I'm not sure what year Jeep you have, but there is a TSB concerning service 4WD system light and the lack of a trouble code. You if it applies to your Jeep then you may want to take it in.


tsb_wk_2101406a.pdf

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SUBJECT:
Flash: Erroneous Fault Warning - Service 4WD System Illuminated
OVERVIEW:
This bulletin involves selectively erasing and reprogramming the Final Drive Control
Module (FDCM) with new software.
MODELS:
2005 - 2006 (WK) Grand Cherokee
**2005** - 2006 (WH) Grand Cherokee (International Markets)
2006 (XK) Commander
2006 (XH) Commander (International Markets)
NOTE: This bulletin applies to vehicles equipped with Quadra Trac II (sales code
DHX) or Quadra Drive II (sales code AWB) **and built on or prior to May 19,
2006 (MDH 0519XX)**.
SYMPTOM/CONDITION:
The vehicle operator may describe “Service 4WD System” is illuminated but there is only a
stored Diagnostic Trouble Code (DTC) present or no fault present when the FDCM is
interrogated by a Scan Tool (StarSCAN®).
DIAGNOSIS:
Using StarSCAN® with the appropriate Diagnostic Procedures available in
TechCONNECT, verify all systems are functioning as designed. If DTCs are present
record them on the repair order and repair as necessary before proceeding further with this
bulletin.