P0845

P0845-2/4 HYDRAULIC PRESSURE TEST





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


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 verify that the correct pressure switch closes. If the pressure switch does not close 2 times the DTC sets







Always perform the 42RLE Pre-Diagnostic Troubleshooting procedure before proceeding. 42RLE - Pre-Diagnostic Troubleshooting 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 Transmission and Drivetrain and perform the appropriate test.

No

- Go To 2


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

- Replace the Transmission Solenoid/Pressure Switch Assembly.
- Perform 42RLE TRANSMISSION VERIFICATION TEST. 42RLE Transmission Verification Test

No

- Go To 3


3. CHECK TO SEE IF DTC P0845 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

- Go To 4

No

- Go To 9


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 2/4.

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 2/4 Pressure Switch state change to closed and remain closed while wiggling the wires?

Yes

- Disassemble and inspect the Valve Body and repair or replace as necessary. If no problems are found in the Valve Body, replace the Transmission Solenoid/Pressure Switch Assembly.
- Perform 42RLE TRANSMISSION VERIFICATION TEST. 42RLE Transmission Verification Test

No

- Go To 5


5. (T47) 2/4 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.


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 (T47) 2/4 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

- Repair the (T47) 2/4 Pressure Switch Sense circuit for an open.
- Perform 42RLE TRANSMISSION VERIFICATION TEST. 42RLE Transmission Verification Test

No

- Go To 6


6. (T47) 2/4 PRESSURE SWITCH SENSE CIRCUIT SHORT TO GROUND





Measure the resistance between ground and the (T47) 2/4 Pressure Switch Sense circuit.

Is the resistance below 5.0 ohms?

Yes

- Repair the (T47) 2/4 Pressure Switch Sense circuit for a short to ground.
- Perform 42RLE TRANSMISSION VERIFICATION TEST. 42RLE Transmission Verification Test

No

- Go To 7


7. (T47) 2/4 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 (T47) 2/4 Pressure Switch Sense circuit.

Is the voltage above 0.5 volts?

Yes

- Repair the (T47) 2/4 Pressure Switch Sense circuit for a short to voltage.
- Perform 42RLE TRANSMISSION VERIFICATION TEST. 42RLE Transmission Verification Test

No

- Go To 8


8. 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 Relay 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. With the scan tool, perform QUICK LEARN.
- Perform 42RLE TRANSMISSION VERIFICATION TEST. 42RLE Transmission Verification Test

No

- Repair the Transmission Control Relay Output circuit for an open or high resistance. If the fuse is open make sure to check for a short to ground.
- Perform 42RLE TRANSMISSION VERIFICATION TEST. 42RLE Transmission Verification Test


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

- Repair as necessary.
- Perform 42RLE TRANSMISSION VERIFICATION TEST. 42RLE Transmission Verification Test

No

- Test Complete.