Diagnostic Aids
WARNING: This page is about a different car, the 2002 GMC Cab & Chassis Sierra and 2002 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
An open in the ignition feed circuit 1020 causes multiple DTCs to set.
A short to voltage on the TCC PWM solenoid ground circuit can set P0741 and P1870.
DTC P1860 defaults to an elevated line pressure condition which may result in TCC partial apply. This may induce idle surge and engine stall.
Inspect wiring for poor connections at PCM and transmission 20-way in-line harness connector. Check for bent, backed out, deformed or damaged terminals. Check for weak terminal tension. Check for chafed wires that could short to bare metal or other wiring. Check for wires broken inside their insulation. If diagnosing for intermittent short or open conditions, move wiring harness while observing scan tool for value changes.