead to Battery Positive and the other on TIPM ground.
Does the voltmeter show battery voltage?
Ye s>>
Go To 2
No>>
Fix or replace the open circuit in the Battery Return Circuit
Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). (Refer to 8 - ELECTRICAL/ELEC-
TRONIC CONTROL MODULES/ENGINE CONTROL MODULE - DIAGNOSIS AND TESTING)
2.LOOSE CONNECTION
Disconnect the ECM and TIPM connectors.
NOTE: Check connectors - Clean/repair as necessary.
Using an Ohmmeter, measure the resistance of the A/C Clutch signal wire between the TIPM and the ECM con-
nector..
Is the resistance less than 10 Ohms?
No>>
Fix or replace the harness.
Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). (Refer to 8 - ELECTRICAL/ELEC-
TRONIC CONTROL MODULES/ENGINE CONTROL MODULE - DIAGNOSIS AND TESTING)
Ye s>>
Go To 3
3.A/C CLUTCH CIRCUIT OPEN
Turn the ignition off.
Using an Ohmmeter, measure the resistance of the A/C Clutch signal wire between the TIPM connector and battery
negative.
Is the resistance greater than 100k Ohms?
Ye s>>
Go To 4
No>>
Fix or replace the harness.
Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). (Refer to 8 - ELECTRICAL/ELEC-
TRONIC CONTROL MODULES/ENGINE CONTROL MODULE - DIAGNOSIS AND TESTING)
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4.FUSED BATTERY SUPPLY
Connect the ECM and TIPM connectors.
Ignition on, engine not running.
Using a back probing tool 6801, back probe the A/C clutch logic pin in the TIPM logic connector.
Usinga12volttestlightconnectedtobatterypositive,checkthetransmission logic circuit at the TIPM connector
while actuating the A/C clutch circuit with the Electronic Service Tool.
NOTE: The test light must illuminate brightly.
Compare the brightness to that of a direct connection to the battery.
Does the test light illuminate brightly?
Ye s>>
Go To 5
No>>
Replace the ECM.
Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). (Refer to 8 - ELECTRICAL/ELEC-
TRONIC CONTROL MODULES/ENGINE CONTROL MODULE - DIAGNOSIS AND TESTING)
5.TIPM
Using a back probing tool, back probe the A/C clutch power pin from the TIPM power connector.
Using a 12 volt test light connected to battery positive, check the transmission power circuit at the TIPM connector
while actuating the A/C clutch circuit with the Electronic Service Tool.
NOTE: The test light must illuminate brightly.
Compare the brightness to that of a direct connection to the battery.
Does the test light illuminate brightly?
Ye s>>
Te s t c o m p l e t e .
Perform Intermittent Condition test. (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING)
No>>
Replace the TIPM.
Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). (Refer to 8 - ELECTRICAL/ELEC-
TRONIC CONTROL MODULES/ENGINE CONTROL MODULE - DIAGNOSIS AND TESTING)
Page 760 of 5267
P0647-HIGH VOLTAGE DETECTED AT THE A/C CLUTCH RELAY
For a complete wiring diagramRefer to Section 8W.