Diagnostic Aids
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.
A false or incorrect OSS or ISS signal can set DTC P0730. DTC P1870 detects an incorrect gear ratio in 4th gear with TCC applied. Inspect for any improperly installed after-market equipment. Sticking or contamination of shift valves may cause intermittent incorrect gear ratios. DTC P0730 defaults to an elevated line pressure condition which may result in TCC partial apply. This may induce idle surge and engine stall.