DR. Gizmo Part IV Page 2

January 3, 2010

2008 Hyundai Santa Fe FWD 4-door Auto SE Angular Rear Exterior View

Vehicle Fails Emission Test Due To Fuel Vapor Leak 

Question 3

The check engine light is on in my 2000 Chevrolet Blazer with a 4.3-liter V-6 engine.  My truck has 147,000 miles.  It runs as good as new but it failed the state exhaust emissions test because the light is on.

After the smog test, I took the truck to an auto supply store where a person ran tests on the computer.  His tester found code po442.  He said that the code indicates a leaky gas tank.  When I got home, I checked the gas tank for leaks.  It is rusty, but I dont see any leaks.  Also, I dont smell any gasoline fumes.

What is causing the check engine light to turn on?  A.T.O., email.

Answer 3

The code that the auto parts store person read from his test equipment indicates a small evaporative emissions leak.  Your vehicle is designed to prevent gasoline vapors from escaping into the air.  The fuel system is sealed.  Sometimes when something such as a gas cap fails, sensors in the fuel system send a signal to the powertrain computer that there is a vaporous leak and that the fuel system is no longer sealed.  In turn, the powertrain computer illuminates the check engine light.  Sometimes the check engine light turns on when liquid fuel drips from a leak, but it also turns on when fuel vapors escape.  Since the sensors are extremely sensitive, your nose may not detect any fuel odor at all.

Fixing the trouble might be difficult.  Small vapor leaks are difficult to detect.  Technicians use specialized equipment to locate small leaks.  Troubleshooting a vapor leak can be a time-consuming process that racks up labor charges when a failed $3 rubber seal is the source of the condition.  Let us hope that it does not take long for a technician to pinpoint the leak in your truck.

Its possible a faulty gas cap, failed seal, solenoid, purge valve, fuel hose or rusted fuel tank filler neck is the source of a vapor leak.  A contaminated canister can trigger the engine light, too.  A technician needs to focus on the entire system in order to find the source of the leak.  Once he or she locates it, the repair might take a few minutes.

ABS Warning Light Illuminates In Cold Weather

Question 4

Intermittently, the anti-lock brake warning light turns on in my 2002 Chevrolet Tahoe.  Last winter the light turned on.  When the light is on as I apply the brakes the brake pedal sinks and it feels like truck will not stop.  After I drive a few minutes, the brakes begin to work normally.  This only happens in the morning for the first few minutes of driving on cold days.  During the summer, the light does not turn on and the brakes feel and work fine.  Now that cold weather has returned, the brakes are acting up. 

Whats the problem?  T.L., email

Answer 4

This condition is serious.  Take the vehicle to a repair shop to have the problem corrected before you are involved in a collision.  Leave it overnight so a technician can experience the symptoms in the morning when the truck is cold.

The trouble might be the result of failed wheel speed sensors.  Maybe corrosion or dirt is affecting the air gap between the sensors and tone ring.  Maybe an electrical connection is suffering from moisture or corrosion.

Ask a technician to consider my suggestions when you take your truck to a repair shop.  Dont delay.

Engine Lies Dormant When Ignition Is Turned 

Question 5

Occasionally, my 2005 Chevrolet Colorado with a 3.5-liter engine will not start.  This can happen the first thing in the morning on the initial start of the day or it may happen after I have driven an hour, stop and return to the truck.  When I turn the key to start the engine, nothing happens.  The lights on the dash turn on, but the engine does not make a sound.  If I wait ten minutes or so and try again, the engine usually jumps to life and starts as though nothing is wrong.

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