P0868 Jeep OBD Code Diagnostic Procedure

P0868 Jeep OBD Code

LINE PRESSURE LOW

For a complete wiring diagram Refer to Section 8W.

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.

 

Possible Causes
CHECK FOR RELATED DTC’S
LOW FLUID LEVEL
(F856) 5-VOLT SUPPLY CIRCUIT OPEN
(F856) 5-VOLT SUPPLY CIRCUIT SHORT TO GROUND
(F856) 5-VOLT SUPPLY CIRCUIT SHORT TO VOLTAGE
(T118) PRESSURE CONTROL SOLENOID CONTROL CIRCUIT SHORT TO ANOTHER CIRCUIT
INTERNAL TRANSMISSION
LINE PRESSURE SENSOR
CRACKED, PLUGGED, OR MIS-INSTALLED PRIMARY OIL FILTER
STUCK OR STICKING MAIN REGULATOR VALVE
POWERTRAIN CONTROL MODULE

Always perform the 42RLE Pre-Diagnostic Troubleshooting procedure before proceeding.

(Refer to 21 – TRANSMISSION/TRANSAXLE/AUTOMATIC- 42RLE – STANDARD PROCEDURE)

Diagnostic Test

1. CHECK FOR RELATED DTCS

With the scan tool, check for other transmission DTCs

Is the DTC P0932 present also?
Yes

  • Refer to the Transmission category and perform the appropriate symptom.

No

  • Go To 2


2. CHECK IF THE DTC IS CURRENT

With the scan tool, check the STARTS SINCE SET counter for P0868.

NOTE:
This counter only applies to the last DTC set.

Is the STARTS SINCE SET COUNTER 2 or less?

Yes

  • Go To 3

No

  • Go To 10

3. CHECK THE PCM AND WIRING

Turn the ignition off to the lock position.

Remove the Ignition Switch Feed fuse from the TIPM.

CAUTION:
Removal of the Ignition Switch Feed fuse from the TIPM will prevent the vehicle from being started in gear.

WARNING:
The Ignition Switch Feed fuse 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 per the Service Information.

 

  • Perform 42RLE TRANSMISSION VERIFICATION TEST(Refer to 21 – TRANSMISSION/TRANSAXLE/AUTOMATIC – 42RLE – STANDARD PROCEDURE)

 

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 per the Service Information.
  • 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, refer to the Service Information for the proper Hydraulic repair
    procedure.

 

  • Perform 42RLE TRANSMISSION VERIFICATION TEST(Refer to 21 – TRANSMISSION/TRANSAXLE/AUTOMATIC – 42RLE – STANDARD PROCEDURE)

 

No

  • Repair internal transmission and inspect the Transmission Oil Pump per the Service Information and replace if necessary.

 

  • Perform 42RLE TRANSMISSION VERIFICATION TEST(Refer to 21 – TRANSMISSION/TRANSAXLE/AUTOMATIC – 42RLE – STANDARD PROCEDURE)

 

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(Refer to 21 – TRANSMISSION/TRANSAXLE/AUTOMATIC – 42RLE – STANDARD PROCEDURE)

 

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(Refer to 21 – TRANSMISSION/TRANSAXLE/AUTOMATIC – 42RLE – STANDARD PROCEDURE)

 

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(Refer to 21 – TRANSMISSION/TRANSAXLE/AUTOMATIC – 42RLE – STANDARD PROCEDURE)

 

No

  • Go To 9

9. CHECK THE (T118) PRESSURE CONTROL SOLENOID 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) Pressure Control Solenoid 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) Pressure Control Solenoid Control circuit and any other circuit(s) in the Line Pressure Sensor/Variable Force Solenoid Assembly harness connector?

Yes

  • Repair the (T118) Pressure Control Solenoid Control circuit for a short to another circuit(s).

 

  • Perform 42RLE TRANSMISSION VERIFICATION TEST(Refer to 21 – TRANSMISSION/TRANSAXLE/AUTOMATIC – 42RLE – STANDARD PROCEDURE)

 

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 per the Service Information. With the scan tool, perform QUICK LEARN.

 

  • Perform 42RLE TRANSMISSION VERIFICATION TEST(Refer to 21 – TRANSMISSION/TRANSAXLE/AUTOMATIC – 42RLE – STANDARD PROCEDURE)

 

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 42RLE TRANSMISSION VERIFICATION TEST(Refer to 21 – TRANSMISSION/TRANSAXLE/AUTOMATIC – 42RLE – STANDARD PROCEDURE)

 

No

  • Test Complete.
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