NAG1 Automatic Transmission

P0748 - MODULATING PRESSURE SOLENOID CIRCUIT





When Monitored and Set Condition

- When Monitored: Always monitored with system active at each ignition cycle.
- Set Condition: If the TCM detects a short to ground, a short to voltage on the solenoid control circuit, a shorted solenoid, an open solenoid, or an open or shorted solenoid control circuit driver in the TCM.





For a complete Transmission Control Module Circuit Diagram, [1][2]Automatic Transmission/Transaxle.

Diagnostic Test

1. PRE-DIAGNOSTIC CHECK OUT
NOTE: Low fluid level can be the cause of many transmission problems. If the fluid level is low, locate and repair the leak then check and adjust the fluid level.

NOTE: Always perform diagnostics with a fully charged battery to avoid false symptoms.

With the scan tool, read Engine DTCs. Check and repair all engine DTCs prior to performing transmission symptom diagnostics.
With the scan tool, read and record all Transmission DTCs.

NOTE: Check connectors - Clean/repair as necessary. Poor pin to terminal connections can set DTCs.

Using the wiring diagram/schematic as a guide, inspect the wiring and connectors. Repair as necessary.
Most DTCs set on start up but some must be set by driving the vehicle such that all diagnostic monitors have run.

NOTE: Check for any Technical Service Bulletins that may apply.

Perform this procedure prior to Symptom diagnosis.

Continue

- Go to 2

2. CHECK FOR CURRENT DTC
NOTE: If the TCM detects and stores a DTC, the TCM also stores the engine/vehicle operating conditions under which the DTC was set. Some of these conditions are displayed on the scan tool at the same time the DTC is displayed.

NOTE: Before erasing stored DTCs, record these conditions. Attempting to duplicate these conditions may assist when checking for an active DTC.

Turn the ignition on.
With the scan tool, erase Transmission DTCs.

NOTE: It maybe necessary to road test the vehicle for this DTC to set.

With the scan tool, read Transmission DTCs.
Did this DTC set again?

Yes

- Go To 3

No

- Go To 7

3. MODULATING PRESSURE SOLENOID CONTROL CIRCUIT OPEN




Turn the ignition off.
Disconnect the Transmission Control Module C2 harness connector.
Disconnect the Transmission Solenoid Assembly harness connector.

NOTE: Check connectors - Clean/repair as necessary.

Measure the resistance of the Modulating Pressure Solenoid Control circuit from the TCM C2 harness connector to the Transmission Solenoid Assembly harness connector.
Is the resistance below 5.0 ohms?

Yes

Go To 4

No

- Repair the Modulating Pressure Solenoid Control circuit for an open.
- Perform NAG1 TRANSMISSION VERIFICATION TEST. Transmission Verification Test

4. MODULATING PRESSURE SOLENOID CONTROL CIRCUIT SHORT TO GROUND




With the ignition off.
Measure the resistance between ground and the Modulating Pressure Solenoid Control circuit.
Is the resistance above 100 kohms?

Yes

- Go To 5

No

- Repair the Modulating Pressure Solenoid Control circuit for a short to ground.
- Perform NAG1 TRANSMISSION VERIFICATION TEST. Transmission Verification Test

5. MODULATING PRESSURE SOLENOID CONTROL CIRCUIT SHORT TO OTHER CIRCUITS




With the ignition off.
Measure the resistance between the Modulating Pressure Solenoid Control circuit and all other circuits in the Transmission Solenoid Assembly harness connector.
Is the resistance above 100 kohms for all measurements?

Yes

- Go To 6

No

- Repair the Modulating Pressure Solenoid Control circuit for a short to other circuits.
- Perform NAG1 TRANSMISSION VERIFICATION TEST. Transmission Verification Test

6. MODULATING PRESSURE SOLENOID RESISTANCE OUT OF TOLERANCE




With the ignition off.
Reconnect the Transmission Solenoid Assembly harness connector.
Measure the resistance between the Modulating Pressure Solenoid Control circuit and the Solenoid Supply Voltage circuit at the Transmission Control Module C2 harness connector.
Is the resistance between 2.5 and 6.5 ohms?

Yes

- Replace the Transmission Control Module. Transmission Control Module - Removal.
- Perform NAG1 TRANSMISSION VERIFICATION TEST. Transmission Verification Test

No

- Replace the Modulating Pressure Solenoid. Removal.
- Perform NAG1 TRANSMISSION VERIFICATION TEST. Transmission Verification Test

7. INTERMITTENT WIRING AND CONNECTORS
The condition that caused this DTC to set is currently not present. Inspect the related wiring harness for a possible intermittent condition.
Using the schematics as a guide, inspect the wiring and connectors specific to this circuit.
Wiggle the wires while checking for shorts and open circuits.

NOTE: Check for any Technical Service Bulletins that may apply.

Were any problems found?

Yes

- Repair as necessary
- Perform NAG1 TRANSMISSION VERIFICATION TEST. Transmission Verification Test

No

Test Complete.