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 10 psi below Desired Line Pressure, this DTC will set.
Always perform the 42RLE Pre-Diagnostic Troubleshooting procedure before proceeding. Initial Inspection and Diagnostic Overview
Diagnostic Test
1. CHECK FOR RELATED DTCS
With the scan tool, read DTCs
Is the DTC P0932 present also?
Yes
- Diagnose and repair 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 10
3. CHECK THE PCM AND WIRING USING THE TRANSMISSION SIMULATOR
Turn the ignition off to the lock position.
Remove the from the TIPM.
CAUTION: Removal of the from the TIPM will prevent the vehicle from being started in gear.
WARNING: The 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.
On the Transmission Simulator select the "OFF" position of 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 or 2.0 psi of the reading specified on the Transmission Simulator.
Did the Line Pressure read within ± 14 kPa or 2.0 psi in all three positions?
Yes
- Go to 4
No
- Go to 6
4. 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 a Pressure Gauge, 0 to 2000 kPa or 0 to 300 psi to the L/R test port.
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 5
No
- Replace the Line Pressure Sensor.
- Perform 42RLE TRANSMISSION VERIFICATION TEST Transmission Verification Test
5. 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 Transmission Oil Filter.
Does the Oil Pan contain excessive debris and/or is the Transmission Oil Filter plugged?
Yes
- Repair as necessary. If the Transmission Oil Filter is plugged or there is excessive debris, refer to the Service Information for the proper Hydraulic repair procedure.
- Perform 42RLE TRANSMISSION VERIFICATION TEST Transmission Verification Test
No
- Repair internal transmission and inspect the Transmission Oil Pump and replace if necessary.
- Perform 42RLE TRANSMISSION VERIFICATION TEST Transmission Verification Test
6. CHECK THE (F856) 5-VOLT SUPPLY CIRCUIT FOR A SHORT TO VOLTAGE
Disconnect the Transmission Simulator, Miller tool #8333 and the Electronic Transmission Adapter kit.
Reconnect all previously disconnected connectors except the Line Pressure Sensor/Variable Force Solenoid Assembly harness connector.
Ignition on, engine not running.
Measure the voltage of the (F856) 5-volt Supply circuit.
Is the voltage above 5.5 volts?
Yes
- Repair the (F856) 5-volt Supply circuit for a short to voltage.
- Perform 42RLE TRANSMISSION VERIFICATION TEST Transmission Verification Test
No
- Go to 7
7. 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/Variable Force Solenoid Assembly 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 42RLE TRANSMISSION VERIFICATION TEST Transmission Verification Test
No
- Go to 8
8. 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 42RLE TRANSMISSION VERIFICATION TEST Transmission Verification Test
No
- Go to 9
9. CHECK THE (T118) LP VFS CONTROL CIRCUIT FOR A SHORT TO ANOTHER CIRCUIT
Turn the ignition off to the lock position.
Disconnect the Line Pressure Sensor/Variable Force Solenoid Assembly harness connector.
Disconnect all PCM harness connectors.
Measure the resistance between the (T118) LP VFS Control circuit and all other circuits in the Line Pressure Sensor/Variable Force Solenoid Assembly harness connector.
Is the resistance below 5.0 ohms between the (T118) LP VFS Control circuit and any other circuit(s) in the Line Pressure Sensor/Variable Force Solenoid Assembly harness connector?
Yes
- Repair the (T118) LP VFS Control circuit for a short to another circuit(s).
- Perform 42RLE 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 42RLE TRANSMISSION VERIFICATION TEST Transmission Verification Test
10. CHECK THE 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 42RLE TRANSMISSION VERIFICATION TEST Transmission Verification Test
No
- Test Complete.