P0868

P0868-LINE PRESSURE LOW





For a complete wiring diagram Consult Diagrams/Electrical

Theory of Operation

Line pressure is measured by the Line Pressure Sensor (LPS) and regulation is achieved by changing the duty cycle of the Pressure Control Solenoid (PCS) controlled by the Transmission Control System. (5% duty cycle = solenoid off = max line pressure, 62% duty cycle = solenoid on = min line pressure). The Transmission Control System calculates the desired line pressure based on inputs from both the engine and transmission.

The Transmission Control System calculates torque input to the transmission and uses it as the primary input to the desired line pressure calculation. This is called Torque Based Line Pressure. In addition, the line pressure is set to a preset level 827 or 931 kPa (120 or 135 psi) during shifts and in Park and Neutral to ensure consistent shift quality. The desired line pressure is continuously being compared to the actual line pressure. If the actual line pressure is consistently lower than the target while driving, the line pressure low DTC P0868 will set.

- When Monitored:
Continuously while driving in a forward gear.

- Set Condition:
The PCM continuously monitors Actual Line Pressure and compares it to Desired Line Pressure. If the Actual Line Pressure is more than 15 psi below Desired Line Pressure for 3.5 seconds continuously, this DTC will set.





Always perform the 45RFE/545RFE Pre-Diagnostic Troubleshooting procedure before proceeding. Testing and Inspection

Diagnostic Test

1. CHECK FOR RELATED DTCS
With the scan tool, check for other transmission DTCs.
Is the DTC P0933 present also?

Yes

- Diagnose and repair the DTC(s).

No

- Go to 2

2. CHECK IF THE DTC 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 3

No

- Go to 11

3. CHECK THE LINE PRESSURE SENSOR CONNECTION
Ignition on, engine not running.
With the scan tool, monitor the Line Pressure, firmly push the Line Pressure Sensor harness connector towards the Transmission.
Did the Line Pressure change to about 207 kPa (30 psi) or 0.7 volts when the connector was pushed?

Yes

- Disconnect and properly reconnect the Line Pressure Sensor connector. Inspect terminals and repair as necessary.
- Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST. Transmission Verification Test

No

- Go to 4

4. CHECK THE PCM AND WIRING
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 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.

Install the Transmission Simulator, Miller tool #8333.
With the Transmission Simulator select the "OFF" position on the "Input/Output Speed" switch.
Ignition on, engine not running.
With the scan tool, monitor the Line Pressure during the following steps.
Using the Transmission Simulator, set the rotary knob to each of the 3 line pressure positions.

NOTE: All three scan tool Line Pressure readings should be steady and ±14 kPa (2.0 psi) or 0.1 volts of the reading specified on the Transmission Simulator.

Did the Line Pressure read within ±14 kPa (2.0psi) or 0.1 volts in all three positions?

Yes

- Go to 5

No

- Go to 7

5. CHECK THE LINE PRESSURE SENSOR
Turn the ignition off to the lock position.
Disconnect the Transmission Simulator, Miller tool #8333 and reconnect all previously disconnected connectors.
Install the Line Pressure Adaptor, Miller tool #8259, and the Pressure Gauge, Miller tool #C-3293, 0 to 2000 kPa or 0 to 300 psi.
Start the engine in park.
Monitor the line pressure readings of both the scan tool and the pressure gauge and compare the two readings.
Is the line pressure gauge reading within 34 kPa or 5 psi of the scan tool reading?

Yes

- Go to 6

No

- Replace the Line Pressure Sensor.
- Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST. Transmission Verification Test

6. CHECK FOR A PLUGGED TRANSMISSION OIL FILTER
Turn the ignition off to the lock position.
Remove and inspect the Transmission Oil Pan for excessive debris.
Remove and inspect the Primary Oil Filter.

NOTE: Make sure the Primary Transmission Oil Filter and/or O-ring is not cracked or split.

Does the Oil Pan contain excessive debris and/or is the Primary Oil Filter cracked or plugged?

Yes

- Repair the plugged, cracked, or split Primary Transmission Oil Filter and/or O-ring. If the Primary Transmission Oil Filter is plugged refer to the Service Information for the proper Hydraulic repair procedure.
- Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST. Transmission Verification Test

No

- Repair internal transmission and inspect the Transmission Oil Pump and replace if necessary. If no problem is found, replace the Solenoid/TRS Assembly.
- Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST. Transmission Verification Test

7. CHECK THE (F856) 5-VOLT SUPPLY CIRCUIT FOR A SHORT TO VOLTAGE




Disconnect the Transmission Simulator, Miller tool #8333.
Reconnect all previously disconnected connectors except the Line Pressure Sensor harness connector.
Ignition on, engine not running.
Measure the voltage of the (F856) 5-volt Supply circuit in the Line Pressure Sensor harness connector.
Is the voltage above 5.5 volts?

Yes

- Repair the (F856) 5-volt Supply circuit for a short to voltage.
- Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST. Transmission Verification Test

No

- Go to 8

8. CHECK THE (F856) 5-VOLT SUPPLY CIRCUIT FOR AN OPEN




Turn the ignition off to the lock position.
Disconnect the PCM C1 harness connector and connect Miller tool #8815.

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 (F856) 5-volt Supply circuit between the Line Pressure Sensor harness connector and the appropriate terminal of Miller tool #8815.
Is the resistance above 5.0 ohms?

Yes

- Repair the (F856) 5-volt Supply circuit for an open.
- Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST. Transmission Verification Test

No

- Go to 9

9. CHECK THE (F856) 5-VOLT SUPPLY CIRCUIT FOR A SHORT TO GROUND




Measure the resistance between ground and the (F856) 5-volt Supply circuit.
Is the resistance below 5.0 ohms?

Yes

- Repair the (F856) 5-volt Supply circuit for a short to ground.
- Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST. Transmission Verification Test

No

- Go to 10

10. CHECK THE (T118) LP VFS CONTROL CIRCUIT FOR A SHORT TO ANOTHER CIRCUIT




Turn the ignition off to the lock position.
Disconnect the Transmission Solenoid/TRS Assembly harness connector.
Disconnect all PCM harness connectors.
Measure the resistance between the (T118) LP VFS Control circuit and all other circuits in the Transmission Solenoid/TRS Assembly harness connector.
Is the resistance below 5.0 ohms between the (T118) Pressure Control Solenoid Control circuit and any other circuit(s) in the Transmission Solenoid/TRS Assembly harness connector?

Yes

- Repair the (T118) LP VFS Control circuit for a short to another circuit(s).
- Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST. Transmission Verification Test

No

- 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 45RFE/545RFE TRANSMISSION VERIFICATION TEST. Transmission Verification Test

11. CHECK WIRING AND CONNECTORS
The conditions necessary to set this 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.
Where there any problems found?

Yes

- Repair as necessary.
- Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST. Transmission Verification Test

No

- Test Complete.