P0846
P0846-2/4 PRESSURE SWITCH RATIONALITY
For a complete wiring diagram, refer to: Electrical Diagrams
When Monitored
Whenever the engine is running.
Set Condition
The DTC is set if one of the pressure switches are open or closed at the wrong time in a given gear. If the problem is identified for 3 successive key starts, the transmission will go into Limp-in mode a MIL will turn on after 10 seconds of vehicle operation.
Possible Causes
- RELATED TRANSMISSION RELAY DTC'S PRESENT LOSS OF PRIME DTC PRESENT
- (T47) 2/4 PRESSURE SWITCH SENSE CIRCUIT OPEN
- (T47) 2/4 PRESSURE SWITCH SENSE CIRCUIT SHORT TO GROUND
- (T47) 2/4 PRESSURE SWITCH SENSE CIRCUIT SHORT TO VOLTAGE
- TRANSMISSION SOLENOID/PRESSURE SWITCH ASSEMBLY
- POWERTRAIN CONTROL MODULE
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.
Theory of Operation
The Transmission system uses three pressure switches to monitor the fluid pressure in the LR, 2/4, and OD elements. The pressure switches are continuously monitored for the correct states in each gear. The 2/4 pressure switch monitors the fluid pressure to the 2/4 clutch to confirm proper operation of the 2/4 solenoid. If the 2/4 pressure switch is identified as closed in P or N, the code will immediately be set and normal operation will be allowed for that given key start. If the problem is identified for 3 successive ignition cycles, the transmission will go into Limp-in mode.
PRESSURE SWITCH STATES
Diagnostic Test
1. DETERMINING IF RELATED TRANSMISSION RELAY DTC'S ARE PRESENT
With the scan tool, read Transmission DTC's
Are there any Transmission Control Relay DTC's present also?
Yes >> Refer to the Transmission category and perform the appropriate symptom.
Perform 42RLE TRANSMISSION VERIFICATION TEST - Ver 1. Verification Tests.
No >> Go To 2
2. CHECK FOR LOSS OF PRIME DTC
With the scan tool, check for other Transmission DTC's.
Is the DTC P0944 present also?
Yes >> Refer to the Transmission category and perform the appropriate diagnostic procedure.
Perform 42RLE TRANSMISSION VERIFICATION TEST - Ver 1. Verification Tests.
No >> Go To 3
3. CHECK TO SEE IF P0846 IS CURRENT
With the scan tool, Check the STARTS SINCE SET counter for P0846.
NOTE: This counter only applies to the last DTC set.
Is the STARTS SINCE SET counter 2 or less?
Yes >> Go To 4
No >> Go To 10
4. PCM AND WIRING
Turn the ignition off to the lock position.
Remove the Starter Relay.
CAUTION: Removal of the Starter Relay is to prevent a Transmission, NO RESPONSE, condition and disable the starter.
Install the Transmission Simulator, Miller tool #8333 and the Electronic Transmission Adapter kit 8333-1A.
NOTE: Check connectors - Clean/repair as necessary.
Ignition on, engine not running. With the Transmission Simulator, turn the Pressure Switch selector 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.
Did the 2/4 Pressure Switch state change?
Yes >> Go To 8
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.
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.
Measure the resistance of the (T47) 2APressure Switch Sense circuit from the appropriate terminal of special tool #8815 to the Transmission Solenoid/Pressure Switch Assembly harness connector.
Is the resistance above 5.0 ohms?
Yes >> Repair the (T47) 2APressure Switch Sense circuit for an open.
Perform 42RLE TRANSMISSION VERIFICATION TEST - Ver 1. Verification Tests.
No >> Go To 6
6. (T47) 2/4 PRESSURE SWITCH SENSE CIRCUIT SHORT TO GROUND
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.
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 - Ver 1. Verification Tests.
No >> Go To 7
7. (T47) 2/4 PRESSURE SWITCH SENSE CIRCUIT SHORT TO VOLTAGE
Turn the ignition off to the lock position.
Disconnect the PCM C4 harness connector.
Disconnect the Transmission Solenoid/Pressure Switch Assembly harness connector.
Remove the Transmission Control Relay
NOTE: Check connectors - Clean/repair as necessary.
Connect a jumper wire between the (Internal) Fused B+ circuit and (T16) Transmission Control Relay Output circuit.
Ignition on, engine not running.
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 - Ver 1. Verification Tests.
No >> Go To 9
8. 2/4 PRESSURE SWITCH
If there are no possible causes remaining, view repair.
Repair
Replace the Transmission Solenoid/Pressure Switch Assembly per the Service Information.
Perform 42RLE TRANSMISSION VERIFICATION TEST - Ver 1. Verification Tests.
9. POWERTRAIN CONTROL MODULE
Using the schematics as a guide, inspect the wiring and connectors. Repair as necessary Pay particular attention to all power and ground circuits.
If there are no possible causes remaining, view repair.
Repair
Replace the Powertrain Control Module per the Service Information. With the scan tool perform QUICK LEARN, then program Pinion Factor in the Front Control Module.
Perform 42RLE TRANSMISSION VERIFICATION TEST - Ver 1. Verification Tests.
10. 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 EATX 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 - Ver 1. Verification Tests.
No >> Test Complete.