| Cause | Correction | |
| Drive belt squeal, insufficient tension or abnormally high loading |
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Check the tensioner and inspect the drive belt. Make sure water pump, tensioner pulley, fan hub and alternator turn freely. |
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Check the tension of accessory drive belts. Make sure the accessories turn freely. |
| Intake air or exhaust leaks |
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Refer to Troubleshooting Logic for excessive exhaust smoke. |
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| Excessive valve lash |
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Adjust valves. Make sure the push rods are not bent or the rocker levers are not severely worn. |
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| Turbocharger noise |
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Check turbocharger impeller and turbine wheel for housing contact. |
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| Gear train noise |
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Visually inspect and measure gear backlash. Replace gears as required. |
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| Power function knock |
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Check/replace rod and main bearings. |