P0988-4C PRESSURE SWITCH RATIONALITY
For a complete wiring diagram Refer to Section 8W
Theory of Operation
The Transmission system uses five pressure switches to monitor the fluid pressure in the L/R, 2C, 4C, UD, and OD clutch circuits. The pressure switches are continuously monitored for the correct states in each gear as shown.
- When Monitored:
Continuously with the ignition on, engine running, with the transmission in gear.
- Set Condition:
The DTC is set if the 4C Pressure Switch reads open or closed at the wrong time in a given gear .
| Possible Causes |
| RELATED TCM POWER INPUT DTCS PRESENT |
| DTC P0871 ALSO PRESENT |
| LOSS OF 12 VOLT FEED |
| (T48) 4C PRESSURE SWITCH SENSE CIRCUIT OPEN |
| (T48) 4C PRESSURE SWITCH SENSE CIRCUIT SHORT TO GROUND |
| EXCESSIVE FLUID LEAKAGE IN THE 4C CLUTCH CIRCUIT |
| #5 CHECK BALL CUT OR DAMAGED |
| LOW LINE PRESSURE |
| TRANSMISSION SOLENOID/TRS ASSEMBLY |
| POWERTRAIN CONTROL MODULE |
| WIRING AND CONNECTORS |
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - 45RFE/545RFE - DIAGNOSIS AND TESTING) .
| GEAR | L/R | 2C | 4C | UD | OD |
| REVERSE | OPEN | OPEN | OPEN | OPEN | OPEN |
| P/N | CLOSED** | OPEN | OPEN | OPEN | OPEN |
| 1ST | CLOSED* | OPEN | OPEN | CLOSED | OPEN |
| 2ND | OPEN | CLOSED | OPEN | CLOSED | OPEN |
| 2ND PRIME | OPEN | OPEN | CLOSED | CLOSED | OPEN |
| 3RD | OPEN | OPEN | OPEN | CLOSED | CLOSED |
| 4TH | OPEN | OPEN | CLOSED | OPEN | CLOSED |
| 5TH | OPEN | CLOSED | OPEN | OPEN | CLOSED |
| *L/R is closed if output speed is below 100 rpm in Drive and Manual 2. L/R is closed in Manual 1. | |||||
| **May be open when rolling in Neutral or at low oil temperatures. | |||||
Diagnostic Test
1. DETERMINE IF RELATED TCM POWER INPUT DTCS ARE PRESENTWith the scan tool, read Transmission DTCs.
Are there any TCM Power Input DTCs present also?
Yes
- Refer to the Transmission category and perform the appropriate symptom.
No
- Go To2
2. DTC DATA SHOW CURRENT DTC
With the scan tool, check the DTC EVENT DATA.
Does the DTC EVENT DATA show data for DTC P0988?
Yes
- Go To3
No
- Refer to the Transmission category and perform the appropriate symptom shown in the DTC EVENT DATA.
3. MULTIPLE DTCS PRESENT
With the scan tool, check for other transmission DTC's.
Are there two or more related Pressure Switch Sense DTCs present in addition to P0988?
Yes
- Go To4
No
- Go To7
4. RELATED DTC PRESENT
With the scan tool, check the DTC EVENT DATA for P0988.
NOTE: Make sure to record all DTC EVENT DATA stored in the scan tool for future reference in this test procedure.
Do all the pressure switches read CLOSED in the DTC EVENT DATA for P0988?
Yes
- Refer to Transmission category and perform diagnostics for the DTC P0888.
No
- Go To 5
5. DTC EVENT DATA READ OPEN
In the DTC EVENT DATA recorded earlier, read the state of all pressure switches.
Do all the pressure switches read OPEN?
Yes
- Go To 6
No
- Go To 7
6. LOW LINE PRESSURE
In the DTC EVENT DATA recorded earlier, compare the Line Pressure and the Desired Line Pressure.
Is the Line Pressure less than 40 psi, and significantly below the Desired Line Pressure?
Yes
- Repair as necessary to correct low line pressure. Check fluid level and adjust as necessary. If fluid level is OK, check the Primary Oil Filter seal for a split, crack, or improperly installed. If the filter and seal are OK, check the Main Regulator Valve in the Oil Pump. Refer to the Service Information for the above procedures.
- Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - 45RFE/545RFE - STANDARD PROCEDURE)
No
- Replace the Transmission Solenoid/TRS Assembly per the Service Information.
- Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - 45RFE/545RFE - STANDARD PROCEDURE)
7. DTC P0871 ALSO PRESENT
With the scan tool, check Transmission DTCs.
Is the DTC P0871 also present?
Yes
- Refer to the Transmission category and perform the appropriate symptom.
No
- Go To 8
8. EATX DTC EVENT DATA READ PARK REVERSE OR NEUTRAL
With the scan tool, check the DTC EVENT DATA for P0988.
NOTE: Make sure to record all DTC EVENT DATA stored in the scan tool for future reference in this test procedure.
Does the DTC EVENT DATA show the DTC set in Park, Neutral, or Reverse for P0988?
Yes
- Go To 13
No
- Go To 9
9. EATX DTC EVENT DATA READ CLOSED
With the scan tool, check the DTC EVENT DATA for P0988.
NOTE: Make sure to record all DTC EVENT DATA stored in the scan tool for future reference in this test procedure.
Does the DTC EVENT DATA show the 4C Pressure Switch reading CLOSED?
Yes
- Go To 11
No
- Go To 10
10. PRIMARY OIL FILTER SEAL
In the DTC EVENT DATA recorded earlier, compare the Line Pressure and the Desired Line Pressure.
Is the Line Pressure less than 40 psi, and significantly below the Desired Line Pressure?
Yes
- Repair as necessary to correct low line pressure. Check fluid level and adjust as necessary. If fluid level is OK, check the Primary Oil Filter seal for a split, crack, or improperly installed. If the filter and seal are OK, check the Main Regulator Valve in the Oil Pump. Refer to the Service Information for the above procedures.
- Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - 45RFE/545RFE - STANDARD PROCEDURE)
No
- Go To 15
11. PCM AND WIRING
Turn the ignition off to the lock position.
Remove the Starter Relay.
CAUTION: Removal of the Starter Relay will prevent the vehicle from being started in gear.
WARNING: The Starter Relay must be removed from the PDC. Failure to do so can result in personal injury or death.
NOTE: Failure to remove the Starter Relay can cause a Transmission - No Response condition.
Install the Transmission Simulator, Miller tool #8333.
Ignition on, engine not running.
With the Transmission Simulator, turn the Pressure Switch selector switch to the 4C position.
With the scan tool, monitor the 4C Pressure Switch while pressing the Pressure Switch test button on the Transmission Simulator.
Did the state of the 4C Pressure Switch change while pressing the Pressure Switch Test button?
Yes
- Go To 12
No
- Go To 13
12. TRANSMISSION SOLENOID/TRS ASSEMBLY
Using the schematics as a guide, inspect the wiring and connectors specific to this circuit.
Wiggle the wires while checking for shorted and open circuits.
Where there any problems found?
Yes
- Repair as necessary.
- Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - 45RFE/545RFE - STANDARD PROCEDURE)
No
- Replace the Transmission Solenoid/TRS Assembly per the Service Information.
- Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - 45RFE/545RFE - STANDARD PROCEDURE)
13. (T48) 4C PRESSURE SWITCH SENSE CIRCUIT OPEN
Turn the ignition off to the lock position.
Disconnect the Transmission Simulator, Miller tool #8333.
Disconnect the PCM C4 harness connector.
Connect Miller tool #8815 to the PCM C4 harness connector.
CAUTION: Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller tool #8815 to perform diagnosis.
Measure the resistance of the (T48) 4C Pressure Switch Sense circuit from the appropriate terminal of Miller tool #8815 to the Transmission Solenoid/TRS Assembly harness connector.
Is the resistance above 5.0 ohms?
Yes
- Repair the (T48) 4C Pressure Switch Sense circuit for an open.
- Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - 45RFE/545RFE - STANDARD PROCEDURE)
No
- Go To 14
14. (T48) 4C PRESSURE SWITCH SENSE CIRCUIT SHORT TO GROUND
Measure the resistance between ground and the (T48) 4C Pressure Switch Sense circuit.
Is the resistance below 5.0 ohms?
Yes
- Repair the (T48) 4C Pressure Switch Sense circuit for a short to ground.
- Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - 45RFE/545RFE - STANDARD PROCEDURE)
No
- Replace the Powertrain Control Module per the Service Information. With the scan tool, perform the QUICK LEARN procedure.
- Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - 45RFE/545RFE - STANDARD PROCEDURE)
15. #5 AND/OR #7 CHECK BALL CUT OR DAMAGED
Turn the Ignition off to the lock position.
Remove the Valve Body Assembly per the Service Information.
Inspect the #5 check ball for any cuts or damage.
Inspect the 4C accumulator piston and seals and also the 4C tower seal on top of the valve body. Refer to the Service Information.
Where there any problems found?
Yes
- Repair as necessary. Check for excessive clutch debris in the transmission oil pan. If excessive clutch debris is present, repair 4C clutch as necessary. Refer to the Service Information for proper repair procedures.
- Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - 45RFE/545RFE - STANDARD PROCEDURE)
No
- Go To 16
16. EXCESSIVE FLUID LEAKAGE WITH 4C CLUTCH CIRCUIT
Air check the 4C Clutch hydraulic circuit. Refer to the Service Information.
NOTE: This hydraulic clutch circuit contains a small bleed orifice. Small leakage is considered normal.
Was there excessive air leakage in the 4C Clutch hydraulic circuit?
Yes
- Repair as necessary. Refer to the Service Information.
- Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - 45RFE/545RFE - STANDARD PROCEDURE)
No
- Replace the Transmission Solenoid/TRS Assembly per the Service Information.
- Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - 45RFE/545RFE - STANDARD PROCEDURE)