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P0988






P0988-4C PRESSURE SWITCH RATIONALITY





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

Theory of Operation

The Transmission system uses five pressure switches to monitor the fluid pressure in the LR, 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. CHECK FOR RELATED DTCS
1. With the scan tool, check for other transmission DTCs.

Are there any Transmission Control Relay or TCM Power Input DTCs present?

Yes

- Testing and Inspection Perform the appropriate diagnostic procedure.
- Perform the 545RFE TRANSMISSION VERIFICATION TEST. Transmission Verification Test

No

- Go To 2

2. CHECK IF THE DTC DATA SHOWS CURRENT DTC
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 Inspection Perform the appropriate diagnostic procedure shown in the Event Data.

3. CHECK IF MULTIPLE DTCS ARE PRESENT
1. With the scan tool, check for other transmission DTCs.

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

Yes

- Go To 4

No

- Go To 7

4. CHECK IF A RELATED DTC IS 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

- P0882 Perform diagnostics for the DTC P0882.

No

- Go To 5

5. CHECK IF THE Event Data READS OPEN
1. In the 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. CHECK FOR LOW LINE PRESSURE
1. In the 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 the 545RFE TRANSMISSION VERIFICATION TEST. Transmission Verification Test

No

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

7. CHECK IF THE DTC P0871 IS ALSO PRESENT
1. With the scan tool, check Transmission DTCs.

Is the DTC P0871 also present?

Yes

- Testing and Inspection Perform the appropriate diagnostic procedure.

No

- Go To 8

8. CHECK IF THE Event Data READS IN PARK, REVERSE OR NEUTRAL
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.

Does the Event Data show the DTC set in Park, Reverse or Neutral for P0988?

Yes

- Go To 13

No

- Go To 9

9. CHECK IF THE Event Data READS CLOSED
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.

Does the Event Data show the 4C Pressure Switch reading CLOSED?

Yes

- Go To 11

No

- Go To 10

10. CHECK THE PRIMARY OIL FILTER SEAL
1. In the 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 the 545RFE TRANSMISSION VERIFICATION TEST. Transmission Verification Test

No

- Go To 15

11. CHECK THE PCM AND WIRING WITH THE TRANSMISSION SIMULATOR
1. Turn the ignition off to the lock position.
2. Remove the Starter Relay.

NOTE: Removal of the Starter Relay is to prevent a Transmission, NO RESPONSE, condition and disable the starter.

3. Install the Transmission Simulator 8333.

NOTE: Check connectors - Clean/repair as necessary.

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. CHECK THE WIRING AND CONNECTORS
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. Transmission Verification Test

No

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

13. CHECK THE (T48) 4C PRESSURE SWITCH SENSE 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.

NOTE: Check connectors - Clean/repair as necessary.

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 Switch Sense circuit from the appropriate terminal of the PCM Pinout Box 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 the 545RFE TRANSMISSION VERIFICATION TEST. Transmission Verification Test

No

- Go To 14

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




1. 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 the 545RFE TRANSMISSION VERIFICATION TEST. Transmission Verification Test

No

- Replace the Powertrain Control Module. With the scan tool, perform the Quick Learn procedure. Quick Learn Procedure
- Perform the 545RFE TRANSMISSION VERIFICATION TEST. Transmission Verification Test

15. CHECK IT THE #5 CHECK BALL IS CUT OR DAMAGED
1. Turn the Ignition off to the lock position.
2. Remove the Valve Body Assembly.
3. Inspect the #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. Transmission Verification Test

No

- Go To 16

16. CHECK FOR EXCESSIVE FLUID LEAKAGE IN THE 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. Transmission Verification Test

No

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