All Doors Failing to Lock & Unlock From Any Switch

SYMPTOM
* ALL DOORS FAILING TO LOCK & UNLOCK FROM ANY SWITCH

POSSIBLE CAUSES
- No response (CTM) / CCD bus failure
- CTM ground circuit open
- Fuse # 4 defective
- Fuse # 4 open
- Fused B (+) circuit open
- Fused B (+) circuit short to ground
- Door lock driver circuit short to ground
- Door unlock driver circuit short to ground
- CTM defective - lock & unlock function