DTC P1808 or P1809 Hybrid

Diagnostic Instructions

DTC Descriptors

DTC P1808:  Transmission Fluid Pressure (TFP) Position Switch - Stuck Off

DTC P1809:  Transmission Fluid Pressure (TFP) Position Switch - Stuck On

Circuit/System Description

The automatic transmission fluid pressure (TFP) manual valve position switch consists of four pressure switches. Two of the switches are normally-open, and determine gear range selection. A third switch is used to determine if the transmission has line pressure for Hybrid operation. The fourth switch is normally-closed, and detects torque converter clutch (TCC) release fluid pressure. The TFP manual valve position switch also contains the automatic transmission fluid temperature (TFT) sensor. These components are combined into one unit, attached to the control valve body.

The transmission control module (TCM) provides battery voltage on the two range signal circuits. By grounding one or more of switches B and C with fluid pressure from the manual shift valve, the TCM detects the selected gear range. Switch A indicates to the engine control module (ECM) if there is line pressure, from either the transmission or the auxiliary trans pump, and allows hybrid operation. When you disconnect the transmission electrical connector and the ignition is ON, the ground potential for the range signals from the TCM/ECM will be removed, and an invalid gear range will be indicated.

Conditions for Running the DTC

Calibrated For a Normally-Open TFP Switch A:

P1808

P1809

Calibrated For a Normally-Closed TFP Switch A:

P1808

P1809

Conditions for Setting the DTC

P1808

The ECM determines that the TFP signal A circuit is open or stuck OFF.

P1809

The ECM determines that the TFP signal A circuit is shorted to ground or stuck ON.

Action Taken When the DTC Sets

Conditions for Clearing the DTC

DTCs P1808 and P1809 are Type B DTCs.

Reference Information

Schematic Reference

Automatic Transmission Controls Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Electronic Component Description for automatic transmission fluid pressure manual valve position switch assembly information.

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for 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.

⇒	If the transmission fluid is low or discolored, replace the transmission fluid.

2. Ignition ON, engine off, gear selector in Park, Reverse, Neutral, or Drive, observe the scan tool ECM TFP switch A parameter should read Low. Engine running, observe the scan tool ECM TFP switch A parameter should read High.
3. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observe from the Freeze Frame/Failure Records data.

Circuit/System Testing

Important: If the above Circuit/System Verification results in inverted operation, check for a calibration/switch mismatch.

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

Normally-Open TFP Switch A:

1. Ignition OFF, disconnect the AT 20-way inline harness connector at the transmission.
2. Ignition ON, verify the scan tool ECM TFP Switch A parameter is Low.

⇒	If not the specified value, test the signal circuit terminal N for a short to ground. If the circuit tests normal, replace the ECM.

3. Install a 3A fused jumper wire between the signal circuit terminal N to ground. Verify the scan tool TFP Switch A is High.

⇒	If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.

4. Test for less than 1 ohm of resistance between terminal N of the AT 20-way connector and terminal A of the TFP manual valve position switch.

⇒	If greater than the specified range, replace the Internal Transmission Harness.

5. If all circuits test normal, test or replace the TFP switch.

Normally-Closed TFP Switch A:

1. Ignition OFF, disconnect the AT 20-way inline harness connector at the transmission.
2. Ignition ON, verify the scan tool ECM TFP Switch A parameter is High.

⇒	If not the specified value, test the signal circuit terminal N for a short to ground. If the circuit tests normal, replace the ECM.

3. Install a 3A fused jumper wire between the signal circuit terminal N to ground. Verify the scan tool TFP Switch A is Low.

⇒	If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.

4. Test for less than 1 ohm of resistance between terminal N of the AT 20-way connector and terminal A of the TFP manual valve position switch.

⇒	If greater than the specified range, replace the Internal Transmission Harness.

5. If all circuits test normal, test or replace the TFP switch.

Component Testing

Normally-Open TFP Switch A:

With the TFP switch removed from the transmission test for infinite resistance between the control terminal A and the metal mounting bracket of the TFP switch, and less than 5 ohms of resistance while depressing the switch.

Normally-Closed TFP Switch A:

With the TFP switch removed from the transmission test for less than 5 ohms of resistance between the control terminal A and the metal mounting bracket of the TFP switch, and infinite resistance while depressing the switch.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.