Circuit Description
WARNING: This page does not describe the selected car, but rather 36 other vehicles, including the 2002 Pontiac Firebird, 2002 Oldsmobile Bravada, 2002 GMC Yukon XL, 2002 GMC Yukon, and 2002 GMC Sonoma. However, it is still accessible from the selected car via links, so may be relevant.
The PCM monitors difference between engine speed and transmission output speed. In "D3" range with TCC engaged, engine speed should closely match transmission output speed. In "D4" range with TCC engaged, TCC slip speed should be -20 to 60 RPM. DTC P1870 is set if PCM detects excessive TCC slip when TCC should be engaged.