6T70/6T75 - Automatic Transmission
DTC P0842 or P0843
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* Review Strategy Based Diagnosis for an overview of the diagnostic approach.
* 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 (w/body and TCM) valve assembly and is not serviced separately. 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 TFT DTCs P0711, P0712, or P0713.
* No pressure control solenoid electrical DTCs P0965, P0966, P0967, P0969, P0970, P0971, P2719, P2720, P2721, P2728, P2729, or P2730.
* No shift solenoid electrical DTCs P0973, P0974, P0976, or P09770.
* No IMS DTCs P1825 or P1915.
* The engine speed is 1,100 RPM or greater.
* Ignition voltage is between 8.6 volts and 19.0 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 for 5.5 seconds or greater.
P0843
The TCM detects that the TFP switch 1 signal voltage is high, 12 volts when the 3-5-R clutch is commanded OFF for 5.5 seconds or greater.
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.
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 after completing the diagnostic procedure. Verification Tests
1. Control solenoid (w/body and TCM) valve assembly replacement. Refer to Programming and Relearning for replacement, setup, and programming.
2. Perform the Service Fast Learn Adapts. Programming and Relearning