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I've seen this condition before. 95% of the time it is caused by the gearshift lever assembly. There is a micro switch in there that has an open causing a battery draw. Do you plan to fix it or test for it yourself?
If you do, here is how you test it:
1. Monitor the voltage signal of the Dark Green (DG) wire at the brake shift interlock connector using a DVOM. This circuit should indicate low (grounded) voltage with the ignition on and the transmission in Park and should indicate over 8 volts when the ignition is on with shift lever take out of the Park position. Failure of the shift lever unit to ground the DG wire in the Park position of the transmission will generally cause the P in the PRND2L display to not illuminate in Park and the noted cluster lights will stay on when the ignition is turned off, creating a drain.2. Code P1706 suggests that the IC is detecting the DG wire is grounded when its also receiving a Vehicle Speed Sensor (VSS) input of more than 10 MPH from the Powertrain Control Module (PCM). If the DG wire shows low voltage even when the transmission shifter has been removed from Park, disconnect the shift lever connector and verify that the voltage of the DG wire increases to more than 8 volts indicating failure of the shift lever unit.3. If the voltage on the DG wire is low even when the shift lever connector is disconnected, check for the DG wire to be grounded in the wiring harness running between the cluster and the shift lever unit.
Let me know if you need more info.