6T70/6T75 - 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
Circuit/System Description
The transmission fluid pressure (TFP) switch assembly is part of the control solenoid (w/body and TCM) valve assembly and is not serviced separately. The transmission control module (TCM) supplies 12 volts to each TFP switch via its respective signal circuit. The TFP switch assembly has an internal case ground. Each TFP switch is normally closed, Low. When oil pressure is present at the TFP switch, the switch is Open, High. The TCM monitors each normally closed TFP switch signal circuit to determine 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 P0977.
* No IMS DTCs P1825, P182E, or P1915.
* The engine speed is 1,100 RPM or greater.
* Ignition voltage is between 8.6-19.0 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.
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 failure 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 6T70/6T75 - Automatic Transmission
Description and Operation
* Transmission General Description Transmission General Description
* Electronic Component Description Electronic Component Description for control solenoid (w/body and TCM) valve assembly
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References Programming and Relearning for scan tool information
Circuit/System Verification
1. If there are any other transmission related DTCs set, diagnose those DTCs first. Refer to Diagnostic Trouble Code (DTC) List - Vehicle Diagnostic Trouble Code (DTC) List - Vehicle.
2. Engine idling, parking brake applied, range selector in D, command the Shift Transmission with a scan tool to achieve 2nd gear.
3. Observe the suspect scan tool TFP Switch parameter while commanding the Shift Transmission with a scan tool to achieve 5th gear. Each TFP Switch parameter should toggle states (from High to Low or Low to High) between 2nd and 5th gear.
• If the specified parameter does not toggle, replace the control solenoid (w/body and TCM) valve assembly.
Repair Instructions
Note:
* Perform the Service Fast Learn Adapts 6T70/6T75 - Automatic Transmission following all transmission related repairs.
* Before replacing the TCM, perform the Control Solenoid Valve and Transmission Control Module Assembly Inspection Control Solenoid Valve and Transmission Control Module Assembly Inspection.
Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.
Control Module References Programming and Relearning for control solenoid (w/body and TCM) valve assembly replacement, setup, or programming