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Test 8-9Circuit Description with 4L80-E / 4L85-E Automatic TransmissionVehicles equipped with an active transfer case have a Four-Wheel Drive (4WD) low circuit consisting of a Powertrain Control Module (PCM) , an active transfer case control module, and the circuit wiring. The active transfer case control module controls the 4WD low signal circuit. When the operator selects 4WD low, the active transfer case control module grounds the low signal circuit, and the 4WD low signal voltage on the circuit changes from ignition voltage to zero volts. The PCM then compensates for transfer case gear reduction in the Automatic Transmission Output Shaft Speed (AT OSS) signal. The PCM uses the transmission OSS signal to adjust shift points, line pressure and Torque Converter Clutch (TCC) scheduling.Vehicles not equipped with an active transfer case have a 4WD low circuit consisting of a PCM, transfer case switch and the circuit wiring. The transfer case switch is used to control the 4WD low signal circuit. When the operator moves the 4WD selector lever to 4WD low, the transfer case switch closes, and the 4WD low signal circuit changes from B+ voltage to zero volts. The PCM then compensates for transfer case gear reduction in the automatic transmission output (shaft) speed sensor (AT OSS) readings. The PCM uses the transmission OSS signal in order to adjust shift points, line pressure and TCC scheduling.If the PCM detects a continuous open or short to ground in the 4WD low signal circuit, then DTC P1875 sets. DTC P1875 is a type C DTC. For California emissions vehicles DTC P1875 is a type B DTC.Conditions for Running the DTC
Conditions for Setting the DTC
Action Taken When the DTC Sets
Conditions for Clearing the MIL/DTC
Test DescriptionThe numbers below refer to the step numbers on the diagnostic table.
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