Powertrain Diagnosis

Circuit Description
The Automatic Transmission Fluid Pressure (TFP) Manual Valve Position Switch consists of five normally-open pressure switches. The Powertrain Control Module (PCM) supplies battery voltage to each range signal. By grounding one or more of these circuits through various combinations of the pressure switches, the PCM detects what manual valve position has been selected and compares the actual voltage combination of the switches to a TFP Manual Valve Position Switch combination chart stored in memory.

The TFP Manual Valve Position Switch cannot distinguish between PARK and NEUTRAL because the monitored valve body pressures are identical in both cases. With the ignition ON and the engine OFF, D2 is indicated. When the transmission 20-way connector is disconnected, the ground potential for the three range signals to the PCM is removed, and with the ignition ON, D2 is indicated.

If the PCM detects an invalid state of the TFP Manual Valve Position Switch Circuit by deciphering the TFP Manual Valve Position Switch inputs, then DTC P1810 sets. DTC P1810 is a type B DTC.

Conditions for Running the DTC
^ System voltage is 8.0-18.0 volts.
^ The engine is running greater than 475 RPM for greater than 7 seconds.

Conditions for Setting the DTC
The PCM detects an illegal TFP Manual Valve Position Switch combination for greater than 60.0 seconds.

Action Taken When the DTC Sets
^ The PCM illuminates the Malfunction Indicator Lamp (MIL).
^ The PCM commands maximum line pressure.
^ The PCM assumes D4 for the PRNDL shift pattern.
^ The PCM freezes shift adapts.
^ The PCM stores DTC P1810 in PCM history.

Conditions for Clearing the MIL/DTC
^ For Federal and California emissions, the PCM turns OFF the MIL during the third consecutive trip in which the diagnostic test runs and passes.
^ A scan tool clears the DTC from PCM history.
^ For Federal and California emissions, the PCM clears the DTC from PCM history if the vehicle completes 40 consecutive warm-up cycles without an emission related diagnostic fault occurring.
^ For vehicles equal to or greater than 15,000 lbs GVW, the PCM clears the DTC from PCM history if the vehicle completes 40 consecutive warm-up cycles without a non-emission related diagnostic fault occurring.
^ The PCM cancels the DTC default actions when the fault no longer exists and the ignition switch is OFF long enough in order to power down the PCM.

Diagnostic Aids
^ Refer to the accompanying table for the normal range signals and the illegal combinations.
^ Inspect the wiring at the PCM, the transmission connector and all other circuit connecting points for the following conditions:
- A backed out terminal
- A damaged terminal
- Reduced terminal tension A chafed wire
- A broken wire inside the insulation
- Moisture intrusion
- Corrosion
^ When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change.
^ DTC P1810 can be falsely set during a fluid fill procedure. After refilling the fluid, cycle key down then start and run the vehicle for 20 seconds. key down and allow the PCM to power down, and then restart the vehicle.
^ DTC P1810 can be set falsely by low pump pressure or a stuck pressure regulator.
^ DTC P1810 can be set by a rolled forward clutch piston seal. It may allow the PCM to see a 2.08:1 ratio (REVERSE) when the manual valve position is indicated as D4.
^ First, diagnose and clear any engine DTCs that are present. Then inspect for any transmission DTCs that may have reset.
^ Refer to the Range Signal table.

Test Description
The numbers below refer to the step numbers on the diagnostic table.
3. This step tests the indicated range signal to the manual valve that is actually selected.
4. This step tests the voltage from the PCM to the transmission 20-way connector.