P0843

DTC P0842 or P0843

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.



DTC Descriptors
DTC P0842
- Transmission Fluid Pressure (TFP) Switch 1 Circuit Low Voltage

DTC P0843
- Transmission Fluid Pressure (TFP) Switch 1 Circuit High Voltage




Diagnostic Fault Information






Typical Scan Tool Data






Circuit/System Description

The transmission fluid pressure (TFP) switch 1 is part of the control solenoid (w/body and TCM) valve assembly and has no serviceable parts. The TCM supplies 12-volts to the TFP Switch 1 on the TFP Switch 1 signal circuit. The TFP Switch 1 has an internal case ground. TFP Switch 1 is normally closed, Low. When oil pressure is present at the TFP Switch 1, the switch is Open, High. The normally high clutch pressure control (PC) solenoid 2 controls the transmission fluid to the 3-5-R clutch. The TCM monitors the normally closed TFP Switch 1 signal circuit to determine the 3-5-R clutch status.


Conditions for Running the DTC

* No DTCs P0120, P0711, P0712, or P0713.
* No DTCs P0965, P0966, P0967, P0968, P0969, P0970, or P0971.
* No DTCs P0973, P0974, P0976, P0977, P2719, P2720, P2728, P2729, or P2730.
* No DTCs P1825 or P1915.
* Ignition voltage is between 11-15 volts.
* The transmission fluid temperature (TFT) is 20-150°C (68-302°F).



Conditions for Setting the DTC

P0842

The TCM detects that the TFP switch 1 signal voltage remains low, 0 volts when the 3-5-R clutch is commanded ON.

P0843

The TCM detects that the TFP switch 1 signal voltage is high, 12 volts when the 3-5-R clutch is commanded OFF.


Action Taken When the DTC Sets

* DTCs P0842 and P0843 are Type C DTCs.
* The TCM freezes transmission adaptive functions.



Conditions for Clearing the DTC

DTCs P0842 and P0843 are Type C DTCs.


Reference Information
Schematic Reference

Automatic Transmission Controls Schematics (Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector Views)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Description and Operation

Transmission Component and System Description (Transmission Component and System Description)
DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Diagnostic Trouble Code Descriptions)
Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information


Circuit/System Verification

If there are any other transmission related DTCs set, diagnose those DTCs first.


Circuit/System Testing

1. Ensure the TFT is near the temperature displayed in the Failure Records.
2. Start the engine and observe the TFP Switch 1 parameter while moving the range selector lever from Park to Reverse. The TFP Switch 1 should transition from Hi in Park to Low in Reverse.

• If the TFP Switch 1 parameter does not change, perform the Control Solenoid Valve and Transmission Control Module Assembly Inspection (Control Solenoid Valve and Transmission Control Module Assembly Inspection) .
• If no concerns are found, replace the control solenoid valve and TCM assembly.




Component Testing

Perform the Control Solenoid Valve and Transmission Control Module Assembly Inspection (Control Solenoid Valve and Transmission Control Module Assembly Inspection) .


Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* control solenoid (w/body and TCM) valve assembly replacement. Refer to Control Module References (Programming and Relearning) for replacement, setup, and programming.
* Perform the Service Fast Learn Adapts (Programming and Relearning) if internal transmission repairs are performed.