Drive belt jumping out and increased wear, diagnosis (A20NFT/LHU)
| Drive belt jumping out and increased wear, diagnosis (A20NFT/LHU) |
| Diagnostic tools |
If the drive belt falls off the drive belt pulleys repeatedly then this is because the pulleys are incorrectly aligned.
An extra load that is added suddenly and which is triggered by an accessory drive component may cause the drive belt to fall off the pulleys. Check that the accessory drive components are working correctly.
If the drive belt is the incorrect length then the drive belt tensioner cannot keep the drive belt tensioned correctly.
Heavy wear on the drive belt is normally caused by incorrect fitting or incorrect belt for the application.
A small misalignment of the drive belt pulleys does not lead to heavy wear, but will probably lead to the drive belt being noisy or falling off.
A significant misalignment of the drive belt pulleys leads to heavy wear but may also lead to the drive belt falling off.
| Test description |
The figures below refer to the steps in the diagnostic table.
2
This check is intended to verify drive belt condition. The drive belt may have been damaged when it fell off. The drive belt may have been damaged which led to the drive belt falling off. Check the belts for cuts, tearing, missing flanges or damaged belt layers.
4
Misaligned pulleys can be caused by the incorrect installation of accessory drive components, incorrect installation of an accessory drive component pulley or the pulley being bent inwards or outwards in a previous repair. Test if a pulley is misaligned with the help of a straightening plate in the pulley grooves over two or three pulleys. If a misaligned pulley is identified, see the related accessory drive component for the correct installation procedure for the pulley.
5
When checking whether the pulley is bent you should also check for any dents or other damage to the pulleys. This could cause the drive belt not to be seated correctly in all the grooves or on the smooth surface of a pulley when the rear of the belt is used to drive the pulley.
6
Brackets for accessory drive components that are bent or cracked lead to the drive belt falling off.
7
Checking the fasteners may exclude the possibility that the incorrect screw, nut, spacer or washer has been fitted. Missing, loose or incorrect fasteners may result in misalignment of pulleys because the bracket moves under load. The over-tightening of fasteners may lead to misalignment of the accessory component bracket.
13
The check is used to verify that the drive belt is correctly fitted on all drive belt pulleys. Wear on the drive belt may be caused by incorrect positioning of the drive belt on a groove on the pulley.
14
Fitting a drive belt that is too wide or too narrow leads to wear on the drive belt. Drive belt flanges must match the grooves on all the pulleys.
15
This check is used to verify that the drive belt is not in contact with any parts of the engine or body when the engine is running. There should be sufficient play when the load on the drive belt's accessory component varies. The drive belt must not come into contact with an engine or body component during acceleration.
| Stage | Event | Yes | No | ||||||
| DEFINITION: The drive belt falls off the pulleys or may not run correctly on the pulleys. DEFINITION: Wear on the drive belt's outer flanges due to the drive belt being fitted incorrectly. | |||||||||
| 1 | Did you go through the Symptoms for drive belt, and did you carry out the necessary checks? | Go to Step 2 | Go to "Symptoms - Engine mechanics" | ||||||
| 2 | If the diagnosis shows heavy wear, proceed to Step 13. If the diagnosis shows that the drive belt falls off then check for damage to the drive belt. Did you identify the condition? | Go to Step 3 | Go to Step 4 | ||||||
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3
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Fit a new drive belt. See Drive belt, auxiliaries (poly-V) . Does the drive belt continue to fall off? | Go to Step 4 | System OK | ||||||
| 4 | Check whether the pulleys are misaligned. Did you identify and repair the condition? | Go to Step 12 | Go to Step 5 | ||||||
| 5 | Check whether a pulley is bent or dented. Did you identify and repair the condition? | Go to Step 12 | Go to Step 6 | ||||||
| 6 | Check whether a bracket is bent or dented. Did you identify and repair the condition? | Go to Step 12 | Go to Step 7 | ||||||
| 7 | Check for defective, loose or missing fasteners. Did you identify loose or missing fasteners? | Go to Step 8 | Go to Step 9 | ||||||
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8
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Does the drive belt continue to fall off? |
Go to Step 9 | System OK | ||||||
|
9
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Test that the drive belt tensioner is working correctly. See Drive belt, auxiliaries (poly-V) . Is the drive belt tensioner working correctly? | Go to Step 11 | Go to Step 10 | ||||||
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10
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Replace the drive belt tensioner. See Drive belt, auxiliaries (poly-V) . Does the drive belt continue to fall off? | Go to Step 11 | System OK | ||||||
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11
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Check whether the bearings for the drive belt's intermediate pulleys and tension pulleys are damaged. Did you identify and repair the condition? | Go to Step 12 | Go to Diagnostic tools | ||||||
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12
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Use the system to check the repair. Did you correct the condition? | System OK | Go to Step 2 | ||||||
| 13 | Check that the drive belt is correctly fitted. See Drive belt, auxiliaries (poly-V) . Did you identify this condition? | Go to Step 16 | Go to Step 14 | ||||||
| 14 | Check that the drive belt is correct. Did you identify this condition? | Go to Step 16 | Go to Step 15 | ||||||
| 15 | Check whether the drive belt is rubbing against a bracket, a hose or a cable kit. Did you identify and repair the condition? | Go to Step 17 | Go to Diagnostic tools | ||||||
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16
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Replace the drive belt. See Drive belt, auxiliaries (poly-V) . Have you completed the replacement? | Go to Step 17 | - | ||||||
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17
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Use the system to check the repair. Did you correct the condition? | System OK | - | ||||||
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