Diagnostic Aids
If the drive belt repeatedly falls off the accessory drive pulley(s), this may be caused by a pulley misalignment.
An extra load that is quickly applied or released by an accessory drive component may cause the drive belt to fall off. Verify that the accessory drive component(s) operating properly.
If the drive belt is the incorrect length, the drive belt tensioner may not maintain the proper tension on the drive belt.
Test Description
The numbers below refer to the steps on the diagnostic table.
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This inspection is to verify the condition of the drive belt. Damage may have occurred to the drive belt when the drive belt fell off the pulley. Inspect the drive belt for cuts, tears, sections of ribs missing, or damaged belt plys.
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Misalignment of the accessory drive pulley(s) may be caused from improper mounting or incorrect installation of a accessory drive component, or the pulley mat be bent inward or outward from a previous repair. Test for a misaligned pulley using a straight edge in the pulley grooves across two or three pulleys. If a misaligned pulley is found refer to that accessory drive component for the proper removal and installation procedure of that pulley.
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Inspection of the accessory drive pulley(s) should include inspecting for bends, dents, or other damage that would prevent the drive belt from seating properly in the pulley grooves or on the smooth surface of a pulley when the back side of the belt is used to drive the pulley.
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Accessory drive component brackets that are bent or cracked will also cause the drive belt to fall off.
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Inspection of the fasteners can eliminate the possibility that a incorrect bolt, nut , spacer, or washer was installed. Missing, loose, or incorrect fasteners may cause pulley misalignment from the accessory drive bracket(s) moving under load. Over tightening the fasteners may cause misalignment of the accessory component bracket(s).
Step | Action | Yes | No |
|---|---|---|---|
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Notice: Refer to Belt Dressing Notice in the Preface section. DEFINITION: The drive belt falls off the pulleys or may not ride correctly on the pulleys. | |||
1 | Did you review the Symptoms - Engine Mechanical diagnostic information, and perform the necessary inspections? | Go to Step 2 | |
Inspect for a damaged drive belt. Was a damaged drive belt found? | Go to Step 3 | Go to Step 4 | |
3 | Install a new drive belt. Refer to Drive Belt Replacement . Does the drive belt continue to fall off? | Go to Step 4 | System OK |
Inspect for misaligned accessory drive pulley(s). Did you find and correct the condition? | Go to Step 12 | Go to Step 5 | |
Inspect for a bent or dented accessory drive pulley(s). Did you find and correct the condition? | Go to Step 12 | Go to Step 6 | |
Inspect for a bent or a cracked accessory drive bracket(s). Did you find and correct the condition? | Go to Step 12 | Go to Step 7 | |
Inspect for incorrect, loose, and/or missing fasteners. Were there any incorrect, loose, and/or missing fasteners? | Go to Step 8 | Go to Step 9 | |
8 |
Does the drive belt continue to fall off? | Go to Step 9 | System OK |
9 | Test the drive belt tensioner for correct operation. Refer to Drive Belt Tensioner Diagnosis . Does the drive belt tensioner operate correctly? | Go to Step 11 | Go to Step 10 |
10 | Replace the drive belt tensioner. Refer to Drive Belt Tensioner Replacement . Does the drive belt continue to fall off? | Go to Step 11 | System OK |
11 | Inspect for failed drive belt idler and/or drive belt tensioner pulley(s) bearings. Did you find and correct the condition? | Go to Step 12 | -- |
12 | Run the engine in order to verify the repair. Does the drive belt still fall off? | -- | System OK |
