68RFE Automatic Transmission

P0934-LINE PRESSURE SENSOR CIRCUIT LOW





For a complete wiring diagram refer to Diagrams/Electrical. Electrical Diagrams


Theory of Operation


Line pressure is electronically controlled by the Transmission Control System and is measured by the Line Pressure Sensor (LPS). The desired line pressure is continuously being compared to the actual line pressure and is regulated by electronically changing the duty cycle of the Pressure Control Solenoid (PCS). (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 the transmission and engine. A calculated torque input to the transmission is used as the primary input of the desired line pressure calculation and is called Torque Based Line Pressure. In addition, the line pressure is set to a preset level 1034 to 1103 kPa (150 to 160 psi) during shifts to ensure consistent shift quality.


The monitored Line Pressure Sensor voltage should always be between 0.35 and 4.75 volts. Any monitored voltages outside these parameters indicate an Line Pressure Sensor or wiring problem and will cause either DTC P0934 or P0935 to set.


- When Monitored:

Continuously with the ignition on and engine running.

- Set Condition:

This DTC will set when the monitored Line Pressure Sensor voltage is less than or equal to 0.35 volts for 0.18 seconds.







Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. 68RFE Pre-Diagnostic Troubleshooting Procedure

Diagnostic Test


1. CHECK IF DTC IS CURRENT

With the scan tool, check the STARTS SINCE SET counter for P0934.


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

Is the STARTS SINCE SET counter 2 or less?

Yes

- Go To 2

No

- Go To 7



2. 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.

Ignition on, engine not running.

With the scan tool, under Transmission Sensors, monitor the Line Pressure.

Using the Transmission Simulator, set the rotary switch to each of the 3 line pressure positions.


NOTE: The readings should be within ±14 kPa (2.0 psi) or 0.1 volts on the scan tool to the pressure readings specified on Transmission Simulator.

Does the Line Pressure on the scan tool match the line pressures on the Transmission Simulator?

Yes

- Replace the Line Pressure Sensor.
- Perform 68RFE TRANSMISSION VERIFICATION TEST. 68RFE Transmission Verification Test

No

- Go To 3



3. CHECK THE (T38) LINE PRESSURE SENSOR SIGNAL CIRCUIT FOR A SHORT TO GROUND





Turn the ignition off to the lock position.

Disconnect the PCM C4 harness connector and connect Miller tool #8815.

Disconnect the Transmission Simulator, Miller tool #8333.


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 between ground and the (T38) Line Pressure Sensor Signal circuit.

Is the resistance below 5.0 ohms?

Yes

- Repair the (T38) Line Pressure Sensor Signal circuit for a short to ground.
- Perform 68RFE TRANSMISSION VERIFICATION TEST. 68RFE Transmission Verification Test

No

- Go To 4



4. CHECK THE (T38) LINE PRESSURE SENSOR SIGNAL CIRCUIT FOR AN OPEN





Disconnect the PCM C4 harness connector and connect Miller tool #8815.

Measure the resistance of the (T38) Line Pressure Sensor Signal 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 (T38) Line Pressure Sensor Signal circuit for an open.
- Perform 68RFE TRANSMISSION VERIFICATION TEST. 68RFE Transmission Verification Test

No

- Go To 5



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





Disconnect the PCM C1 harness connector and connect Miller tool #8815.

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 below 5.0 ohms?

Yes

- Repair the (F856) 5-volt Supply circuit for an open.
- Perform 68RFE TRANSMISSION VERIFICATION TEST. 68RFE Transmission Verification Test

No

- Go To 6



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





Disconnect the PCM C1 harness connector and connect Miller tool #8815.

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 68RFE TRANSMISSION VERIFICATION TEST. 68RFE 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 the PCM. With the scan tool, perform QUICK LEARN.
- Perform 68RFE TRANSMISSION VERIFICATION TEST. 68RFE Transmission Verification Test


7. 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 68RFE TRANSMISSION VERIFICATION TEST. 68RFE Transmission Verification Test

No

- Test Complete.