P0944

P0944-LOSS OF HYDRAULIC PUMP PRIME



Theory of Operation

The Loss of Prime Test is used to prevent transmission defaults and erroneous fault codes during temporary loss of pump prime that may occur with low transmission fluid under severe braking conditions, start-up, etc. and to point towards more subtle problems such as a plugged or ruptured oil filter. The Loss of Prime fault is set by a loss of hydraulic pressure in the transmission system. This condition, if sustained, will result in the vehicle being unable to move.

- When Monitored:
Every 350 msec

- Set Condition:
If the transmission begins to slip in any forward gear, and the pressure switch or switches that should be closed for a given gear are open, a loss of prime test begins. All available elements (in 1st gear LR, 2/4 and OD, in 2nd, 3rd, and 4th gear 2/4 and OD) are turned on by the Powertrain Control Module (PCM) to see if pump prime exists. The code is set if none of the pressure switches respond. The PCM will continue to run the loss of prime test until pump pressure returns. The vehicle will not move or the transmission will slip. Normal operation will continue if pump prime returns.





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

1. CHECK TO SEE IF DTC P0944 IS CURRENT
1. Place the gear selector in park.
2. Start the engine.
3. Check the fluid level and fill as required.

NOTE: The Transmission Temperature must be at least 43° C (110° F) before performing the following steps.

4. The Transmission must be at operating temperature prior to checking pressure. Cold transmission fluid will result in higher pressure readings.
5. Place the Transmission in Drive.
6. With the scan tool, observe the Transmission Pressure Switch states.

Are any of the Pressure Switches closed?

Yes

- Go To 2

No

- Go To 3

2. INTERMITTENT OPERATION
1. The conditions necessary to set this DTC are not present at this time.
2. Test drive the vehicle. Allow the Transmission to shift through all gears and ranges.

Was a delayed engagement and/or a no drive condition present during the test drive?

Yes

- Go To 3

No

- Go To 5

3. SHIFT LEVER POSITION TEST
1. With the scan tool, perform a Shift Lever Position test. Follow the instructions on the screen.

Did the Shift Lever Position Test pass?

Yes

- Go To 4

No

- P0706 Perform the diagnostic procedure for P0706-TRANSMISSION RANGE SENSOR RATIONALITY.
- Perform the appropriate TRANSMISSION VERIFICATION TEST.

4. CHECK FOR PLUGGED TRANSMISSION FILTER
1. Remove the Transmission Pan and inspect the Transmission Fluid and Transmission Filter.

Does the Transmission Oil Pan contain excessive debris and/or is the Oil Filter cracked, broken, or plugged?

Yes

- Replace the Transmission Filter. If excessive debris is present, remove transmission, inspect all clutches, and repair as required. Refer to the Service Information for the proper repair procedure.
- Perform the appropriate TRANSMISSION VERIFICATION TEST. .

No

- Remove the valve body and inspect the main regulator valve for sticking in its bore. Clean or replace as required. If no problems are found, replace the Transmission Oil Pump.
- Perform the appropriate TRANSMISSION VERIFICATION TEST. .

5. CHECK THE WIRING AND CONNECTORS
1. The conditions necessary to set this DTC are not present at this time.
2. Using the schematics as a guide, inspect the wiring and connectors specific to this circuit.
3. Wiggle the wiring while checking for shorted and open circuits.
4. With the scan tool, check the Event Data to help identify the conditions in which the DTC was set.

Were there any problems found?

Yes

- Repair as necessary.
- Perform the appropriate TRANSMISSION VERIFICATION TEST. Verification Tests.

No

- Test Complete.