Some 2016-2017 ATS, CTS, CT6, Camaro; 2017 LaCrosse, XT5 and Acadia models equipped with the 3.0L V6 engine (RPO LGW) or 3.6L V6 engine (RPO LGX) may have a hollow knocking or tapping sound coming from the engine compartment when the engine is hot. The sound may be due to the operation of the mechanical vacuum pump for the brake system. The sound does not affect the ability of the vacuum pump to supply vacuum to the brake booster or the longevity of the vacuum pump.
If the sound is heard coming from the engine compartment, start the engine and let it idle until the oil temperature reaches 208°F (98°C).
If the sound is present, pump the brakes 3–5 times to check if the sound goes away. If the sound stops, it will return a short time later. The sound occurs when the brake booster system is at equilibrium (fully drawn down). Pumping the brakes requires the vacuum pump to create more vacuum to compensate.
If the sound goes away when applying the brakes, replace the engine oil pump. (Fig. 11) The mechanical vacuum pump is part of the oil pump assembly inside the oil pan and is the source of vacuum for the brake system.
Fig. 11
– Thanks to Bryan Salisbury
OK thank you,
Dean
The sound does not affect the operation of the vacuum pump. However, if the sound is a customer concern, replace the engine oil pump after completing the proper diagnosis. Refer to Bulletin #18-NA-337 for more information.
To whom it may concern,
I and several others have read this article and feel it is contradictory, the end of the first paragraph seems to say that the noise is normal and will not effect operation and the third paragraph explains why the pump makes the noise. The last paragraph seems to imply the noise is not normal and the pump should be replaced. Could you please clarify .