P0868
P0868 - Line Pressure Low
For a complete wiring diagram, refer to.
Theory of Operation
Line pressure is measured by the line pressure sensor and regulation is achieved by changing the duty cycle of the pressure control solenoid 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 less than desired line pressure, this DTC will set.
Always perform the pre-diagnostic troubleshooting procedure before proceeding. Refer to => Non-DTC Based Diagnostics. Pre-Diagnostic Troubleshooting Procedure
Test Step 1 - Check for Related DTCs
• With the scan tool, read DTCs.
Is the DTC P0932 present also?
Yes
• Refer to the transmission category and perform the appropriate symptom.
No
• Go to Test Step 2.
Test Step 2 - Determine if the DTC is Current
• With the scan tool, check the STARTS SINCE SET counter for P0868.
• This counter only applies to the last DTC set.
Is the STARTS SINCE SET counter 2 or less?
Yes
• Go to Test Step 3.
No
• Go to Test Step 10.
Test Step 3 - Check the PCM and Wiring
The starter solenoid relay must be removed from the TIPM. Failure to do so can result in personal injury or death.
Removal of the starter solenoid relay from the TIPM will prevent the vehicle from being started in gear.
• Turn the ignition OFF to the lock position.
• Remove the starter solenoid relay from the TIPM.
• 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.
• All three scan tool Line Pressure readings should be steady and ± 14 kPa or 2.0 psi (0.2 volts) of the reading specified on the transmission simulator.
Did the line pressure read within ± 14 kPa or 2.0 psi (0.2 volts) in all three positions?
Yes
• Go to Test Step 4.
No
• Go to Test Step 6.
Test Step 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 line pressure 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 Test Step 5.
No
• Replace the transmission solenoid/TRS assembly.
• Perform the Transmission Verification Test. Refer to => Non-DTC Based Diagnostics. Transmission Verification Test
Test Step 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 per the service information.
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.
• Perform the Transmission Verification Test. Refer to => Non-DTC Based Diagnostics. Transmission Verification Test
No
• Repair internal transmission and inspect the transmission oil pump and replace if necessary.
• Perform the Transmission Verification Test. Refer to => Non-DTC Based Diagnostics. Transmission Verification Test
Test Step 6 - Check the 5 Volt supply Circuit for a Short to Voltage
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.
• Turn the ignition OFF to the lock position.
• Disconnect the PCM C1 harness connector and connect Miller tool #8815.
• Disconnect the transmission simulator, Miller tool #8333 and the electronic transmission adapter kit.
• Ignition ON, engine not running.
• Measure the voltage of the 5 volt supply circuit.
Is the voltage more than 5.5 volts?
Yes
• Repair the 5 volt supply circuit for a short to voltage.
• Perform the Transmission Verification Test. Refer to => Non-DTC Based Diagnostics. Transmission Verification Test
No
• Go to Test Step 7.
Test Step 7 - Check the 5 Volt Supply Circuit for an Open
• Turn the ignition OFF to the lock position.
• Measure the resistance of the 5 volt supply circuit between the transmission solenoid/TRS assembly harness connector and the appropriate terminal of Miller tool #8815.
Is the resistance more than 5.0 ohms?
Yes
• Repair the 5 volt supply circuit for an open.
• Perform the Transmission Verification Test. Refer to => Non-DTC Based Diagnostics. Transmission Verification Test
No
• Go to Test Step 8.
Test Step 8 - Check the 5 Volt Supply Circuit for a Short to Ground
• Measure the resistance between ground and the 5 volt supply circuit.
Is the resistance less than 5.0 ohms?
Yes
• Repair the 5 volt supply circuit for a short to ground.
• Perform the Transmission Verification Test. Refer to => Non-DTC Based Diagnostics. Transmission Verification Test
No
• Go to Test Step 9.
Test Step 9 - Check the LP VFS Control Circuit for a Short to Another Circuit
• Turn the ignition OFF to the lock position.
• Disconnect all PCM harness connectors.
• Measure the resistance between the pressure control line pressure circuit and all other circuits in the transmission solenoid/TRS assembly harness connector.
Is the resistance less than 5.0 ohms between the pressure control line pressure circuit and any other circuits in the line pressure sensor/variable force solenoid assembly harness connector?
Yes
• Repair the pressure control line pressure circuit for a short to another circuits.
• Perform the Transmission Verification Test. Refer to => Non-DTC Based Diagnostics. Transmission Verification Test
No
• Using the schematics as a guide, check the powertrain control module 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. Refer to With the scan tool, perform Quick Learn.
• Perform the Transmission Verification Test. Refer to => Non-DTC Based Diagnostics. Transmission Verification Test
Test Step 10 - Intermittent 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 DTC event data to help identify the conditions in which the DTC was set.
Where there any problems found?
Yes
• Repair as necessary.
• Perform the Transmission Verification Test. Refer to => Non-DTC Based Diagnostics. Transmission Verification Test
No
• Test Complete.