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 P0877: Transmission Fluid Pressure (TFP) Switch 4 Circuit Low VoltageDTC P0878: Transmission Fluid Pressure (TFP) Switch 4 Circuit High Voltage
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
PS4 Signal | P0877 | P0878 | -- | -- |
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 4 | Low | Low | High | -- |
Operating Conditions: Engine running, transmission in reverse | ||||
TFP Switch 4 | High | Low | High | -- |
Operating Conditions: Engine running, transmission in park or neutral position | ||||
TFP Switch 4 | 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 4 (PS4) monitors the manual selector valve positioning, and communicates the positioning to the transmission control module (TCM).
Conditions for Running the DTC
P0877
| • | Engine running. |
| • | Battery voltage is greater than 9.0 V and less than 18 V. |
| • | Transmission fluid temperature is above 0°C (32°F). |
| • | TFP switch 4 is low, indicating the manual selector valve is in the reverse. |
| • | DTCs P0708 and P0878 are not active. |
P0878 Condition 1
| • | Engine running. |
| • | Battery voltage is greater than 9.0 V and less than 18 V. |
| • | Transmission fluid temperature is above 0°C (32°F). |
| • | TFP switch 4 is high, indicating the manual selector valve is in neutral or forward position. |
| • | DTCs P0708 and P0878 are not active. |
P0878 Condition 2
| • | Engine was cranking or running during this ignition cycle. |
| • | Battery voltage is greater than 9.0 V and less than 18 V. |
| • | Transmission fluid temperature is above 0°C (32°F). |
| • | Automatic transmission input shaft speed, automatic transmission turbine speed, and vehicle speed sensor speed readings are all less than 50 RPM. |
Conditions for Setting the DTC
P0877
This DTC sets when Park (P), Neutral (N), or a forward range is selected and the TFP switch 4 signal is LOW for greater than 1 second.
P0878 Condition 1
This DTC sets when reverse range is selected and the TFP switch 4 signal is HIGH for more than 1 second more than 40 times.
P0878 Condition 2
This DTC sets when engine shutdown is in process and the TFP switch 4 signal is HIGH for more than a period of time that is temperature dependent; 5 seconds for transmission fluid temperatures above 35°C (95°F) to 30 seconds at -20°C (-4°F).
Action Taken When the DTC Sets
P0877
| • | The TCM requests the engine control module (ECM) to illuminate the malfunction indicator lamp (MIL). |
| • | The transmission will either lock to neutral or the transmission will shift to 3rd or 5th range. |
| • | While diagnostic response is active, if shift selector is moved to neutral, the transmission will shift to neutral. If the selector moved to reverse (R), the transmission will shift to REVERSE. If the shift selector is moved to a forward range or reverse and transmission is compromised by overspeeding or direction change, transmission shifts to neutral. If the transmission was locked to neutral, transmission will stay in neutral in any selector position. |
| • | DTC P0877 is stored in TCM history. |
| • | The TCM freezes shift adapts. |
| • | The TCM inhibits torque converter clutch (TCC) engagement. |
P0878
| • | The TCM requests the ECM to illuminate the MIL on the second consecutive occurrence. |
| • | The transmission will either lock to neutral or the transmission will shift to 3rd or 5th range. |
| • | While diagnostic response is active, if shift selector is moved to neutral, the transmission will shift to neutral. If the selector moved to reverse (R), the transmission will shift to REVERSE. If the shift selector is moved to a forward range or reverse and transmission is compromised by overspeeding or direction change, transmission shifts to neutral. If the transmission was locked to neutral, transmission will stay in neutral in any selector position. |
| • | DTC P0878 is stored in TCM history. |
| • | The TCM freezes shift adapts. |
| • | The TCM inhibits TCC engagement. |
Conditions for Clearing the DTC
| • | DTC P0877 is a Type A DTC. |
| • | DTC P0878 is a Type B DTC. |
Diagnostic Aids
P0877
| • | If DTC P0701 is set in combination with DTC P0877, diagnose P0701 prior to proceeding to DTC P0877. |
| • | If DTCs P0877, P0762 and P0708 are set in combination, the DTCs may indicate a problem with the internal mode switch. |
| • | If DTC P0877 is set with DTCs P0701, P0843, P0848, and or P0873, a problem with line pressure may be indicated. |
| • | You may have to drive the vehicle in order to experience a condition. |
P0878
You may have to drive the vehicle in order to experience a condition.
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
- Ignition ON, engine OFF, verify with a scan tool the TFP Switch 4 parameter is Low.
- Engine running, verify with a scan tool the TFP Switch 4 parameter is Low with selector in reverse and High with selector in all other positions.
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, verify with a scan tool the TFP Switch 4 parameter is High.
- Ignition ON, connect a 3A fused jumper wire to the PS4 signal circuit terminal K to ground. Verify with a scan tool the TFP Switch 4 parameter changes from High to Low when the signal circuit is grounded.
- Remove the transmission oil pan. Refer to Oil Pan Replacement.
- Test the transmission internal Pressure Switch 4 signal circuit for a short to ground or open/high resistance.
| ⇒ | If not the specified value, test the PS4 signal circuit for a short to ground. If circuit tests normal, replace the TCM. |
| ⇒ | If not the specified value, test the PS4 signal circuit for an open/high resistance. If the circuit tests normal, replace the TCM. |
| ⇒ | If the circuit tests normal, replace the PSM. Refer to Pressure Switch Manifold Replacement. |
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.
