Isuzu KB P190. Manual - part 708

Engine Mechanical – V6

Page 6A1–55

Drive Belt Squeal

Definition

Accessory drive belt squealing can be defined as a loud screeching noise caused by a slipping drive belt. Belt squeal is
unusual in multi-rib belts. Drive belt squeal generally occurs when a heavy load is applied to the drive belt, such as an
air-conditioning compressor engagement, snapping the throttle, seized pulley or a faulty accessory drive component.

Diagnostic Aids

If the noise is intermittent, confirm the accessory drive components by varying their loads, making sure they are operated
to their maximum capacity. An overcharged A/C system, restrictions in the power steering pressure circuit or a faulty
generator or coolant pump are likely causes of accessory drive belt squeal.

A loose or incorrectly installed body component, suspension component or other item may be the cause of the noise.

Test Description

The numbers below refer to steps in the diagnostic table.

The noise may not be engine related. This step is to confirm the engine is making the noise. If the engine is not
making the noise, do not proceed further with this diagnostic procedure.

The noise may be an internal engine noise. Removing the drive belt and operating the engine briefly will confirm
whether or not the noise is related to the drive belt.

CAUTION

When running the engine with the accessory
drive belt removed, the coolant pump will not
be operating and the engine may overheat if
left unsupervised even for a short period.

N O T E

There may also be a number of DTCs set when
running the engine with the accessory drive belt
removed.

Confirms an accessory drive component does not have a seized bearing. With the belt removed, test the bearings
in the accessory drive components spin free and smooth.

Confirms the drive belt tensioner is operating correctly. If the drive belt tensioner is not operating correctly, drive
belt tension will not be maintained, resulting in a belt squealing noise

Confirms the belt is not too long, which would prevent the tensioner from working as intended. Also, if an
excessively long belt has been fitted, it may also be routed incorrectly and may be turning an accessory drive
component in the wrong direction.

Misalignment of the pulleys may be caused by one of the following:
•

Incorrect mounting of an accessory drive component,

•

Incorrect installation of an accessory drive pulley or,

•

Bent or damaged pulley.

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 the relevant component service information for the correct installation and removal procedures.

This test is to confirm the pulleys are the correct diameter and/or width. Using a known good vehicle, compare the
pulley sizes.

Diagnostic Table

Step Action

Yes

Did you review the information provided in 2.2 Symptoms, and
perform the required inspections.

Go to Step 2

Go to

2.2 Symptoms

Confirm the customer complaint. Is there a squealing noise?

Go to Step 3

Refer to Diagnostic
Aids in this Section

Engine Mechanical – V6

Page 6A1–56

Step Action

Yes

Remove the drive belt, refer to 3.5 Accessory Drive Belt.

Operate the engine for no more than 40 seconds.

Does the squealing noise still exist?

Accessory drive

system OK.

Go to 2.2

Symptoms, and

restart the diagnosis

of the noise

Go to Step 4

Inspect the accessory drive components for a seized bearing and
general malfunctions.

Did you find and correct any seized bearings or general malfunctions
in the accessory drive system?

Go to Step 9

Go to Step 5

Test the accessory drive belt tensioner for correct operation, refer to
Accessory Drive Belt Tensioner Diagnosis.

Did you find and repair any problems with the tensioner?

Go to Step 9

Go to Step 6

Inspect the accessory drive belt is the correct length, refer to 3.5
Accessory Drive Belt.

Did you find and repair any problems with the drive belt length?

Go to Step 9

Go to Step 7

Inspect the accessory drive pulleys for misalignment.

Did you find and correct any misaligned accessory drive pulleys?

Go to Step 9

Go to Step 8

Check the accessory drive pulleys are the correct size.

Did you find and replace any incorrect pulleys?

Go to Step 9

Refer to Diagnostic
Aids in this Section

Reinstall the accessory drive belt and operate the system to confirm
the repair.

Did you correct the squeal noise?

Accessory drive

system OK

Go to 2.2

Symptoms, and

restart the diagnosis

Engine Mechanical – V6

Page 6A1–57

Drive Belt Whine

Definition

Accessory drive belt whine can be defined as a high-pitched continuous noise that is most likely to be caused by a failed
bearing in one of the accessory drive components.

Diagnostic Aids

The drive belts themselves will not cause a whine. If the noise is intermittent, confirm the accessory drive components by
varying their loads, making sure they are operated to their maximum capacity. An overcharged A/C system, restrictions
in the power steering pressure circuit or a faulty generator or coolant pump are likely causes of accessory drive belt
whine.

Test Description

The numbers below refer to steps in the diagnostic table.

The noise may be an internal engine noise. Removing the drive belt and operating the engine briefly will confirm
whether or not the noise is related to the drive belt.

CAUTION

When running the engine with the accessory
drive belt removed, the coolant pump will not
be operating and the engine may overheat if
left unsupervised even for a short period.

N O T E

There may also be a number of DTCs set when
running the engine with the accessory drive belt
removed.

The inspection of bearings should include the following accessory drive components:
•

drive belt tensioners,

•

drive belt idlers,

•

generator,

•

power steering pump,

•

coolant pump, and

•

A/C compressor.

The drive belt may need to be installed and the accessory drive components operated separately, at varying loads
to confirm the location of the faulty bearing, refer to the relevant Sections for component inspection and repair
procedures.

Diagnostic Table

Step Action

Yes

Did you review the information provided in 2.2 Symptoms, and
perform the required inspections.

Go to Step 2

Go to

2.2 Symptoms

Confirm the customer complaint. Is there a whining noise?

Go to Step 3

Refer to Diagnostic
Aids in this Section

Remove the drive belt, refer to 3.5 Accessory Drive Belt.

Operate the engine for no more than 40 seconds.

Does the whining noise still exist?

Accessory drive

system OK

Go to 2.2

Symptoms, and

restart the diagnosis

Go to Step 4

Inspect the accessory drive components for a faulty or seized
bearings and general malfunctions.

Did you find and correct any faulty/seized bearings or general
malfunctions in the accessory drive system?

Go to Step 5

Refer to Diagnostic
Aids in this Section

Reinstall the accessory drive belt and operate the system to confirm
the repair.

Did you correct the whine?

Accessory drive

system OK

Go to 2.2

Symptoms, and

restart the diagnosis

Engine Mechanical – V6

Page 6A1–58

Drive Belt Rumble

Definition

Accessory drive belt rumble can be defined as a low pitch tapping, knocking or thumping noise heard at or just above
idle, once per rotation of the drive belt or a specific component. Drive belt rumble is generally caused by one of the
following:
•

pilling or strings in the drive belt grooves,

•

separation of the drive belt, or

•

a damaged or faulty drive belt.

N O T E

Pilling is the small balls (pills) or strings of rubber
in the belt grooves caused by the accumulation of
rubber dust.

Diagnostic Aids

Vibration from the engine may cause a body component or other parts to emit a rumbling noise.

The drive belt may have a condition that cannot be seen or felt. Sometimes the replacement of the belt may be the only
way to confirm the belt is faulty.

If the drive belt has been replaced and the diagnostic table completed, but the rumble is still present only when the drive
belt is installed, an accessory drive component such as the A/C compressor may be the cause. Varying the load to each
accessory drive component in turn, should help isolate which component is causing the noise.

Test Description

The numbers below refer to steps in the diagnostic table.

Confirms the symptom exists at the time of diagnosis. Other vehicle components may be causing the noise.

Confirms the accessory drive belt is the cause of the noise. Drive belt rumbling is often confused with an internal
engine noise due to the similarity in the description. Removing the drive belt and operating the engine briefly will
confirm whether or not the noise is related to the drive belt.

CAUTION

When running the engine with the accessory
drive belt removed, the coolant pump will not
be operating and the engine may overheat if
left unsupervised even for a short period.

N O T E

There may also be a number of DTCs set when
running the engine with the accessory drive belt
removed.

Inspecting the drive belt is to ensure that it is not causing the noise. Small cracks across the ribs of the drive belt
will not cause the noise and are not justification alone to replace the belt. Belt separation can be identified by the
ply of the belt separating and may be seen at the edge of the belt or felt as lumps under the belt.

Small amounts of pilling is a normal condition and is deemed acceptable. When the pilling is severe (33% of the
belt groove depth), the belt does not have a smooth surface to run on and should be replaced.

Diagnostic Table

Step Action

Yes

Did you review the information provided in 2.2 Symptoms, and
perform the required inspections.

Go to Step 2

Go to

2.2 Symptoms

Confirm the customer complaint. Is there a rumbling noise?

Go to Step 3

Refer to Diagnostic
Aids in this Section

Remove the drive belt, refer to 3.5 Accessory Drive Belt.

Operate the engine for no more than 40 seconds.

Does the rumbling noise still exist?

Accessory drive

system OK

Go to 2.2

Symptoms, and

restart the diagnosis

Go to Step 4

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