Circuit Description
During normal driving modes, the PCM/TC adapts line pressure to prevent clutch
slip and harsh shifts. This is accomplished by modulating the pressure control solenoid
ground, 1530, to raise or lower pressure. An open circuit equals high pressure. A
grounded circuit equals low pressure. If the time required to make all shifts is too
short and line pressure has been commanded low, it is determined that the actual line
pressure is too high.
Conditions for Setting the DTC
DTC P0748 is set when the PCM has detected the following conditions for more
than 5 shifts:
| • | Upshift pressure adaptive error is less than 112 which indicates
over pressure. This condition must still exist after the up shift pressure adaptives
have reached the lower limit. Low limit equals 0.288 kPa. |
| • | Low load, low command pressure |
| • | Transaxle fluid temperature is above 40°C (104°F). |
Test Description
Numbered steps below refer to numbered steps on the chart.
- Check for DTCs P0702, P0746, P0747, or P0749. They must be eliminated
first as a possible cause of a DTC P0748.
- Check the solenoid operation. Use the solenoid quick check in the test
section located at the end of the DTC charts. The solenoid quick test will PWM the
solenoids at a set rate. Listen and compare noise of the TFP solenoid to that of other
solenoids. The noise of all should be similar.
Important: To check solenoid operation, command the
solenoid quick test using the scan tool.
- Check the pressure regulator valve operation. Use the pressure test in the test
section at the end of the DTC charts. Make sure the pressure increases in correct
increments during the pressure test. If the pressure changes erratically or move in
large increments, the pressure regulator valve is probably sticking.
- If little or no pressure change, the regulator valve is stuck. To verify,
test for minimum and maximum oil pressure per oil pressure specification in the test
section at the end of the DTC charts.
Repair Verification
Monitor the DTC menu Code Status for Pass Since Code Clear and Pass This Ignition
Cycle. When both have passed, the repair is verified.
Criteria for pass:
| • | Power is present at the solenoids and no active faults exist for this
solenoid. |
Diagnostic Aids
| • | When the PCM detects a fault in the circuit, an open, ground, or short,
the PCM will open the circuit internally to protect the circuit. |
| • | There could be a hot or cold only condition. If the condition is intermittent,
try to reproduce the DTC by checking the malfunction history table with the scan tool
to see at what temperature the DTC will set and reproduce the conditions. |
| • | This DTC may set or intermittent harsh upshifts may be caused by a poor
electrical connection at either the PCM, solenoid connector plate, or UHJB terminals.
Wiggling the connectors while performing an actuator quick test may isolate the problem
area. |
