P0988

P0988-4C PRESSURE SWITCH RATIONALITY





For a complete wiring diagram, refer to the Wiring Information.

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.





Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Pre-Diagnostic Troubleshooting Procedure.






1. DETERMINE IF RELATED TCM POWER INPUT DTCS ARE PRESENT
1. With the scan tool, read DTCs.

Are there any TCM Power Input DTCs present also?

Yes

- Testing and InspectionPerform the appropriate diagnostic procedure.

No

- Go To 2

2. CHECK THE EVENT DATA
1. With the scan tool, check the Event Data.

Does the Event Data show data for DTC P0988?

Yes

- Go To 3

No

- Testing and InspectionPerform the appropriate diagnostic procedure.

3. MULTIPLE DTCS PRESENT
1. With the scan tool, read DTCs.

Are there two or more related Pressure Switch DTCs present in addition to P0988?

Yes

- Go To 4

No

- Go To 7

4. RELATED DTC PRESENT
1. With the scan tool, check the Event Data for P0988.

NOTE: Make sure to record all Event Data stored in the scan tool for future reference in this test procedure.

Do all the pressure switches read CLOSED in the Event Data for P0988?

Yes

- Perform diagnostics for the DTC P0882. P0882

No

- Go To 5

5. EVENT DATA READ OPEN

In the Event Data recorded earlier, do all the pressure switches read OPEN?

Yes

- Go To 6

No

- Go To 7

6. LOW LINE PRESSURE

In the Event Data recorded earlier, 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 the 545RFE TRANSMISSION VERIFICATION TEST. . 545RFE Transmission Verification Test

No

- Replace the Transmission Solenoid/TRS Assembly.
- Perform the 545RFE TRANSMISSION VERIFICATION TEST. . 545RFE Transmission Verification Test

7. DTC P0871 ALSO PRESENT
1. With the scan tool, read DTCs.

Is the DTC P0871 also present?

Yes

- Testing and InspectionPerform the appropriate diagnostic procedure.

No

- Go To 8

8. EVENT DATA READ PARK REVERSE OR NEUTRAL

In the Event Data recorded earlier, does the Event Data show the DTC set in Park, Neutral, or Reverse for P0988?

Yes

- Go To 13

No

- Go To 9

9. EVENT DATA READ CLOSED

In the Event Data recorded earlier, does the Event Data show the 4C Pressure Switch reading CLOSED?

Yes

- Go To 11

No

- Go To 10

10. PRIMARY OIL FILTER SEAL

In the Event Data recorded earlier, 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 the 545RFE TRANSMISSION VERIFICATION TEST. . 545RFE Transmission Verification Test

No

- Go To 15

11. CHECK THE PCM AND WIRING USING THE TRANSMISSION SIMULATOR
1. Turn the ignition off to the lock position.
2. 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 may result in possible serious or fatal injury.

NOTE: Failure to remove the Starter Relay can cause a Transmission - No Response condition.

3. Install the Transmission Simulator 8333.
4. Ignition on, engine not running.
5. With the Transmission Simulator, turn the Pressure Switch selector switch to the 4C position.
6. 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
1. Using the schematics as a guide, inspect the wiring and connectors specific to this circuit.
2. Wiggle the wires while checking for shorted and open circuits.

Where there any problems found?

Yes

- Repair as necessary.
- Perform the 545RFE TRANSMISSION VERIFICATION TEST. . 545RFE Transmission Verification Test

No

- Replace the Transmission Solenoid/TRS Assembly.
- Perform the 545RFE TRANSMISSION VERIFICATION TEST. . 545RFE Transmission Verification Test

13. CHECK THE (T48) 4C PRESSURE SIGNAL CIRCUIT FOR AN OPEN




1. Turn the ignition off to the lock position.
2. Disconnect the Transmission Simulator 8333.
3. Disconnect the PCM C4 harness connector.
4. Connect the PCM Pinout Box 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 the PCM Pinout Box 8815 to perform diagnosis.

5. Measure the resistance of the (T48) 4C Pressure Signal circuit between the Transmission Solenoid/TRS Assembly harness connector and the appropriate terminal of the PCM Pinout Box 8815.

Is the resistance above 5.0 Ohms?

Yes

- Repair the (T48) 4C Pressure Signal circuit for an open.
- Perform the 545RFE TRANSMISSION VERIFICATION TEST. . 545RFE Transmission Verification Test

No

- Go To 14

14. CHECK THE (T48) 4C PRESSURE SIGNAL CIRCUIT FOR A SHORT TO GROUND




1. Measure the resistance between ground and the (T48) 4C Pressure Signal circuit.

Is the resistance below 5.0 Ohms?

Yes

- Repair the (T48) 4C Pressure Signal circuit for a short to ground.
- Perform the 545RFE TRANSMISSION VERIFICATION TEST. . 545RFE Transmission Verification Test

No

- Using the schematics as a guide, check the Powertrain Control Module (PCM) terminals for corrosion, damage, or terminal push out. Pay particular attention to all power and ground circuits. If no problems are found, replace and program the PCM. With the scan tool, perform Quick Learn. Quick Learn Procedure
- Perform the 545RFE TRANSMISSION VERIFICATION TEST. . 545RFE Transmission Verification Test

15. NO. 5 CHECK BALL CUT OR DAMAGED
1. Turn the Ignition off to the lock position.
2. Remove the Valve Body Assembly.
3. Inspect the No. 5 check ball for any cuts or damage.
4. 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 the 545RFE TRANSMISSION VERIFICATION TEST. . 545RFE Transmission Verification Test

No

- Go To 16

16. EXCESSIVE FLUID LEAKAGE WITH 4C CLUTCH CIRCUIT
1. 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 the 545RFE TRANSMISSION VERIFICATION TEST. . 545RFE Transmission Verification Test

No

- Replace the Transmission Solenoid/TRS Assembly.
- Perform the 545RFE TRANSMISSION VERIFICATION TEST. . 545RFE Transmission Verification Test