Circuit Description
The Pressure Control (PC) solenoid assembly is a precision electronic pressure regulator that controls transmission line pressure based on current flow through its coil windings. The magnetic field produced by the coil moves the solenoid's internal valve which varies pressure to the pressure regulator valve. The Transmission Control Module (TCM) controls the PC solenoid assembly by applying a varying amount of current to the solenoid. The applied current can vary from 0.1 to 1.1 amps. Low current (0.1 amp) indicates a high line pressure. High current (1.1 amps) indicates low line pressure. An internal current monitor within the TCM provides feedback to determine actual PC solenoid assembly current draw.
The TCM controls the PC solenoid assembly on a positive duty cycle at a fixed frequency. The high (positive) side of the PC solenoid electrical circuit at the TCM (terminal X1-3) controls the PC solenoid assembly operation. The TCM (terminal X1-29) provides a ground path for the circuit, monitors average current and continuously varies the PC solenoid valve duty cycle to maintain the correct average current flowing through the PC solenoid assembly.
The duty cycle of the PC solenoid assembly is expressed as a percentage of energized ON time. Zero percent indicates zero ON time (non-energized) or no current flow. Approximately 60% at idle indicates maximum ON time (energized) or high current flow. The TCM determines the appropriate line pressure for a given load by comparing various inputs including throttle position, transmission fluid temperature and gear state.
If the TCM detects a continuous open, short to voltage or short to ground in the PC solenoid circuit, then DTC P0748 sets, which is a type 'C' DTC.
Conditions for Running the DTC
| • | Ignition voltage is between 8.0 and 18.0 volts. |
| • | The engine is running. |
Conditions for Setting the DTC
The PC solenoid assembly feedback circuit indicates a continuous open or short to ground for greater than 1.2 seconds.
Action Taken When the DTC Sets
| • | The TCM does not request the Powertrain Interface Module (PIM) to illuminate the Check Powertrain Malfunction Indicator Lamp (MIL). |
| • | The TCM records the operating conditions when the 'Conditions for Setting the DTC' have been met. The TCM stores this information as a Failure Record. |
| • | The TCM also turns off the pressure control solenoid (causing maximum line pressure). |
| • | The TCM freezes the transmission adaptive learning function. |
| • | The TCM stores DTC P0748 into TCM history. |
Conditions for Clearing the DTC
| • | Tech 2 can clear the DTC. |
| • | The TCM clears the DTC from its memory (history DTC) if the vehicle completes 40 warm-up cycles without a non-emission related DTC occurring. |
| • | The TCM cancels the default actions when the ignition is off long enough to power down the TCM. |
Step | Action | Values | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
Schematic Reference: Automatic Transmission Controls Schematics For information on testing wiring faults, refer to Wiring Systems. | ||||||||
1 | Has the Diagnostic System Check - Automatic Transmission been completed? | -- | Go to Step 2 | |||||
2 |
Does the PC Sol. Actual Current reading vary from the PC Sol. Ref. Current by more than the specified amount? | 0.05 Amps | Go to Step 3 | Go to Testing for Intermittent Conditions and Poor Connections | ||||
3 |
Is the voltage reading less than specified? | 0.3 Volts | Go to Step 4 | Go to Step 8 | ||||
4 |
Is the resistance reading greater than specified? | 500 kΩ | Go to Step 5 | Go to Step 10 | ||||
5 | Using a digital ohmmeter, measure the resistance between transmission wiring harness TCM connector A112-T68, terminals X1-3 (PCS high control) and X1-29 (PCS low control). Is the resistance reading within the specifications? | 3.5-4.6 Ω @ 20° 4.2-5.5 Ω @ 70° | Go to Step 6 | If reading is more than specified, go to Step 13. If reading is less than specified, go to Step 14. | ||||
6 |
Does the solenoid click as the jumper wire is connected? | -- | Go to Step 7 | If PC PWM solenoid assembly is faulty, replace the solenoid. Refer to Transmission Control Module Replacement Go to Step 15 | ||||
7 | Replace the TCM. Refer to Refer to Transmission Control Module Replacement for replacement procedures. Is the replacement complete? | -- | Go to Step 15 | -- | ||||
8 |
Does either check indicate a short to voltage in the wiring? | -- | Repair short to voltage in relevant circuits. Go to Step 15 | Go to Step 9 | ||||
9 |
Is the transmission internal wiring harness OK? | -- | If the PC PWM solenoid assembly is faulty, replace the solenoid. Refer to Pressure Control Solenoid Valve Replacement Go to Step 15 | Replace the transmission internal wiring harness. Refer to Transmission Internal Electrical Harness Replacement Go to Step 15 | ||||
10 |
Is the resistance reading greater than specified? | 500 kΩ | Go to Step 11 | Go to Step 12 | ||||
11 | Using a digital voltmeter, check the wiring for a short to ground condition between transmission wiring harness TCM connector A112-T68, terminals X1-29 and transmission wiring harness connector X121-X1, terminal X1-8. Does the check indicate a short to ground in the wiring? | -- | Repair the short to ground in relevant circuit. | Replace the faulty PCS PWM solenoid assembly. Refer to Pressure Control Solenoid Valve Replacement Go to Step 15 | ||||
12 | Using a digital voltmeter, check the wiring for a short to ground condition between transmission wiring harness TCM connector A112-T68, terminals X1-3 and transmission wiring harness connector X121-X1, terminal X1-13. Does the check indicate a short to ground in the wiring? | -- | Repair the short to ground in relevant circuit. Go to Step 15 | -- | ||||
13 |
Does either check indicate an open circuit or high resistance in the wiring? | -- | Repair cause of the open circuit or high resistance in relevant circuit. Go to Step 15 | Go to Step 9 | ||||
14 | Using a digital voltmeter, check for an internal short circuit condition between transmission wiring harness TCM connector A112-T68 and transmission wiring harness connector X121-X1, circuits 1228 and 1229. Does the check indicate an internal short circuit condition in the wiring? | -- | Repair cause of the internal short circuit condition in relevant circuits. Go to Step 15 | Go to Step 9 | ||||
15 | Perform the following procedure to verify the repair:
Operate the vehicle under the following conditions:
Has the test run and passed? | -- | Go to Step 16 | Go to Step 2 | ||||
16 | With the Tech 2, observe the stored information, capture information and DTC information. Does the Tech 2 display any DTCs that have not been diagnosed? | -- | System OK | |||||
When all diagnosis and repairs are completed, clear all DTCs and verify correct operation. | ||||||||
