Circuit Description

WARNING: This page is about a different car, the 2007 GMC Yukon XL and 2007 Chevrolet Suburban. However, it is still accessible from the selected car via links, so may be relevant.

The automatic transmission fluid pressure (TFP) manual valve position switch consists of 5 pressure switches and a transmission fluid temperature (TFT) sensor combined into 1 unit. The combined unit mounts on the valve body. The transmission control module (TCM) supplies ignition voltage for each range signal. By grounding 1 or more of these circuits through various combinations of the pressure switches, the TCM detects the manual valve position you select. The TCM compares the actual voltage combination of the switches to a TFP manual valve position switch combination table stored in memory.

The TFP manual valve position switch cannot distinguish between PARK and NEUTRAL because the monitored valve body pressures are identical. With the engine OFF and the ignition switch in the ON position, the TFP manual valve position switch indicates PARK/NEUTRAL. Disconnecting the automatic transmission (AT) inline 20-way connector removes the ground potential for the 3 range signals to the TCM. In this case, with the engine OFF, and the ignition switch in the ON position, D2 will be indicated.

When the TCM detects PARK/NEUTRAL or drive gear with a REVERSE ratio, DTC P1818 sets. DTC P1818 is a type B DTC.