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Some Performance Insights... Some Diagnostics and ... Some Recommended Fixes for a 2009 Silverado,
But MAY assist in your present situation:
DTC C0321 01: Transfer Case Lock Circuit Short to Battery
DTC C0321 02: Transfer Case Lock Circuit Short to Ground
DTC C0321 04: Transfer Case Lock Circuit Open
DTC C0321 08: Transfer Case Lock Circuit Signal Invalid
The transfer case shift control module controls the transfer case lock solenoid. The transfer case lock solenoid is released by being energized. This is accomplished by grounding the lock solenoid control circuit during gears shifts, and in the AUTO 4WD mode. Locking action is applied when power or ground are taken away from the lock solenoid, the transfer case motor is prevented from moving. The system is capable of providing a 2HI, 4HI and 4LO lock-up without the need of additional vehicle power to hold the transfer case in these positions. This DTC detects an open lock solenoid coil, open motor lock control circuit, or an open battery positive voltage circuit, or a short to voltage or ground on the lock solenoid control circuit.
Circuit/System Testing:
The battery positive voltage circuit and the lock solenoid control circuit must be tested for opens, shorts to ground, shorts to voltage, and high resistance. This can also result from a electrically faulted solenoid.
With the ignition on check which DTC is set. If DTC C0321 is set with failure type byte 04 then do the following:
The transfer case lock is unable to hold during a hold test and the transfer case actuator will need to be replaced, and the motor learn procedure performed.
If this is not the case continue to the next step:
Disconnect the transfer case actuator, turn on the ignition and with a DMM check the battery positive voltage circuit for battery voltage at the transfer case actuator.
If battery voltage is not seen then repair the battery positive voltage circuit for an open or high resistance.
If the circuit checks out proceed to the next step:
Disconnect the transfer case control module connector X2 and check the circuit for an open, high resistance, short to ground, or short to voltage. If condition is found repair the circuit or inline connector 109 as necessary. If the condition is not found refer to component testing.
Sourcing:
Check HERE for a FREE Digital OEM Service Manual you can Download and then refer to for access to the Wiring and Component Circuitry Diagrams to help with your wiring isolation testing and diagnostics:
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