KC-275

12/23/21, 11:08 AM
Article
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(Back Office Only) Vehicles Equipped With A Turbo
Compound Engine - Report Of Frequent Air
Compressor Cycling. Secondary Air System Air
Pressure Decreases Slowly When Engine Is At Low
Idle - US17+OBD16 And Newer Emissions, Model
Year 2018 And Newer
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Internal Content
NO TURBO COMPOUND ASSEMBLIES SHOULD BE REPLACED FOR A
REPORT OF THIS ISSUE.
1. Verify that there is not an existing issue.
• Air pressure decrease will only be observed when the engine is at
low idle. The symptom will not be present while driving, elevated
engine load, or sitting with the engine off and the ignition turned on.
2. If pressure loss is a concern, the technician can check for other
sources of pressure loss.
2.1. The technician may be instructed to block off individual lines at
the chassis air protection valve to determine if there are leaks present
in any other components or there supply and return lines.
3. If the air loss is pinpointed to the Buffer Valve Unit (BVU) / TC air
supply, no components should be replaced. The symptom is still under
investigation by engineering (as of 9 November 2018).
4. If an eService case is open for the vehicle and the TC Unit is the
component implicated, alert Terry Isley for tracking purposes.
5. If a fix is required to resolve the complaint of noise, a Purge Silencer
should be installed on the air dryer. The silencer part number can be
found in Impact in the Air Dryer section. Use the Large Silencer.
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