68RFE Automatic Transmission

P0988-4C PRESSURE SWITCH RATIONALITY





For a complete wiring diagram refer to Diagrams/Electrical. Electrical Diagrams


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. 68RFE Pre-Diagnostic Troubleshooting Procedure








Diagnostic Test


1. CHECK FOR RELATED DTCS

With the scan tool, check DTCs.

Are there any TIPM TCM Power Control Circuit or TCM Power Input DTCs present?

Yes

- Refer to the Transmission category and perform the appropriate symptom.

No

- Go To 2



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 identified in the DTC EVENT DATA.



3. CHECK IF MULTIPLE DTCS ARE PRESENT

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 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 P0882. P0882

No

- Go To 5



5. CHECK IF THE PRESSURE SWITCHES 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. CHECK FOR 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.
- Perform 68RFE TRANSMISSION VERIFICATION TEST. 68RFE Transmission Verification Test

No

- Replace the Transmission Solenoid/TRS Assembly.
- Perform 68RFE TRANSMISSION VERIFICATION TEST. 68RFE Transmission Verification Test



7. CHECK IF THE DTC P0871 ALSO SET

With the scan tool, check Transmission DTCs.

Is the DTC P0871 also present?

Yes

- Refer to the Transmission category and perform the diagnostic procedure for P0871. P0871

No

- Go To 8



8. CHECK IF THE DTC SET IN 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 P0988 set in Park, Neutral, or Reverse?

Yes

- Go To 13

No

- Go To 9



9. CHECK IF THE DTC EVENT DATA READS CLOSED

With the scan tool, check the DTC EVENT DATA for P0988.

Does the DTC EVENT DATA show the 4C Pressure Switch reading CLOSED?

Yes

- Go To 11

No

- Go To 10



10. CHECK THE 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.
- Perform 68RFE TRANSMISSION VERIFICATION TEST. 68RFE Transmission Verification Test

No

- Go To 15



11. CHECK THE PCM AND WIRING

Turn the ignition off to the lock position.

Remove the Ignition Switch Feed fuse from the TIPM.


CAUTION: Removal of the Ignition Switch Feed fuse from the TIPM will prevent the vehicle from being started in gear.


WARNING: The Ignition Switch Feed fuse must be removed from the TIPM. Failure to do so can result in personal injury or death.

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. CHECK THE 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 68RFE TRANSMISSION VERIFICATION TEST. 68RFE Transmission Verification Test

No

- Replace the Transmission Solenoid/TRS Assembly.
- Perform 68RFE TRANSMISSION VERIFICATION TEST. 68RFE Transmission Verification Test



13. CHECK THE (T48) 4C PRESSURE SWITCH SENSE CIRCUIT FOR AN 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 between the Transmission Solenoid/TRS Assembly harness connector and the appropriate terminal of Miller tool #8815.

Is the resistance above 5.0 ohms?

Yes

- Repair the (T48) 4C Pressure Switch Sense circuit for an open.
- Perform 68RFE TRANSMISSION VERIFICATION TEST. 68RFE Transmission Verification Test

No

- Go To 14



14. CHECK THE (T48) 4C PRESSURE SWITCH SENSE CIRCUIT FOR A 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 68RFE TRANSMISSION VERIFICATION TEST. 68RFE Transmission Verification Test

No

- Replace the Powertrain Control Module. With the scan tool, perform the QUICK LEARN procedure.
- Perform 68RFE TRANSMISSION VERIFICATION TEST. 68RFE Transmission Verification Test



15. CHECK IF THE #5 AND/OR #7 CHECK BALL IS CUT OR DAMAGED

Turn the Ignition off to the lock position.

Remove the Valve Body Assembly.

Inspect the #5 and #7 check balls for any cuts or damage.

Inspect the 4C accumulator piston and seals and also the 4C tower seal on top of the valve body.

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.
- Perform 68RFE TRANSMISSION VERIFICATION TEST. 68RFE Transmission Verification Test

No

- Go To 16



16. CHECK FOR EXCESSIVE LEAKAGE WITHIN THE 4C CLUTCH CIRCUIT

Air check the 4C Clutch hydraulic circuit.


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.
- Perform 68RFE TRANSMISSION VERIFICATION TEST. 68RFE Transmission Verification Test

No

- Replace the Transmission Solenoid/TRS Assembly.
- Perform 68RFE TRANSMISSION VERIFICATION TEST. 68RFE Transmission Verification Test