6L50/6L80/6L90 - Automatic Transmission
DTC P0842 or P0843
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions)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 valve assembly which has no serviceable parts. The TCM supplies a signal circuit to the TFP Switch 1. The TFP Switch 1 has an internal case ground. TFP Switch 1 is normally closed or LOW. When oil pressure is present at the TFP Switch 1, the switch is open or HIGH. The normally high clutch pressure control (PC) solenoid 2 controls pressure to the 3-5 reverse clutch regulator valve. The TCM monitors the TFP switch 1 to determine the position of the 3-5 reverse clutch regulator valve. When the 3-5 reverse clutch is commanded OFF, pressure is present on the TFP switch 1. When the 3-5 reverse clutch is commanded ON, the 3-5 reverse clutch regulator valve moves and pressure to the TFP switch 1 is exhausted through the 3-5 reverse clutch regulator valve.
Conditions for Running the DTC
P0842 or P0843
* No other ECM or TCM DTCs are set.
* Ignition voltage is 8.6 volts or greater.
* The transmission fluid temperature (TFT) is -6.6°C (20°F).
* Engine speed is 400 RPM or greater for 5 seconds.
* The high side driver is commanded ON.
Conditions for Setting the DTC
P0842
The TCM detects that the TFP switch 1 signal voltage remains LOW after the 3-5-R clutch transitions from a HIGH pressure state to a LOW pressure state. The TCM counts each incident. The DTC sets when 25 counts are accumulated.
P0843
The TCM detects that the TFP switch 1 signal voltage remains HIGH after the 3-5-R clutch transitions from a LOW pressure state to a HIGH pressure state. The TCM counts each incident. The DTC sets when 24 counts are accumulated.
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.
Diagnostic Aids
A TFP switch may malfunction due to normal debris in the transmission fluid causing a TFP Switch DTC to intermittently set. This type of condition should not be immediately noticeable to a customer, as the switch outputs are used for shift adaptive pressure and do not cause transmission symptoms unless the switch malfunctions continuously for an extended period of time.
Reference Information
Schematic Reference
Automatic Transmission Controls Schematics (6L45/6L50/6L80/6L90 - Automatic Transmission)
Connector End View Reference
* Component Connector End Views (Connector End Views By Name)
* Inline Harness Connector End Views (Connector End Views By Number)
Electrical Information Reference
* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)
Description and Operation
* Electronic Component Description (Electronic Component Description)
* Transmission General Description (Transmission General Description)
* Transmission Component and System Description (Transmission Component and System Description)
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Powertrain Diagnostic Trouble Code (DTC) Type Definitions)
Scan Tool Reference
Control Module References (Control Module References)for scan tool information
Special Tool Reference
DT-47825-10 - Jumper Harness
Circuit/System Verification
1. Engine idling in Park with parking brake applied, and drive wheels chocked.
2. Monitor the Transmission Fluid Pressure Switch 1, Transmission Fluid Pressure Switch 3, Transmission Fluid Pressure Switch 4, and Transmission Fluid Pressure Switch 5 parameters with a scan tool.
3. Place the gear select lever in Park, Reverse, and Neutral range. Verify the TFP switch parameter states are correct for each range. Refer to Transmission Fluid Pressure Switch Logic (Transmission Fluid Pressure Switch Logic).
4. Place the gear select lever in Drive range. Command the shift transmission with a scan tool through all forward ranges. Verify the TFP switch parameter states are correct for each range. Refer to Transmission Fluid Pressure Switch Logic (Transmission Fluid Pressure Switch Logic).
5. Operate the vehicle within the conditions for running the DTC to verify the TDC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
Circuit/System Testing
Note: You must perform the Circuit/System Verification first.
1. Ignition OFF. Remove the Q8 control solenoid valve assembly. Refer to Control Valve Body Assembly Removal (4. Control Valve Body Assembly Removal).
2. Perform the Control Solenoid Valve and Transmission Control Module Assembly Inspection (Control Solenoid Valve and Transmission Control Module Assembly Inspection).
3. Place the Q8 control solenoid valve assembly on a clean work surface near the transmission assembly.
4. Connect the DT-47825-10 - jumper harness between the vehicle wire harness electrical connector, and the Q8 control solenoid valve assembly electrical connector.
5. Ignition ON, verify with a scan tool that each TFP switch parameter changes states when gently pushing on each TFP switch with the eraser end of a pencil.
• If any TFP switch parameter does not change states, replace the Q8 control solenoid valve assembly.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* control solenoid valve assembly replacement. Refer to Control Module References (Control Module References) for replacement, setup, and programming.
* Perform the Service Fast Learn Adapts (6L45/6L50/6L80/6L90 - Automatic Transmission) following all transmission related repairs.