Circuit Description

WARNING: This page is about a different car, the 2007 GMC Yukon XL, 2007 GMC Yukon, 2007 Chevrolet Tahoe, 2007 Chevrolet Suburban, and 2007 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.

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.

When the ECM detects a continuous open, short to ground or short to voltage in the 4WD low circuit, then DTC P2771 sets. DTC P2771 is a type B DTC.