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 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 ms

  • 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 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.


Possible Causes
  
LOW TRANSMISSION FLUID LEVEL
  
SHIFT LEVER POSITION
  
PLUGGED TRANSMISSION FILTER
  
TRANSMISSION OIL PUMP
  

Always perform the 42RLE Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - 42RLE - STANDARD PROCEDURE)



Diagnostic Test

1.CHECK TO SEE IF DTC P0944 IS CURRENT



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






Are any of the Pressure Switches closed?

Yes
  • Go To 2


No
  • Go To 4

2.INTERMITTENT OPERATION




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

Yes
  • Go To 4


No
  • Go To 3

3.INTERMITTENT WIRING AND CONNECTORS






Were there any problems found?

Yes


No
  • Test Complete.

4.SHIFT LEVER POSITION TEST



Did the Shift Lever Position Test pass?

Yes
  • Go To 5


No

5.CHECK FOR PLUGGED TRANSMISSION FILTER



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

Yes


No