Circuit/System Description
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The four wheel drive (4WD) low circuit consists of the engine control module (ECM), a transfer case control module and the circuit wiring. The transfer case control module controls the 4WD low signal circuit. When the operator selects 4WD low, the transfer case control module grounds the signal circuit, and the 4WD low signal voltage on the circuit changes from ignition voltage to zero volts. The ECM then compensates for transfer case gear reduction in the transmission output shaft speed (OSS) sensor signal. The ECM uses the transmission OSS sensor signal to adjust shift points, line pressure and torque converter clutch (TCC) scheduling.