P0944-LOSS OF HYDRAULIC PUMP PRIME

For a complete wiring diagram Refer to Section 8W

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 cracked oil filter.

The Loss of Prime DTC 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:
If the transmission is slipping in any forward gear and all the pressure switches are not indicating pressure, a loss of prime test is run.
Set Condition:
If the transmission begins to slip in a forward gear and all the pressure switch(s) that should be closed are open a loss of prime test begins. Available elements are turned on by the PCM to see if pump prime exists. The DTC sets if no pressure switch(s) respond.

Possible Causes

SHIFT LEVER OUT OF ADJUSTMENT

IMPROPER FLUID LEVEL

CRACKED OR IMPROPERLY INSTALLED PRIMARY OIL FILTER OR SEAL

LOOSE COOLER RETURN FILTER

STUCK OR STICKING MAIN REGULATOR VALVE

TRANSMISSION OIL PUMP

Always perform the 45RFE/545RFE Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - 45RFE/545RFE - STANDARD PROCEDURE)

Diagnostic Test

1.SHIFT LEVER POSITION TEST

Did the Shift Lever Position Test pass?

Yes

Go To 2

Refer to the Transmission category and perform the appropriate symptom.
Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - 45RFE/545RFE - STANDARD PROCEDURE)

2.CHECK TO SEE IF DTC P0944 IS CURRENT

Does the Line Pressure match the Desired Line Pressure within ± 5 psi?

No

Go To 6

Yes

Go To 3

3.CHECK LINE PRESSURE IN DRIVE AND REVERSE

Does the Line Pressure match the Desired Line Pressure within ± 5 psi in all gear ranges?

Yes

Go To 4

Go To 5

4.REVIEW CUSTOMER COMMENTS

Has the customer experienced any delayed engagement and/or "No Drive" conditions?

Yes

Repair internal transmission as necessary. Replace the Transmission Oil Pump if inspection reveals no signs of internal seal leakage. Refer to the Service Information for the proper repair procedure.
Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - 45RFE/545RFE - STANDARD PROCEDURE)

Test Complete.

5.DTC VERIFICATION

Did any following DTCs set, P0868, P0944, P0841, P0846, P0871, P0876, or P0988?

Yes

Go To 6

Test Complete.

6.CHECK TRANSMISSION OIL FILTER

Does the Oil Pan contain excessive debris and/or is the Oil Filter plugged or seal damaged?

Yes

Repair the cause of the plugged transmission oil filter or excessive debris. Check the Transmission Oil Filter seal for improper installation onto filter neck instead of into the pump bore, not fully seated against pump housing, filter neck not engaged into pump. Repair as necessary.
Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - 45RFE/545RFE - STANDARD PROCEDURE)

Repair the Transmission Oil Pump as necessary. Check for a stuck main regulator valve and clean if necessary. Refer to the Service Information for the proper repair procedure.
Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - 45RFE/545RFE - STANDARD PROCEDURE)