P0870-OD HYDRAULIC PRESSURE TEST





For a complete wiring diagram Refer to Section 8W.

Theory of Operation


Pressure switches are normally off or open (no pressure applied) and read high (+12 volts). When an element is applied, the corresponding pressure switch closes to ground (0 volts) or turns on. The controller tests the OD and 2/4 pressure switches when they are off (when the corresponding friction element is not applied) by briefly applying the OD and 2/4 elements which will cause the corresponding pressure switch to close. The test verifies that the switches are operational and that the switch will close when the corresponding element is applied. If a switch fails to respond, it is re-tested. The MIL illuminates and the transmission system defaults to Limp-in mode.


  • 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 greater than 1000 RPM, the PCM momentarily turns on element pressure to the clutch circuits that don't have pressure to identify the correct pressure switch closes. If the pressure switch does not close 2 times the DTC sets.


Possible Causes
  
LOSS OF PRIME P0944 PRESENT
  
(T16) TRANSMISSION CONTROL RELAY OUTPUT CIRCUIT OPEN
  
(T9) OD PRESSURE SWITCH SENSE CIRCUIT OPEN
  
(T9) OD PRESSURE SWITCH CIRCUIT SHORT TO GROUND
  
(T9) OD PRESSURE SWITCH SENSE CIRCUIT SHORT TO VOLTAGE
  
TRANSMISSION SOLENOID/PRESSURE SWITCH ASSEMBLY
  
INTERNAL TRANSMISSION
  
POWERTRAIN CONTROL MODULE
  

Always perform the 42RLE Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - 42RLE - STANDARD PROCEDURE)



Diagnostic Test

1.CHECKING FOR LOSS OF PRIME DTC



Is the DTC P0944 present also?

Yes
  • Refer to the Transmission category and perform the appropriate diagnostic procedure.


No
  • Go To 2

2.CHECK FOR RELATED TRANSMISSION DTCS



Are any of the DTCs P0732, P0734 and/or P0846 present also?

Yes


No
  • Go To 3

3.CHECK TO SEE IF DTC P0870 IS CURRENT



Is the status Active for this DTC or is the STARTS SINCE SET counter 2 or less?

Yes
  • Go To 4


No
  • Go To 9

4.PCM AND WIRING



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 can result in personal injury or death.


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








Did the OD Pressure Switch state change to closed and remain closed while wiggling the wires?

Yes


No
  • Go To 5

5.(T9) OD PRESSURE SWITCH SENSE CIRCUIT OPEN






NOTE: Check connectors - Clean/repair as necessary.


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 Special Tool #8815 to perform diagnosis.




Is the resistance above 5.0 ohms?

Yes


No
  • Go To 6

6.(T9) OD PRESSURE SWITCH SENSE CIRCUIT SHORT TO GROUND





Is the resistance below 5.0 ohms?

Yes


No
  • Go To 7

7.(T9) OD PRESSURE SWITCH SENSE CIRCUIT SHORT TO VOLTAGE




NOTE: Check connectors - Clean/repair as necessary.






Is the voltage above 0.5 volts?

Yes


No
  • Go To 8

8.(T16) TRANSMISSION CONTROL RELAY OUTPUT CIRCUIT OPEN



NOTE: The jumper wire must still be in place.



NOTE: The test light must illuminate brightly. Compare the brightness to that of a direct connection to the battery.



Does the test light illuminate brightly?

Yes
  • 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 per the Service Information. With the scan tool, perform QUICK LEARN
  • Perform 42RLE TRANSMISSION VERIFICATION TEST. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - 42RLE - STANDARD PROCEDURE)


No

9.INTERMITTENT WIRING AND CONNECTORS






Were there any problems found?

Yes


No
  • Test Complete.