HYDRAULIC PRESSURE SWITCH CIRCUIT

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Darleen Beasley
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1 Symptom: P1787-OD HYDRAULIC PRESSURE SWITCH CIRCUIT When Monitored and Set Condition: P1787-OD HYDRAULIC PRESSURE SWITCH CIRCUIT When Monitored: In any forward gear with engine speed above 1000 RPM shortly after a shift and every minute thereafter. Set Condition: After a shift into a forward gear, with engine speed > 1000 RPM, the TCM momentarily turns on element pressure to the clutch ckts that don t have pressure to identify the correct pressure sw closes. If the pressure sw does not close 2 times the code sets POSSIBLE CAUSES TRANSMISSION RELAY OUTPUT CIRCUIT OPEN RELATED LINE PRESSURE DTC S PRESENT EXCESSIVE DEBRIS IN OIL PAN INTERMITTENT WIRING & CONNECTORS CONDITIONS INTERNAL TRANSMISSION PROBLEM - OD PRESSURE TEST RELATED SPEED RATIO AND/OR PRESSURE SWITCH DTC S PRESENT OD PRESSURE SWITCH SENSE CIRCUIT OPEN OD PRESSURE SWITCH SENSE CIRCUIT SHORT TO GROUND LINE PRESSURE SENSOR DEFECTIVE POOR LPS CONNECTION 5-VOLT SUPPLY CIRCUIT OPEN 5-VOLT SUPPLY CIRCUIT SHORT TO GROUND OD PRESSURE SWITCH SENSE CIRCUIT SHORT TO VOLTAGE TCM DEFECTIVE TCM DEFECTIVE NO 5 VOLTS LOW LP INCORRECT FLUID LEVEL TRANSMISSION RELAY OUTPUT CIRCUIT OPEN 1 With the DRB, check for other transmission DTC s Are there any line pressure related DTC s present? (P-1720, 1721, 1722, 1724, or 1791) Yes Refer to symptom list and perform test for loss of prime or line pressure DTC s. No Go To 2 149

2 2 With the DRB, check for other transmission DTC s Is DTC P-0733(3rd ratio) and/or P-1781(OD pressure switch) present also? Yes Replace the Transmission or Solenoid/TRS assembly per current warranty policy. No Go To 3 3 Start engine. Warm transmission to 180 degrees. Firmly apply brakes. While monitoring transmission line pressure with the DRB, move the shift lever to each gear position and record the line pressure reading. Allow the pressure to stabilize for at least 5 seconds in each range. Did the line pressure remain at a steady value between 85 and 95 PSI during the procedure? Yes Go To 4 No Go To 10 4 Turn ignition on. Engine off. While observing Actual Line Pressure with the DRB, firmly push the line pressure sensor connector towards the trans. Did the Actual Line Pressure change to about 30 when the sensor connector was pushed? Yes Disconnect and properly reconnect the Line Pressure Sensor connector. Inspect terminals and repair as necessary. No Go To 5 5 Install Transmission simulator (Miller tool #8333) and the DRBIII. With the DRB, monitor the Line Pressure during the following step. Using the Transmission Simulator, set the rotary knob to each of the 3 line pressure positions. Note: all three DRB line pressure sensor voltage readings should be within 0.25 volts of the voltage reading specified on simulator. Did the Line Pressure remain steady while changing the knob position. Yes Go To 6 No Go To 9 6 Turn ignition switch to the lock position Disconnect thetransmission Control Module (TCM). (See TRANSMISSION CON- Disconnect the Line Pressure Sensor connector. Measure the resistance of the 5-Volt Supply circuit from the Line Pressure Sensor connector to the TCM connector. Is the resistance above 5.0 ohms? Yes open 5-Volt Supply circuit No Go To 7 150

3 7 Turn ignition switch to the lock position. Disconnect thetransmission Control Module (TCM). (See TRANSMISSION CON- Disconnect the Line Pressure Sensor connector. Measure the resistance between the 5-Volt Supply circuit and ground. Is the resistance Below 5.0 ohms? Yes 5-Volt Supply circuit short to ground. No Go To 8 8 All other possible causes must be eliminated prior to TCM replacement. If there are no potential causes remaining, The TCM is assumed to be defective. Replace the TCM. 9 The controller and wiring are functioning normally. The Sensor must be the problem. The TCM and wiring are functioning normally. Replace the Line Pressure Sensor. Replace the Line Pressure Sensor. 10 Perform a visual inspection of all connectors, wiring, and cooler connections before proceeding. as necessary. Check the transmission fluid level per service instructions. Adjust if necessary. With the DRBIII, Check the STARTS SINCE SET counter. Note: This counter only applies to the last code set. Is the STARTS SINCE SET counter 2 or less? Yes Go To 11 No Go To Install Transmission simulator (Miller tool #8333) Place pressure switch selector on OD and observe DRB screen while pressing pressure switch test button. Wiggle the wires leading to the TCM while pressing the button. Did the OD pressure switch state change to closed and remain closed while wiggling the wires? Yes Go To 12 No Go To

4 12 The transmission must be at operating temperature prior to checking fluid level. Adjusting fluid level on a cold transmission will result in an overfilled transmission. Check the transmission fluid level per the service manual procedure. Note: The transmission must be hot when checking oil level. When the temperature is below 50 degrees F. (100 C), it is possible that no oil will show on the dipstick, even though the transmission has an adequate fill level when warm. Is the fluid level OK? Yes Go To 13 No Adjust fluid level. cause of incorrect fluid level. 13 Remove and inspect transmission oil pan per service instructions. Does it contain excessive debris or contamination? Yes cause of excessive debris in transmission oil pan. No Go To The transmission has an internal problem and must be replaced or repaired. If the transmission is to be repaired, disassemble and inspect the Valve Body per service instructions and repair or replace as necessary. If no problems are found in the valve body, replace the solenoid/trs assembly. Replace or repair the transmission as necessary. Replace transmission or repair internal transmission problem as required per current warranty policy. 15 Turn the ignition switch to the lock position. Disconnect the Transmission Control Module connector. Disconnect the Transmission Solenoid/TRS connector. Measure the resistance between the OD Pressure Switch Sense circuit and ground. Is the resistance below 5.0 ohms? Yes OD Pressure Switch circuit short to ground. No Go To Turn the ignition switch to the lock position. Disconnect the Transmission Control Module connector. Remove the Transmission Control Relay. Connect a jumper wire between the Fused B(+) circuit and the Trans Relay Output circuit in the relay connector. Turn ignition switch on. Measure the voltage of the OD Pressure Switch Sense circuit in the TCM connector. Is the voltage above 3.0 volts? Yes OD Pressure Switch Sense circuit short to voltage. No Go To

5 17 Turn the ignition switch to the lock position. Disconnect the transmission solenoid/trs connector. Remove the Transmission Control relay. Place a jumper wire between the Fused B(+) and Transmission Control Relay Output circuits in the Transmission Control Relay connector. Connect the test light clamp to a good ground. Probe the Transmission Relay Output circuit in the solenoid/trs connector with the test light Does the light illuminate brightly? Yes Go To 18 No cause of unlit or dim test light. (Open circuit or high resistance in trans relay output circuit) 18 Turn the ignition switch to the lock position. Disconnect the Transmission Control Module (TCM). (See TRANSMISSION CON- Disconnect the transmission solenoid /TRS connector Measure the resistance of the OD Pressure Switch Sense circuit from the TCM connector to the solenoid/trs connector. Is the resistance above 5.0 ohms? Yes the open OD Pressure Switch Sense circuit. No Go To All other possible causes must be eliminated prior to TCM replacement. If there are no potential causes remaining, The TCM is assumed to be defective. Replace the TCM. 20 The conditions necessary to set this DTC are not present at this time.using the schematics as a guide, inspect the wiring and connectors specific to this circuit. Wiggle the wires while checking for shorts and open circuits. Were any problems found? Yes defective wiring and/or connector as necessary. No Test Complete. 153

HYDRAULIC PRESSURE SWITCH CIRCUIT

Symptom: P1726-UD HYDRAULIC PRESSURE SWITCH CIRCUIT When Monitored and Set Condition: P1726-UD HYDRAULIC PRESSURE SWITCH CIRCUIT When Monitored: In any forward gear with engine speed above 1000 RPM shortly