Circuit Description

WARNING: This page is about a different car, the 2002 GMC Yukon XL, 2002 GMC Sierra, 2002 Chevrolet Suburban, and 2002 Chevrolet Silverado. 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 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 Output Speed Sensor (OSS) signal. The PCM uses the OSS signal to adjust shift points, line pressure and 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 battery voltage to zero volts. The PCM then compensates for transfer case gear reduction in the OSS readings. The PCM uses the OSS signal 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. For California emissions vehicles, DTC P1875 is a type "B" DTC. For all other vehicles, DTC P1875 is a type "C" DTC.