Circuit Description

WARNING: This page is about a different car, the 2006 GMC Yukon XL, 2006 Chevrolet Suburban, and 2006 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.

Vehicles 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 vehicle speed sensor (VSS) 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 AT OSS readings. The PCM uses the transmission VSS 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, DTC P2771 sets. DTC P2771 is a type C DTC. For California emissions vehicles DTC P2771 is a type B DTC.