GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2008 🢒 Sierra Denali 🢒 DTC 🢒 DTC P1810, P1815, P1816, or P1818

Diagnostic Instructions
    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC P1810: Transmission Fluid Pressure (TFP) Position Switch Circuit

DTC P1815: Transmission Fluid Pressure (TFP) Valve Position Switch - Start in Wrong Range

DTC P1816: Transmission Fluid Pressure (TFP) Valve Position Switch Indicates Park/Neutral (P/N) with Drive Ratio

DTC P1818: Transmission Fluid Pressure (TFP) Valve Position Switch Indicates Drive without Drive Ratio

Circuit/System Description

The automatic transmission fluid pressure (TFP) manual valve position switch consists of 5 pressure switches and a transmission fluid temperature (TFT) sensor combined into one unit. The combined unit mounts on the valve body. The transmission control module (TCM) supplies ignition voltage for each range signal. By grounding one or more of these circuits through various combinations of the pressure switches, the TCM detects which manual valve position you select. The TCM 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. With the engine OFF and the ignition switch in the ON position, the TFP manual valve position switch indicates PARK/NEUTRAL. Disconnecting the 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.

Conditions for Running the DTC

P1810

The engine speed is greater than 500 RPM for 5 seconds.

P1815

    • No output speed sensor (OSS) DTCs P0722, or P0723.
    • The system voltage is 8-18 volts.
    • OSS speed is 250 RPM or less.

P1816

    • No input speed sensor (ISS) DTCs P0716 or P0717.
    • No OSS DTCs P0722, or P0723.
    • No SS DTCs P0751, P0752, P0756, P0757, P0973, P0974, P0976 or P0977.
    • No TFP DTCs P1810, P1815 or P1818.
    • The engine torque is greater than 50 N·m (37 lb ft).
    • The output speed is 350 RPM or greater.
    • OSS speed is 350 RPM or greater.
    • The throttle position is 8 percent or greater.

P1818

    • No OSS DTCs P0722, or P0723.
    • No TFP DTCs P1810, P1815 or P1816.
    • The throttle position is 8 percent or greater.
    • The engine torque is 20 N·m (15 lb ft) or greater.
    • OSS speed is 50 RPM or greater.

Conditions for Setting the DTC

P1810

The TCM detects an invalid TFP manual valve position switch state for 60 seconds.

P1815

The TCM detects D2 only, TFP manual valve position switch state during and after engine start for 3.25 seconds.

P1816

The TCM detects one of the following conditions for 6 seconds.

    • PARK/NEUTRAL indicated with a 1st gear ratio.
    • PARK/NEUTRAL indicated with a 2nd gear ratio.
    • PARK/NEUTRAL indicated with a 3rd gear ratio.
    • PARK/NEUTRAL indicated with a 4th gear ratio.

P1818

The TCM detects the following condition for 5 seconds.

PARK/NEUTRAL or FORWARD range indicated with a reverse gear ratio.

Action Taken When the DTC Sets
    • DTCs P1810, P1815, P1816 and P1818 are Type B DTCs.
    • The TCM commands maximum line pressure.
    • The TCM freezes transmission adaptive functions.

Conditions for Clearing the DTC

DTCs P1810, P1815, P1816, P1818 are Type B DTCs.

Diagnostic Aids
    • Refer to the Transmission Fluid Pressure Manual Valve Position Switch Logic for the normal range signals and the invalid combinations. On the table, LOW is 0 volts, HI is ignition voltage.
    • Sediment in the valve body may cause improper operation of the TFP manual valve position switch. If sediment intrusion is suspected, clean the valve body and replace the TFP manual valve position switch.

Reference Information

Schematic Reference

Automatic Transmission Controls Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Transmission General Information

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Transmission Control Module Scan Tool Information

Special Tools

J 44152 Jumper Harness (20 Pins)

Circuit/System Verification
  1. Perform the Transmission Fluid Check to verify correct fluid level and condition. The transmission fluid level should be within the crosshatch band and the transmission fluid should be red or dark brown.
    2. ⇒If the transmission fluid is low or discolored, refer to Automatic Transmission Fluid and Filter Replacement .
  2. Engine idling, observe the scan tool TFP Sw. A/B/C parameter while moving the gear shift lever from Park, to Reverse and through all the gear ranges and compare to the Transmission Fluid Pressure Manual Valve Position Switch Logic table. The parameter should match each gear range that is selected.
  3. Observe the scan tool TFP Sw. parameter while moving the gear shift lever from Park, to Reverse and through all the gear ranges. The selected transmission gear range should match the scan tool TFP Sw. display.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing

Important: Additional DTCs may set when disconnecting the automatic transmission inline 20-way connector.

  1. Ignition OFF, disconnect the automatic transmission (AT) inline 20-way connector at the transmission.
  2. Install the J 44152 on the engine side of the AT inline 20-way connector.
  3. Ignition ON, observe the scan tool TFP Sw. A/B/C parameter. The reading should display HI/HI/HI.
    4. ⇒If not the specified value, test the appropriate signal circuit for a short to ground. If the circuits test normal, replace the TCM.
  4. Test for B+ between each signal circuit terminals N, R, P and ground.
    5. ⇒If less than the specified value, test the appropriate signal circuit for an open/high resistance. If the circuits test normal, replace the TCM.
  5. If all circuits test normal, test the automatic transmission internal wiring harness and the TFP switch.

Component Testing
  1. Ignition OFF, disconnect the AT inline 20-way connector at the transmission.
  2. Install the J 44152 on the transmission side of the AT inline 20-way connector.
  3. Test the signal A circuit terminal N for less than 10 ohms of resistance with the transmission in Reverse and infinite resistance with transmission in Park.
    4. ⇒If not the specified value, test the signal circuit for a short to ground, a short to voltage, or open/high resistance. If a circuit is shorted or open, replace the internal transmission harness, if the circuits test normal, replace the TFP switch.
  4. Test the signal B circuit terminal R for less than 10 ohms of resistance with the transmission in Park and infinite resistance with transmission in Drive 3.
    5. ⇒If not the specified value, test the signal circuit for a short to ground, a short to voltage, or open/high resistance. If a circuit is shorted or open, replace the internal transmission harness, if the circuits test normal, replace the TFP switch.
  5. Test the signal C circuit terminal P for less than 10 ohms of resistance with the transmission in Drive 4 and infinite resistance with transmission in Park.
    6. ⇒If not the specified value, test the signal circuit for a short to ground, a short to voltage, or open/high resistance. If a circuit is shorted or open, replace the internal transmission harness, if the circuits test normal, replace the TFP switch.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

    •  Valve Body and Pressure Switch Replacement
    • Refer to Control Module References for TCM replacement, setup, and programming