P0988-4C PRESSURE SWITCH RATIONALITYFor a complete wiring diagram Refer to Section 8WTheory of OperationThe 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 CausesRELATED DTCS PRESENTDTC P0871 ALSO PRESENTLOSS OF 12-VOLT FEED(T48) 4C PRESSURE SWITCH SENSE CIRCUIT OPEN(T48) 4C PRESSURE SWITCH SENSE CIRCUIT SHORT TO GROUNDEXCESSIVE FLUID LEAKAGE WITH 4C CLUTCH CIRCUITNO. 5 CHECK BALL CUT OR DAMAGEDLOW LINE PRESSURETRANSMISSION SOLENOID/TRS ASSEMBLYPOWERTRAIN CONTROL MODULEWIRING AND CONNECTORS
Always perform the 45RFE/545RFE Pre-Diagnostic Troubleshooting Procedure before proceeding. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC
- 45RFE/545RFE - STANDARD PROCEDURE)
GEARL/R2C4CUDODREVERSEOPENOPENOPENOPENOPENP/NCLOSED**OPENOPENOPENOPEN1STCLOSED*OPENOPENCLOSEDOPEN2NDOPENCLOSEDOPENCLOSEDOPEN2nd PRIMEOPENOPENCLOSEDCLOSEDOPEN3THOPENOPENOPENCLOSEDCLOSED4THOPENOPENCLOSEDOPENCLOSED5THOPENCLOSEDOPENOPENCLOSED*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 Test1.CHECK FOR OTHER DTCSWith the scan tool, check DTCs.Are there any TCM Power Input DTCs or TIPM TCM Power Control Circuit present?YesRefer to the Transmission category and perform the appropriate symptom.NoGo To22.DTC DATA SHOW CURRENT DTCWith the scan tool, read the DTC EVENT DATA.Does the DTC EVENT DATA show data for DTC P0988?YesGo To3NoRefer to the Transmission category and perform the appropriate symptom identified in the DTC EVENT DATA.3.CHECK IF MULTIPLE DTCS ARE PRESENTWith the scan tool, check DTCs.Are there two or more related Pressure Switch Sense DTCs present in addition to P0988?YesGo To4NoGo To74.RELATED DTC PRESENTWith the scan tool, read the DTC EVENT DATA for P0988.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?YesRefer to Transmission category and perform diagnostics for the DTC P0882.NoGo To 55.CHECK IF THE PRESSURE SWITCHES READ OPENIn the DTC EVENT DATA recorded earlier, read the state the state of all pressure switches.Do all the pressure switches read OPEN?YesGo To 6NoGo To 76.CHECK FOR LOW LINE PRESSUREIn 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?YesRepair 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)NoReplace 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.CHECK IF THE DTC P0871 ALSO SETWith the scan tool, check DTCs.Is the DTC P0871 also present?YesRefer to the Transmission category and perform the diagnostic procedure for P0871.NoGo To 88.CHECK IF THE DTC SET IN PARK, REVERSE OR NEUTRALWith the scan tool, read the DTC EVENT DATA for P0988. 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?YesGo To 13NoGo To 99.CHECK IF THE DTC EVENT DATA READS CLOSEDWith the scan tool, read the DTC EVENT DATA for P0988.Does the DTC EVENT DATA show the 4C Pressure Switch reading CLOSED?YesGo To 11NoGo To 1010.CHECK THE PRIMARY OIL FILTER SEALIn 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?YesRepair 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)NoGo To 1511.CHECK THE PCM AND WIRINGTurn the ignition off to the lock position.Remove the Ignition Switch Feed fuse from the TIPM.Removal of the Ignition Switch Feed fuse from the TIPM will prevent the vehicle from being started in gear. 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?YesGo To 12NoGo To 1312.CHECK THE TRANSMISSION SOLENOID/TRS ASSEMBLYUsing 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?YesRepair as necessary.Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - 45RFE/545RFE - STANDARD PROCEDURE)NoReplace 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.CHECK THE (T48) 4C PRESSURE SWITCH SENSE CIRCUIT FOR AN OPENTurn 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.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?YesRepair 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)NoGo To 1414.CHECK THE (T48) 4C PRESSURE SWITCH SENSE CIRCUIT FOR A SHORT TO GROUNDMeasure the resistance between ground and the (T48) 4C Pressure Switch Sense circuit.Is the resistance below 5.0 ohms?YesRepair the (T48) 4C Pressure Switch Sense circuit for a short to ground.Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST.NoReplace 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.CHECK IF THE NO. 5 AND/OR NO. 7 CHECK BALL IS CUT OR DAMAGEDTurn the Ignition off to the lock position.Remove the Valve Body Assembly per the Service Information.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. Refer to the Service Information.Where there any problems found?YesRepair 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)NoGo To 1616.CHECK FOR EXCESSIVE LEAKAGE WITHIN THE 4C CLUTCH CIRCUITAir check the 4C Clutch hydraulic circuit. Refer to the Service Information.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?YesRepair as necessary. Refer to the Service Information.Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - 45RFE/545RFE - STANDARD PROCEDURE)NoReplace 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)