Buick Century Engine Problem

Circuit Description
The automatic transmission fluid pressure (TFP) manual valve position switch consists of six pressure switches (three normally-closed and three normally-open switches). Ignition voltage is applied to each of the switches. By grounding or opening one or more of these switches with fluid pressure from the manual valve, the PCM can detect which gear range is selected. Refer to Transmission Fluid Pressure (TFP) Manual Valve Position Switch Logic.
If the PCM detects an invalid combination of inputs, LOW/HI/LOW or LOW/LOW/LOW, then DTC P1810 sets. If the PCM detects a gear range other than the one indicated, then DTC P1810 sets. DTC P1810 is a type B DTC.

Conditions for Running the DTC
The system voltage is 9 - 18 volts.

Conditions for Setting the DTC
DTC P1810 sets when at least one of the following conditions occurs:

Condition 1

The engine speed is greater than 500 RPM for 5 seconds and not in fuel shut off.
The TFP manual valve position switch indicates an invalid switch combination for 60 seconds.

Condition 2

No VSS DTC P0502 or P0503.
The vehicle speed is less than 5 km/h (3 mph).
TFP manual valve position switch indicates REVERSE, D2 or D4 for 7 seconds at engine start up without indicating PARK or NEUTRAL.
The engine speed transitions from less than 50 RPM to greater than 700 RPM indicating start up.

Condition 3

No TP sensor DTC P0121, P0122 or P0123.
No VSS DTC P0502 or P0503.
No AT ISS sensor DTC P0716 or P0717.
No 1-2, 3-4 SS valve DTC P0751, P0752 or P0753.
No 2-3 SS valve DTC P0756, P0757 or P0758.
The engine speed is greater than 500 RPM for 5 seconds and not in fuel shut off.
The TP angle is greater than 9%.
The vehicle speed is more than 8 km/h (5 mph). The engine torque is greater than 70 Nm (50 ft. Lbs.) And one of the following conditions occurs:
The gear ratio indicates REVERSE, D4, D3, D2 or D1 and the TFP manual valve position switch indicates PARK or NEUTRAL for 5 seconds.
The gear ratio indicates D4, D3, D2 or D1 and the TFP manual valve position switch indicates REVERSE for 5 seconds.
The gear ratio indicates REVERSE and the TFP manual valve position switch indicates D4, D3, D2 or D1 for 5 seconds.

Action Taken When the DTC Sets

The PCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met.
The PCM commands maximum line pressure.
The PCM freezes shift adapts.
The PCM assumes D4 for shifting.
The PCM records the operating conditions when the Conditions for Setting the DTC are met. The PCM stores this information as Freeze Frame and Failure Records.
The PCM stores DTC P1810 in PCM history during the second consecutive trip in which the Conditions for Setting the DTC are met.

Conditions for Clearing the MIL/DTC

The PCM turns OFF the MIL during the third consecutive trip in which the diagnostic test runs and passes.
A scan tool can clear the MIL/DTC.
The PCM clears the DTC from PCM history if the vehicle completes 40 warm-up cycles without an emission-related diagnostic fault occurring.
The PCM cancels the DTC default actions when the ignition switch is OFF long enough in order to power down the PCM.

Test Description
The numbers below refer to the step numbers on the diagnostic table.

This step tests the indicated range signal to the manual valve range actually selected.

This step tests for correct voltage from the PCM to the transmission 20-way connector.
This step tests for a short together between signal circuit A and signal circuits B or C.

DTC P1810