P0845
P0845-2/4 HYDRAULIC PRESSURE TEST
For a complete wiring diagram Consult Diagrams/Electrical.
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 24 pressure switches when they are off (when the corresponding friction element is not applied) by briefly applying the OD and 24 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 40/41TE Pre-Diagnostic Troubleshooting procedure before proceeding. Testing and Inspection
Diagnostic Test
1. CHECK FOR LOSS OF PRIME DTC
With the scan tool, read DTCs.
Is the DTC P0944 present also?
Yes
- Diagnose and repair the DTC(s). P0944
No
- Go to 2
2. CHECK FOR RELATED DTCS
With the scan tool, read DTCs.
Are any of the DTCs P0732, P0734 and/or P0846 present also?
Yes
- Replace the Transmission Solenoid/Pressure Switch Assembly.
- PERFORM 40/41TE VERIFICATION TEST Transmission Verification Test
No
- Go to 3
3. CHECK IF DTC P0845 IS CURRENT
With the scan tool, read DTCs.
Is the status Active or is the Starts Since Set counter 2 or less for this DTC?
Yes
- Go to 4
No
- Go to 9
4. CHECK THE PCM AND WIRING WITH THE TRANSMISSION SIMULATOR
Turn the ignition off to the lock position.
Remove the Starter Relay.
CAUTION: Removal of the Starter Relay will prevent the vehicle from being started in gear.
WARNING: The Starter Relay must be removed. Failure to do so can result in personal injury or death.
Install the Transmission Simulator, Miller tool #8333 and the Electronic Transmission Adapter kit.
NOTE: Check connectors - Clean/repair as necessary.
Ignition on, engine not running.
With the Transmission Simulator, turn the Pressure Switch selector switch to 2/4.
With the scan tool, monitor the 2/4 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 40/41TE VERIFICATION TEST Transmission Verification Test
No
- Go to 5
5. CHECK THE (T47) 2/4 PRESSURE SIGNAL CIRCUIT FOR AN 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 Special Tool #8815 to perform diagnosis.
Measure the resistance of the (T47) 2/4 Pressure Signal circuit between the Transmission Solenoid/Pressure Switch Assembly harness connector and appropriate terminal of Miller tool #8815.
Is the resistance above 5.0 ohms?
Yes
- Repair the (T47) 2/4 Pressure Signal circuit for an open.
- PERFORM 40/41TE VERIFICATION TEST Transmission Verification Test
No
- Go to 6
6. CHECK THE (T47) 2/4 PRESSURE SIGNAL CIRCUIT FOR A SHORT TO GROUND
Measure the resistance between ground and the (T47) 2/4 Pressure Signal circuit.
Is the resistance below 5.0 ohms?
Yes
- Repair the (T47) 2/4 Pressure Signal circuit for a short to ground.
- PERFORM 40/41TE VERIFICATION TEST Transmission Verification Test
No
- Go to 7
7. CHECK THE (T47) 2/4 PRESSURE SIGNAL CIRCUIT FOR A SHORT TO VOLTAGE
Remove the Transmission Control Relay.
Connect a jumper wire between the Fused B(+) circuit and the Transmission Control Output circuit in the Transmission Control Relay connector.
Ignition on, engine not running.
Measure the voltage of the (T47) 2/4 Pressure Signal circuit.
Is the voltage above 0.5 volts?
Yes
- Repair the (T47) 2/4 Pressure Signal circuit for a short to voltage.
- PERFORM 40/41TE VERIFICATION TEST Transmission Verification Test
No
- Go to 8
8. CHECK THE (T16) TRANSMISSION CONTROL OUTPUT CIRCUIT FOR AN OPEN
With jumper wire still connected from the previous step, 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. Check for Service Information Tune-ups or Service Bulletins for any possible causes that may apply. If no problems are found, replace and program the PCM . With the scan tool, perform Quick Learn.
- PERFORM 40/41TE VERIFICATION TEST Transmission Verification Test
No
- Repair the (T16) Transmission Control Output circuit for an open or high resistance. If the fuse is open make sure to check for a short to ground.
- PERFORM 40/41TE VERIFICATION TEST Transmission Verification Test
9. CHECK THE 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 Event Data to help identify the conditions in which the DTC was set.
Were there any problems found?
Yes
- Repair as necessary.
- PERFORM 40/41TE VERIFICATION TEST Transmission Verification Test
No
- Test Complete.