Pinpoint Test F: Can Communications Bus Fault

WARNING: This page is about a different car, the 2006 Mercury Mariner and 2006 Ford Escape. However, it is still accessible from the selected car via links, so may be relevant.

NOTE: Conduct Steps 1 through 7 outlined in Inspection and Verification prior to performing this test.

F1 CHECK FOR DTCs U1900, U0100 AND U0121 SET TOGETHER
- Refer to the results of the 4WD control module self-test.
- Are DTCs U1900, U0100 and U0121 set together?
Yes : REFER to MODULE COMMUNICATIONS NETWORK to continue diagnosis of the communications network.

No : GO to F2.
F2 CHECK FOR DTC U0100
- Refer to the results of the 4WD control module self-test.
- Is DTC U0100 set, but not U1900?
Yes : The PCM is not sending any data to the 4WD control module. REFER to the INTRODUCTION - GASOLINE article or INTRODUCTION -- HYBRID ESCAPE & HYBRID MARINER article for additional PCM diagnosis.

No : GO to F3.
F3 CHECK FOR DTC U0121
- Refer to the results of the 4WD control module self-test.
- Is DTC U0121 set, but not U1900?
Yes : The ABS module is not sending any data to the 4WD control module. REFER to VEHICLE DYNAMIC SYSTEMS for additional ABS diagnosis.

No : GO to F4.
F4 CHECK FOR CORRECT 4WD CONTROL MODULE OPERATION
- Disconnect the 4WD control module.
- Check for:
  - corrosion.
  - pushed-out pins.
- Connect the 4WD control module and make sure it seats correctly.
- Operate the system and determine if the concern is still present.
- Is the concern still present?
Yes : INSTALL a new 4WD control module. REFER to FOUR WHEEL DRIVE (4WD) CONTROL MODULE in this article. CLEAR the DTCs. REPEAT the self-test.

No : The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector. CLEAR the DTCs. REPEAT the self-test.