ECO Start/Stop Inoperative, Fault Code P0944 In Transmission Control Unit (LI27.57-P-053496)

Publication date: 2021-10-06
Reference number: LI27.57-P-053496

ECO START/STOP INOPERATIVE, FAULT CODE P0944 IN TRANSMISSION CONTROL UNIT

TECHNICAL SERVICE BULLETIN

Reference Number(s): LI27.57-P-053496 Version 3, Date of Issue: October 06, 2021

MERCEDES-BENZ:	NAG2 FEPlus (722.9) with auxiliary oil pump with code B03 up to transmission sequence number 7.248.200
FUNCTION GROUP:	27.57 - Oil pump
REASON FOR CHANGE:	Removed PTSS case reference

COMPLAINT

ECO start/stop inoperative, fault code P0944 in transmission control unit.

ATTACHMENTS

File	Description
Bild Ruckschlagventil im Wandlergehuause.jpg	Pictures of the valve

CAUSE

Leakage between torque converter housing and auxiliary oil pump.

May affect transmissions with transmission sequence numbers starting with-07-xxx xxx.

REMEDY

Access via fault code P0944; and perform there the following test according to the instructions:

Check the check valve in the torque converter housing (in pressure duct) (see pictures in attachment).

If the check valve is n OK, the torque converter housing and the auxiliary oil pump (component M42) must be replaced. When removing/installing the automatic transmission auxiliary oil pump, observe AR 27.30-P-0651EL.

Important note: After the test/repair, check and correct the oil level in the transmission.

If the fault code is no longer present, perform the following test steps.

Step 1: Check auxiliary oil pump connector and fuse

Step 2: Check supply voltage

Step 3: Check CAN lines

Step 4: Check VGS software and update if necessary, then continue with step 5

Step 5: Visual inspection of check valve; the valve is located in the torque converter housing (see pictures in attachment)

If the check valve is Not Ok, the torque converter housing and the auxiliary oil pump (component M42) must be replaced.

Step 6: Replace auxiliary oil pump

If one step resolves the concern, it is not necessary to continue with the remaining test steps. Exception: After step 4 always perform step 5.

WIS-REFERENCES

Document number	Title	Note
AR27.30-P-0651EL	Remove/install automatic transmission auxiliary oil pump

SYMPTOMS

Power transmission > Automatic transmission > Function > Electrical fault/Fault code

CONTROL UNIT/FAULT CODE

Control unit	Fault text
ETC-Electronic transmission control	0944 - There is an internal fault in component M42 (Electric transmission oil pump). ([VGS3_*](DEF@Start_Stop, not(BAUREIHE@221,BAUMUSTER@095), not(BAUREIHE@221,BAUMUSTER@097), not(BAUREIHE@221,BAUMUSTER@195), not(BAUREIHE@221,BAUMUSTER@197)))
ETC-Electronic transmission control	0944 - There is an internal fault in component M42 (Electric transmission oil pump). ([VGS3_*](DEF@Start_Stop, not(BAUREIHE@221,BAUMUSTER@095), not(BAUREIHE@221,BAUMUSTER@097), not(BAUREIHE@221,BAUMUSTER@195), not(BAUREIHE@221,BAUMUSTER@197)))

OPERATION NUMBERS/DAMAGE CODES

Op. no.

Operation text

Time

Damage code

Note