Diagnostic Aids
If the drive belt repeatedly falls off the drive belt pulleys, this is because of pulley misalignment.
An extra load that is quickly applied or released by an accessory drive component may cause the drive belt to fall off the pulleys. Verify the accessory drive components operate correctly.
If the drive belt is the incorrect length, the drive belt tensioner may not keep the correct tension on the drive belt.
Test Description
The numbers below refer to the step numbers 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 drive belt may have been damaged, which caused the drive belt to fall off. Inspect the belt for cuts, tears, sections of ribs missing, or damaged belt plies.
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Misalignment of the pulleys may be caused from incorrect mounting of the accessory drive component, incorrect installation of the accessory drive component pulley, or the pulley bent inward or outward from a previous repair. Test for a misaligned pulley using a straight edge in the pulley grooves across 2 or 3 pulleys. If a misaligned pulley is found, refer to that accessory drive component for the correct installation procedure of that pulley.
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Inspecting the pulleys for being bent should include inspecting for a dent or other damage to the pulleys that may prevent the drive belt from not seating correctly in all of 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 let the drive belt fall off.
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Inspecting the fasteners can address the possibility that a wrong bolt, nut, spacer, or washer was installed. Missing, loose, or wrong fasteners, may cause pulley misalignment due to the bracket moving under load. Over tightening the fasteners may cause misalignment of the accessory drive component bracket.
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 | |
2 | Inspect for a damaged drive belt. Did you find the condition? | 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 |
4 | Inspect for misalignment of the pulleys. Did you find and repair the condition? | Go to Step 12 | Go to Step 5 |
5 | Inspect for a bent or dented pulley. Did you find and repair the condition? | Go to Step 12 | Go to Step 6 |
6 | Inspect for a bent or cracked bracket. Did you find and repair the condition? | Go to Step 12 | Go to Step 7 |
7 | Inspect for incorrect, loose or missing fasteners. Did you find incorrect, loose or missing fasteners? | Go to Step 8 | Go to Step 9 |
8 |
Notice: Refer to Fastener Notice in the Preface section. Does the drive belt continue to fall off? | Go to Step 9 | System OK |
9 | Test the drive belt tensioner for operating correctly. 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 a failed drive belt idler and drive belt tensioner pulley bearings. Did you find and repair the condition? | Go to Step 12 | Go to Diagnostic Aids |
12 | Operate the system in order to verify the repair. Did you correct the condition? | System OK | Go to Step 2 |
