Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
DTC Descriptor
DTC P0842: Transmission Fluid Pressure (TFP) Switch 1 Circuit Low VoltageDTC P0843: Transmission Fluid Pressure (TFP) Switch 1 Circuit High Voltage
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
TFP Switch 1 Signal | P0842 | P0843 | P0843 | -- |
TFP Switch 3 Signal | P0872 | P0873 | P0873 | -- |
TFP Switch 4 Signal | P0877 | P0878 | P0878 | -- |
TFP Switch 5 Signal | P0989 | P0990 | P0990 | -- |
Typical Scan Tool Data
TFP Switches
Circuit | Short to Ground | Open/High Resistance | Short to Voltage |
|---|---|---|---|
Operating Conditions: Engine running, normal operating temperature Parameter Normal Range: 12 Volts = Hi, 0 Volts = Low | |||
TFP Switch 1 | Low | Hi | Hi |
TFP Switch 3 | Low | Hi | Hi |
TFP Switch 4 | Low | Hi | Hi |
TFP Switch 5 | Low | Hi | Hi |
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 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 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.
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
Connector End View Reference
Electrical Information Reference
| • | Circuit Testing. |
| • | Connector Repairs. |
| • | Wiring Repairs. |
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
- If there are any other transmission related DTCs set, diagnose those DTCs first. Refer to Diagnostic Trouble Code (DTC) List - Vehicle.
- Perform the Control Solenoid Valve and Transmission Control Module Assembly Cleaning procedure to dislodge debris and free up valves.
- Engine idling, parking brake applied, range selector in D, command the Shift Transmission with a scan tool to achieve 2nd gear.
- 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. |
Circuit/System Testing
- Ensure the TFT is near the temperature displayed in the Failure Records.
- 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. |
| ⇒ | 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.
Repair Instructions
Important: Always perform the Diagnostic Repair Verification after completing the diagnostic procedure.
Control solenoid (w/body and TCM) valve assembly replacement. Refer to Control Module References for replacement, setup, and programming.
