P0748

Diagnostic Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION

The Pressure Control Solenoid is inside of the transmission adapter case. The pressure solenoid makes allows for the Transmission Control Module (TCM) to optimize the line pressure in the transmission for various driving conditions.

Pressure regulation depends on heavily on throttle position. The TCM receives throttle position from the ECM. This data is part of the Pulse Width Modulated (PWM) encoded ECM Data Signal to the TCM. This signal processes in the TCM which adjusts the transmission line pressure.

Occasionally during normal operation, the Pressure Control Solenoid is cycled to prevent the spool valve from becoming stuck. The cycling finishes without a significant affect on the line pressure.

The Pressure Control Solenoid is supplied power via the Transmission Power Relay (internal to the TCM). The TCM controls the solenoid by grounding the control circuit via an internal solid state device called a driver. The primary function of the driver is to supply the ground for the component being controlled. For this particular component, the TCM monitors the Current draw in order to monitor the circuit operation. When the TCM is commanding the Pressure Control Solenoid on, the control circuit current should be high (about 1.2 A). When the TCM is commanding the Pressure Control Solenoid off, the current on the circuit should be low (less than 100 mA). If the fault detection circuitry senses a current other than what is expected, this DTC will set.

CONDITIONS FOR RUNNING THE DTC

Tests continuously

CONDITIONS FOR SETTING THE DTC

A short to ground, open circuit, or short to battery voltage detected on the control circuit.

ACTION TAKEN WHEN THE DTC SETS

^ The Malfunction Indicator Lamp (MIL)/Service Transmission Lamp (STL) will not illuminate.

^ The TCM memory stores the DTC at the time of the first failure.

CONDITIONS FOR CLEARING THE MIL/DTC

^ A History DTC clears after forty consecutive warm-up cycles if no failures are present by this or any other non-emission related diagnostic.

^ The scan tool clears the MIL/DTC.

DIAGNOSTIC AIDS

Use the Connector Test Adapter Kit J 35616-A for any test that requires probing the TCM harness connector or a component harness connector. Using this kit will prevent damage to the harness connector terminals.

Check for the following conditions:

^ Poor connections at the TCM or at the component. Inspect the harness connectors for any backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection. Refer to Overall Vehicle Information / Diagrams / Diagnostic Aids for Checking Terminal Contact procedure.

^ Damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the scan tool while moving any related connectors and any wiring harnesses. A change in the display may help to locate the fault.

TEST DESCRIPTION

The number(s) below refer to the step numbers on the diagnostic table.

2. Allows the TCM to determine if the fault is present now.

3. Listen for an audible click when the solenoid operates. Ground the circuit repeatedly if necessary.

4. This check can detect a partially shorted coil which would cause excessive current flow. Leaving the circuit energized for 2 minutes allows the coil to warm up. When the coil becomes warm, the coil may open (Amps drop to 0), or short (goes above 1.5 Amp).

5. Be sure to probe the correct Transmission Power Relay output circuit (there are two in the adapter case harness). Pins 54 and 40 are connected within the TCM.

16. If the solenoid checks out OK, and no trouble is found with the connections at the TCM, check the wiring and connections closely. If no trouble is found, the TCM may be the cause of the problem; however this would be an extremely unlikely failure.