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.
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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 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
With the scan tool, check for other Transmission DTCs.
Is the DTC P0944 present also?
Yes
-
Refer to the Transmission category and perform the appropriate diagnostic procedure.
No
2.
CHECK FOR RELATED TRANSMISSION DTCS
With the scan tool, read Transmission DTCs.
Are any of the DTCs P0732, P0734 and/or P0846 present also?
Yes
No
3.
CHECK TO SEE IF DTC P0870 IS CURRENT
With the scan tool, view DTCs.
Is the status Active for this DTC or is the STARTS SINCE SET counter 2 or less?
Yes
No
4.
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 and the Electronic Transmission Adapter kit.
Ignition on, engine not running.
With the Transmission Simulator, turn the Pressure Switch selector switch to OD.
With the scan tool, monitor the UD Pressure Switch state while pressing the Pressure Switch Test button on the Transmission Simulator.
Wiggle the wires leading to the PCM while pressing and holding the Pressure Switch Test button.
Did the OD Pressure Switch state change to closed and remain closed while wiggling the wires?
Yes
No
5.
(T9) OD PRESSURE SWITCH SENSE CIRCUIT OPEN
Turn the ignition off to the lock position.
Disconnect the PCM C4 harness connector.
Disconnect the Transmission Solenoid/Pressure Switch Assembly harness connector.
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
tool #8815 to perform diagnosis.
Measure the resistance of the (T9) OD Pressure Switch Sense circuit between the Transmission Solenoid/Pressure Switch Assembly harness connector and the appropriate terminal of Miller tool
#8815.
Is the resistance above 5.0 ohms?
Yes
No
6.
(T9) OD PRESSURE SWITCH SENSE CIRCUIT SHORT TO GROUND
Measure the resistance between ground and the (T9) OD Pressure Switch Sense circuit.
Is the resistance below 5.0 ohms?
Yes
No
7.
(T9) OD PRESSURE SWITCH SENSE CIRCUIT SHORT TO VOLTAGE
Ignition on, engine not running.
With the scan tool under TIPM, actuate the Transmission.
Measure the voltage of the (T9) OD Pressure Switch Sense circuit.
Is the voltage above 0.5 volts?
Yes
No
8.
(T16) TRANSMISSION CONTROL OUTPUT CIRCUIT OPEN
With the scan tool under TIPM, actuate the Transmission.
Using a 12-volt test light connected to ground, check (T16) Transmission Control Output circuit in the Transmission Solenoid/Pressure Switch Assembly harness connector.
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
The conditions necessary to set the 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 shorted and open circuits.
With the scan tool, check the DTC EVENT DATA to help identify the conditions in which the DTC was set.
Were there any problems found?
Yes
No