P1816 GMC - Transmission Fluid Pressure Valve Position Switch-Park/Neutral With Drive Ratio
- Faulty Automatic Transmission Fluid Pressure (TFP) Manual Valve Position Switch
- TFP Valve Position Switch harness is open or shorted
- TFP Valve Position Switch circuit poor electrical connection
- Engine Light ON (or Service Engine Soon Warning Light)
P1816 Gmc DescriptionThe automatic Transmission Fluid Pressure (TFP) manual valve position switch consists of five pressure switches (two normally-closed and three normally-open) and a Transmission Fluid Temperature (TFT) sensor combined into one unit. The combined unit mounts on the valve body.
The Powertrain Control Module (PCM) supplies ignition voltage for each range signal. By grounding one or more of the circuits through various combinations of the pressure switches, the PCM detects which manual valve position you select. The PCM 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 RUN position, the TFP manual valve position switch indicates PARK or NEUTRAL. Disconnecting the AT inline 20-way connector removes the ground potential for the three range signals to the PCM. In this case, with the engine OFF, and the ignition switch in the RUN position, D2 will be indicated.
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