GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Isuzu 🢒 2009 🢒 Isuzu - N Series 🢒 DTC 🢒 DTC P1810, 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 Descriptors

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

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 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 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 automatic transmission 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.
    • The system voltage is 8-18 volts.
    • Power take-off (PTO) is not active.

P1816

    • DTCs P0716, P0717, P0722, P0723, P0751, P0752, P0756, P0757, P0973, P0974, P0976, P0977, P1810, or P1818 are not set.
    • The engine speed is greater than 500 RPM.
    • The system voltage is 8-18 volts.
    • PTO is not active.
    • The engine torque is greater than 50 N·m (37 lb ft).
    • The output speed is 350 RPM or greater.
    • The OSS speed is 350 RPM or greater.
    • The throttle position is 8 percent or greater.

P1818

    • DTCs P0722, P0723, P1810, or P1816 are not set.
    • The engine speed is greater than 500 RPM.
    • The system voltage is 8-18 volts.
    • The throttle position is 8 percent or greater.
    • The engine torque is greater than 50 N·m (37 lb ft).
    • The OSS speed is greater than 50 RPM.

Conditions for Setting the DTC

P1810

The TCM detects an invalid TFP manual valve position switch state for 5 seconds.

P1816

The TCM detects one of the following conditions for 4 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 PARK/NEUTRAL or FORWARD range with a REVERSE gear ratio for 5 seconds.

Action Taken When the DTC Sets

DTCs P1810, P1816, and P1818 are type B DTCs.

Conditions for Clearing the DTC

DTCs P1810, P1816, and P1818 are type B DTCs.

Diagnostic Aids
    • Refer to 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

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

Control Module References for scan tool information

Special Tools

    • J 35616 GM-Approved Terminal Test Kit
    • J 44152 Jumper Harness (20 Pins)

Circuit/System Verification

Start and idle the engine. Using the scan tool, observe the TFP Sw A/B/C parameter. The scan tool should display High/Low/High. Move the gear selector through all ranges and ensure the TFP Switch parameter matches the gear selector for each selected range.

Circuit/System Testing
  1. Perform the Transmission Fluid Check .
    2. ⇒If the fluid level is at an incorrect level, repair any leaks found and add fluid to the proper level.
  2. Disconnect the automatic transmission inline 20-way connector. Turn ON the ignition with the engine OFF.
  3. Observe the TFP Sw A/B/C parameter on the scan tool. The parameter should display LO/HI/HI.
    4. ⇒If either B or C display LOW, repair the short to ground in the TFP signal circuit that displayed LOW.
  4. Measure for greater than 12 volts at the engine side of the automatic transmission 20-way connector between the TFP switch signal A circuit terminal N and ground.
    5. ⇒If the voltage is less than the specified range, repair the open circuit. If the circuit tests normal, replace the TCM
  5. Measure for greater than 12 volts at the engine side of the automatic transmission 20-way connector between the TFP switch signal B circuit terminal R and ground.
    6. ⇒If the voltage is less than the specified range, repair the open circuit. If the circuit tests normal, replace the TCM.
  6. Measure for greater than 12 volts at the engine side of the automatic transmission 20-way connector between the TFP switch signal C circuit terminal P and ground.
    7. ⇒If the voltage is less than the specified range, repair the open circuit. If the circuit tests normal, replace the TCM
  7. Ignition OFF, measure for greater than 10K ohms of resistance at the transmission side of the automatic transmission 20-way connector between the TFP signal A circuit terminal N and the transmission case.
    8. ⇒If the resistance is less than 10K ohms, test the transmission wiring harness for a short to ground. If the harness tests normal, replace the TFP switch.
  8. Ignition OFF, measure for greater than 10K ohms of resistance at the transmission side of the automatic transmission 20-way connector between the TFP signal B circuit terminal R and the transmission case.
    9. ⇒If the resistance is less than 10K ohms, test the transmission wiring harness for a short to ground. If the harness tests normal, replace the TFP switch.
  9. Ignition OFF, measure for greater than 10K ohms of resistance at the transmission side of the automatic transmission 20-way connector between the TFP signal C circuit terminal P and the transmission case.
    10. ⇒If the resistance is less than 10K ohms, test the transmission wiring harness for a short to ground. If the harness tests normal, replace the TFP switch.

Component Testing
  1. Disconnect the automatic transmission 20-way connector. Measure the resistance between the TFP signal B circuit and the TFP signal C circuit at the transmission side of the automatic transmission 20-way connector and ground. The resistance should be greater than 10K ohms.
    2. ⇒If the resistance is not greater than the specified range, test the affected circuit for a short to ground.
    ⇒If a short to ground is not found, replace the TFP switch.
  2. Start the engine. Measure the resistance between the TFP signal B circuit and the TFP signal C circuit at the transmission side of the automatic transmission 20-way connector and ground. The resistance should be less than 10 ohms.
    3. ⇒If the resistance is greater than 10 ohms, test the affected circuit for an open.
    ⇒If an open circuit is not found, replace the TFP switch.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

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