I have a 2004 6 cyl. trailblazer, auto transmission. When I first start my car, in park, there is a whinning sound under the car that last for approximately one minute and then goes away. When the engine is warm or hot, the whinning will not be there. This will only occure when the car is cold. Also, when I first start the car and immediately turn the engine off, the whinning continues for approximately 10 seconds and then goes away. Any suggestions?

 

By whinning "under the car," do you mean under the hood or underneath the bottom of the vehicle?

I have an '03 with 6 cylinder. In 2007, we had a whinning sound under the hood. It turned out that when first started, the fan clutch was keeping the cooling fan turning full speed (which makes a loud whinning sound). The fan clutch is electronically controlled. After a few minutes, the fan clutch worked normally and the fan no longer turned full speed (loud whirring sound went away). Eventually the fan clutch failed causing the cooling fan to turn full speed all the time (contast loud whirring sound). In 2007 the part alone (fan clutch) was $260 (and another $60 for tool to remove pully bolts).

 

It is hard to tell if the sound is under the hood or bottom of vehicle. The sound does not appear to be coming from the hood area. I am pretty sure the sound is not coming from the cooling fan. Once the engine has stopped after a cold start, the whining continues for seconds (5-10 sec.). Visually, once the engine has stopped nothing is moving/spinning; fan, pullies, etc. It seems that when the engine heats up, 2-5 minutes, the whining stops. Could it be the starter? Once it disengages, is it possible that it is still spinning for a while?

 

If it was the cooling fan clutch, it would be obvious it is coming from under the hood.

Sorry, not sure what's making your sound.

 

This could be your Secondary Air Injection (SAI) pump. On 2004-2008 TB 6 cyl it is bolted to the frame under the driver side of the vehicle.

The SAI pump runs when you start a cold engine and provides pressure to inject more air into the exhaust manifold to enable more complete combustion of exhaust gases and there minimize pollutants. Once the engine warms some the pump stops running. AND if you shut off the engine before it has warmed the power to the pump is turned off but the pump will take a little while to spin down.

I replaced my pump recently after it had failed. It is an easy job.
BTW: A failed SAI system will bring up a 410 Check Engine Code.

Here's a drawing of the SAI System:


#6 is the Secondary Air Injection pump.
#2 is the Secondary Air Injection Valve.

 

Ear Mountain,

You hit the nail on the head. Sure enough, the whining is coming from that pump. Is the whining an indication that the pump is getting ready to go bad? If the pump does fail while on the road, will this have an immediate effect to the operation of the car? Thanks again for the help.

 

The Secondary Air Injection pump is part of an emission control system. As I mentioned it only runs when the engine is started cold. When running, the pump draws air through a hose attached to the air filter. That filtered air is then sent to the exhaust manifold to provide additional oxygen to aid in the complete burning of some of the exhaust products coming from the cold cylinders. Once the engine warms the pump stops running.

To prevent exhaust gases from back flowing to the pump there is a check valve on the exhaust manifold. When the pump is running, the check valve is open so air can enter the exhaust manifold. The check valve closes when the pump is off so exhaust cannot back flow into the hoses used by the SAI Pump.

In addition to the pump failing, the check valve can fail. In fact it seems the failure of the check valve is more common to pump failure. The check valve can either stick open or closed. If the check valve remains open when the engine is running exhaust gases will back flow into the hoses. Moisture in the exhaust will condense and settle in the lowest part of the hoses which happens to be the pump. This will eventually damage the pump and cause its failure.

In your case the first thing I'd check is the hose from the pump to the check valve. It is easy to disconnect at the pump. It's the outlet hose from the pump. If any water has accumulated in that hose it is a sign that the system is failing. Most likely then the check valve is stuck open.

If the check valve is stuck open or closed you should get a "Check Engine" light on your dash and the error code (when read) will be 0410 (Secondary Air Injection System Failure). The error code may not show if the check valve failure is real intermittent.

If you have not gotten the error code and there is no water in the hose I'd suspect that the valve is working.

A whining in the pump with no water in the hose might indicate a failing pump. The pump is completely enclosed and cannot be serviced. Your only remedy is replacement. If the pump does not provide enough pressure or if the pump fails completely you will again get the 0410 error code.

The price for the pump can be up to $200 and the check valve up to $125. Both can easily be replaced yourself to save labor costs. The only difficulty is that the pump is hard to reach unless you can raise the vehicle some.

To answer your question:
While on the road the pump does not run so, no, there will be no immediate effect on the operation of the vehicle. Cold starts with a pump not working will result greater harmful emissions and this could impact your catalytic converter over time but I'm not sure about that one. Even with a failed pump and stuck check valve your vehicle will start and run, seemingly like normal, except that you should eventually get that 0410 error code on the check engine light.

Also take a look at This Thread and This Thread on the SAI Pump.