For 1990-2009 cars only
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 Descriptors
DTC P0843: Transmission Pressure Switch 1 Circuit HighDTC P0848: Transmission Pressure Switch 2 Circuit High
DTC P0873: Transmission Pressure Switch 3 Circuit High
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
PS1 Signal | P0752, P0842 | P0751, P0843 | -- | -- |
PS2 Signal | P0757, P0847 | P0756, P0848 | -- | -- |
PS3 Signal | P0762, P0872 | P0761, P0873 | -- | -- |
Typical Scan Tool Data
Display Parameters | Normal Range | Short to Ground | Open/High Resistance | Short to Voltage |
|---|---|---|---|---|
Operating Conditions: Ignition ON, engine OFF | ||||
TFP Switch 1 | High | Low | High | -- |
TFP Switch 2 | High | Low | High | -- |
TFP Switch 3 | High | Low | High | -- |
Operating Conditions: Engine running, transmission in park or neutral position | ||||
TFP Switch 1 | Low | Low | High | -- |
TFP Switch 2 | Low | Low | High | -- |
TFP Switch 3 | Low | Low | High | -- |
Circuit/System Description
The pressure switch manifold (PSM) is a multiple switch assembly made up of 3 normally open (N/O) pressure switches and 1 normally closed (N/C) pressure switch. Pressure switch 1 (PS1) monitors shift valve 1 positioning, pressure switch 2 (PS2) monitors shift valve 2 positioning, and pressure switch 2 (PS3) monitors shift valve 3 positioning. The pressure switches communicate the positioning to the transmission control module (TCM).
Conditions for Running the DTC
P0843
| • | The ignition is ON. |
| • | Ignition voltage is greater than 9.0 V and less than 18 V. |
| • | Engine speed is greater than 200 RPM and less than 7500 RPM for 5 seconds. |
| • | Shift valve 1 is commanded to the ON, or stroked position. |
P0848
| • | The ignition is ON. |
| • | Ignition voltage is greater than 9.0 V and less than 18 V. |
| • | Engine speed is greater than 200 RPM and less than 7500 RPM for 5 seconds. |
| • | Shift valve 2 is commanded to the ON, or stroked position. |
P0873
| • | The ignition is ON. |
| • | Ignition voltage is greater than 9.0 V and less than 18 V. |
| • | Engine speed is greater than 200 RPM and less than 7500 RPM for 5 seconds. |
| • | Shift valve 3 is commanded to the ON, or stroked position. |
Conditions for Setting the DTC
P0843
This DTC sets during steady state operation when shift solenoid 1 (SS1) is commanded ON and PS1 indicates OFF for 1 second.
P0848
This DTC sets during steady state operation when shift solenoid 2 (SS2) is commanded ON and PS1 indicates OFF for 1 second.
P0873
This DTC sets during steady state operation when shift solenoid 3 (SS3) is commanded ON and PS1 indicates OFF for 1 second.
Action Taken When the DTC Sets
P0843
| • | The TCM requests the ECM to illuminate the malfunction indicator lamp (MIL). |
| • | When in a forward range and shifting is completed, the transmission will shift to another forward range, unless the transmission is compromised by overspeeding or direction change, then the transmission will shift to NEUTRAL. |
| • | When in a forward range and the shift is in process the transmission will return to a previous range, except for 1-2 shifts and 2-1 shifts which will be completed. |
| • | While diagnostic response is active, when the shift selector is moved from a forward range to NEUTRAL or from a forward range to REVERSE, then the transmission will shift to NEUTRAL. |
| • | DTC P0843 is stored in TCM history. |
| • | The TCM freezes shift adapts. |
| • | The TCM inhibits torque converter clutch (TCC) engagement. |
P0848
| • | The TCM requests the ECM to illuminate the MIL. |
| • | When in a forward range and shifting is completed, the transmission will shift to another forward range, unless the transmission is compromised by overspeeding, then the transmission will shift to NEUTRAL. |
| • | While diagnostic response is active, when the shift selector is moved from a forward range or reverse to NEUTRAL, the transmission will shift to neutral. If the shift selector is moved to reverse, then the transmission will shift to REVERSE unless the transmission is compromised by overspeeding or a direction change. |
| • | DTC P0848 is stored in TCM history. |
| • | The TCM freezes shift adapts. |
| • | The TCM inhibits TCC engagement. |
P0873
| • | The TCM requests the ECM to illuminate the MIL. |
| • | When in a forward range and shifting is completed, the transmission will shift to another forward range, unless the transmission is compromised by overspeeding then the transmission will shift to NEUTRAL. |
| • | While diagnostic response is active, when the shift selector is moved from a forward range to NEUTRAL, the transmission will shift to neutral. If the shift selector is moved to reverse, then the transmission will shift to REVERSE unless the transmission is compromised by overspeeding or a direction change. |
| • | DTC P0873 is stored in TCM history. |
| • | The TCM freezes shift adapts. |
| • | The TCM inhibits TCC engagement. |
Conditions for Clearing the DTC
DTCs P0843, P0848, and P0873 are Type A DTCs.
Diagnostic Aids
P0843
| • | If DTC P0701 is set in combination with DTC P0843, diagnose P0701 prior to proceeding to DTC P0843. |
| • | You may have to drive the vehicle in order to experience a condition. |
| • | This DTC may indicate that SS1 is mechanically defective. |
| • | When DTCs P0751 and P0843 are set in combination, this may indicate an open circuit condition on the pressure switch 1 circuit or the shift valve 1 is stuck in the destroked position. |
| • | This DTC can be caused by a loss of prime. |
| • | This DTC can be caused by a plugged control main filter. |
P0848
| • | If DTC P0701 is set in combination with DTC P0848, diagnose P0701 prior to proceeding to DTC P0848. |
| • | You may have to drive the vehicle in order to experience a condition. |
| • | This DTC may indicate that SS2 is mechanically defective. |
| • | When DTCs P0756 and P0848 are set in combination, this may indicate an open circuit condition on the pressure switch 2 circuit or the shift valve 2 is stuck in the destroked position. |
| • | This DTC can be caused by a loss of prime. |
| • | This DTC can be caused by a plugged control main filter. |
P0873
| • | If DTC P0701 is set in combination with DTC P0873, diagnose P0701 prior to proceeding to DTC P0873. |
| • | You may have to drive the vehicle in order to experience a condition. |
| • | This DTC may indicate that SS3 is mechanically defective. |
| • | When DTCs P0761 and P0873 are set in combination, this may indicate an open circuit condition on the pressure switch 3 circuit or the shift valve 3 is stuck in the destroked position. |
| • | This DTC can be caused by a loss of prime. |
| • | This DTC can be caused by a plugged control main filter. |
Reference Information
Schematic Reference
Automatic Transmission Controls Schematics
Connector End View Reference
Description and Operation
Electrical Information Reference
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
- If DTC P0701 is set, diagnose first. Refer to DTC P0701.
- Engine running, command the transmission through the forward ranges with a scan tool. Compare the TFP Switch 1, TFP Switch 2, and TFP Switch 3 parameters in each forward range with the Pressure Switch Manifold Logic table. Refer to Pressure Switch Manifold (PSM) Logic.
- Operate the vehicle within the Conditions for Running the DTC to verify the DTC 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
- Inspect the transmission fluid level. Refer to Transmission Fluid Check.
- Ignition OFF, disconnect the X175 harness connector at the transmission.
- Ignition ON, engine OFF, connect a 3A fused jumper wire to the PS1 signal circuit terminal D to ground, PS2 signal circuit terminal F to ground, and PS3 signal circuit terminal E to ground. Verify with a scan tool the TFP Switch 1, TFP Switch 2, and TFP Switch 3 parameters changed from High to Low when the signal circuit is grounded.
- Ignition OFF, connect the X175 harness connector to the transmission.
- Remove the pressure switch module from the valve body. Leave the internal wire harness connected to the pressure switch manifold. Refer to Pressure Switch Manifold Replacement.
- Connect a jumper wire to the base of the pressure switch module and ground.
- Ignition ON, engine OFF, gently push on the PS1, PS2, and PS3 switches. Verify with a scan tool that TFP Switch 1, TFP Switch 2, and TFP Switch 3 parameters changed from High to Low.
- If all circuits test normal, refer to refer to Control Valve Body Assembly Disassemble and Control Valve Body Cleaning and Inspection.
| ⇒ | If not the specified value, test the affected pressure switch signal circuit for an open/high resistance. If circuits test normal, replace the TCM. |
| ⇒ | If not the specified value, test the internal wire harness circuits for an open/high resistance. If the circuits test normal, replace the pressure switch module. |
| ⇒ | If valve body inspection is normal, replace the shift solenoid indicated by the DTC, refer to Control Valve Solenoid Replacement. |
Component Testing
Static Testing
- Ignition OFF, remove the PSM from the valve body. Refer to Pressure Switch Manifold Replacement.
- Test for resistance between the PS1 circuit terminal X and the metal base of the PSM. Resistance should be greater than 10 K ohms. If not, replace the PSM.
Note: You must perform the Circuit/System Testing first.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for TCM replacement, setup, and programming |
Repair Verification
If another DTC is present, refer to Diagnostic Trouble Code (DTC) List - Vehicle and perform the appropriate diagnostic procedure.
