Question: I have a 2009 Ford Ranger with the 4-cylinder engine, automatic transmission, two-wheel drive and no A/C. When I park in the garage and turn it off, for about a minute I hear a sound like an owl hoot coming from under the vehicle. It is intermittent and sometimes seems to be associated with my movements as I get out of the vehicle. Any thoughts?
Answer: No A/C? A modern vehicle without air conditioning is a real rarity — unless of course it has failed! On a used car lot it would be a “lot queen” — difficult to sell.
The “hoot” sound is likely vacuum bleeding down from something. Primary suspects are the vacuum brake booster and check valve, the HVAC vacuum system. Less likely are emissions-related vacuum components including the EGR vacuum regulator solenoid, vacuum vent valve and manifold pressure/vacuum sensor.
You might be able to pinpoint the source yourself with these two simple tests. After shutting down the engine, wait for the noise to stop, then apply the brake pedal. There should be a “reserve” of vacuum in the brake booster to give you several power-assisted brake applications before the vacuum is “used up” and the pedal gets very hard. If there is no power assist on your first application after the noise has stopped, the leak is likely in the brake booster or check valve. This conceivably could cause a safety issue with a lack of power assist under certain driving situations.
Try moving the HVAC controls from floor to dash after shutting the engine off while the sound is happening. Does this change the sound? If so, the HVAC vacuum reservoir or one of the vacuum motors or controls might be leaking. This is not a safety issue.
Paul Brand, author of “How to Repair Your Car,” is an automotive troubleshooter, driving instructor and former race-car driver.