KC-478 Service Bulletin/Repair Instructions

1/31/22, 6:25 PM
Article
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Variable Geometry Turbocharger ( VGT

) Function Test ( 2551-08-03-02 ), OBD13 Model

Year ( MY ) 2014 And Newer
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Internal Content
Overview

The VGT Function Test has been improved to provide an accurate

graphical representation of turbo position during a sweep test.

Changes that have been made include:

2551-08-03-02 Variable Geometry Turbocharger Function test is

replacing the sector gear gauge tool as the primary method of

VGT diagnosis with more accuracy and less discrepancy.

VGT actuator motor effort has been removed from the

operation because it was resulting in misdiagnosis of the

turbocharger.

A plot of Variable Geometry Turbocharger position (black) and

error / status codes from Variable Geometry Turbocharger ( VGT

) / Smart Remote Actuator ( SRA ) (blue) has been added to the

operation for diagnosis.
Test Information

When performing the test:

Use the Step Test under option A for analysis. The step test is a

sweep of the VGT mechanism from open-close-open that takes

approximately 10 seconds. The graph must be manually

evaluated to determine a pass on the Step Test. Do not rely on

the green check mark status to determine a pass. The following

linked videos use a cutaway to illustrate what is happening

during the Step Test:
Actuator view End view Side view

; Live UI

https://volvo-trkna-prod1.pegacloud.net/prweb/PRAuth/app/VolvoKM_/iNPUIKpeinqPJi2G0hH930k43USdE1gb*/!TABTHREAD5?pyActivity=%40basec…
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Do not use the Full Stroke Test for VGT analysis as it is currently

under revision.

The Step Test can be repeated multiple times and at any

temperature that there is believed to be a problem.
See the image below for more information:
Interpreting Results:

Example 1 – Normal function turbocharger

Actuator closes to 0 - 5% during the step test AND

Status code from the VGT / SRA equals 0 or 7

No further troubleshooting is required, no component

replacement is required.
; Live UI

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Example 2 – Turbocharger actuator is unable to close to 0 - 5%

Symptom: VGT Actuator is unable to close to 0 - 5% during the

step test OR

Status code from the VGT / SRA changes from 7 - Test

Mode to 3 - Slow or Unable to Close
Result: Requires further troubleshooting to determine if the

actuator or the turbocharger is the defective component.

Dismount the actuator from the turbocharger and repeat the

Step Test with the actuator free. If the test again fails replace

only the actuator. If the actuator test passes, replace the

complete turbocharger.
; Live UI

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Example 3 – Turbocharger actuator is unable to close to 0 - 5%

Symptom: Turbo actuator is unable to close to 0 - 5% during the

Step Test.

Note: In this example, the status code from the VGT / SRA

does not change from 7 - Test Mode
Result: Requires further troubleshooting to determine if the

actuator or the turbocharger is the defective component.

Dismount the actuator from the turbocharger and repeat the

Step Test with the actuator free. If the test again fails replace

only the actuator. If the actuator test passes, replace the

complete turbocharger.

Note: This is a problem that will typically cause parked

regeneration failure.
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