Engine Cold/Knock/Tick Noise (Clean Deposits)

This bulletin is being revised to change models. Please discard Corporate Bulletin Number 99-06-01-010B (Section 06 - Engine).

Some customers may comment about a tick/knock noise, sometimes described as an upper engine ticking noise or a deep low knock that sounds similar to a main bearing knock. This noise is more often heard during engine start up after a long cold soak condition and may or may not diminish as the engine reaches normal operating temperature. The knock may appear to be the loudest at the exhaust manifolds on either side or both. This noise does not change when disconnecting spark plug wires, or individually disabling the fuel injectors. As a general rule, the source of this noise cannot be determined.

The source of this noise may be carbon deposits in the engine combustion chambers.

Before considering major engine repairs, the technician should perform the following procedure to clean carbon from the engine combustion chambers.

Notice: This procedure must be strictly followed. If this procedure is not strictly adhered to, hydrostatic lock may result, causing severe engine damage.

1. Obtain one can of GM Top Engine Cleaner (TEC) P/N 1052626 (in Canada, use P/N 993026).
2. Start the engine and bring the engine coolant temperature above the 200-degree mark on the instrument panel gauge, or approximately 220°F (104°C) on the Tech 2 scan tool.

Important: Do not raise the engine speed above normal idle.

3. With the engine idling, disconnect the PCV hose from the PCV valve and slowly spray the GM Top Engine Cleaner (TEC) into the end of the hose.
4. Raise the engine speed to approximately 2000 RPM until you see a cloud of white smoke coming out of the exhaust pipe, then shut off the engine.
5. Let the vehicle sit for at least 20 minutes, preferably overnight. This allows time for the GM Top Engine Cleaner (TEC) to act on the carbon deposits.
6. Once the soak period has been completed, start the engine and proceed to remove the remainder of the GM Top Engine Cleaner (TEC) from the engine by increasing the engine speed to 2000 RPM until the white smoke has diminished.
7. If the noise is still present after performing this procedure, continue with traditional engine knock noise diagnosis as outlined in the applicable Service Manual.

Parts are currently available from GMSPO.

For vehicles repaired under warranty, use: