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Part 3. Functional Inspection

The final part of the entire smog test process is the functional inspection. The functional inspection is mainly conducted by the smog technician, and is hands-on. The smog technician will insure proper operation of the following emissions components and systems.

A. Engine Ignition Timing
B. Check Engine Light
C. Gas Cap & Filler Neck
D. Exhaust Recirculation Valve (EGR)
E. Fuel EVAP Test (LPFET)

A. Engine Ignition TimingYour vehicle's engine ignition timing will be inspected during the smog test. The smog technician will insure ignition timing is set properly, and the system is supplying electric current to the sparkplugs at the correct intervals.

Spark, 15,000 to 20,000 volts, is created at the engine's ignition coil. Electricity is delivered to the coil, a spark is generated, then sent to the distributor. It is the distributors responsibility to route the spark to the correct spark plug, at the correct time. The timing inspection will insure the distributor is sending spark plug energy at the exact moment required for optimum air/fuel combustion. Adjusting a vehicle's ignition timing is performed by rotating the distributor clockwise or counterclockwise direction as needed.

Failed Ignition Timing: Engine ignition timing is measured in degrees. An ignition timing failure for example; ignition timing is required to be set at 15 degrees Before Top Dead Center (BTDC) and instead is set to 10 After Top Dead Center (ATDC). This fault will cause a functional failure, as well as increase Hydrocarbon (HC) emissions. California's emissions standards allow timing to be up to 3 degrees +/- off the manufacturer's required setting; resetting is recommend. One or two degrees off will not cause your vehicle to fail the ignition timing inspection.

Electronic Ignition Timing: Some late model vehicles may not have an ignition distributor, and therefore no timing adjustment or testing of the ignition system is required. On these engines, timing is controlled electronically by the Engine Control Unit, also known as the ECU, and the camshaft sensor and/or crankshaft sensor.

Both the crankshaft and camshaft sensors send vital data to the ECU indicating the position of the engine pistons, thus allowing the ECU to send spark to the proper cylinder at the exact moment fuel and air mixture is at it's optimum pressurization.

Any electronic ignition timing fault will automatically illuminate the check engine light, service engine soon light, or malfunction indictor lamp.

B. Check Engine Light (MIL)My car's check engine light is on. Will I fail the smog test? Contrary to public belief, the check engine light, malfunction indicator lamp, or service engine soon light being constantly illuminated is an automatic smog failure. Vehicle manufacturers have placed the check engine light inside the passenger compartment to inform the driver that there has been an engine or drivetrain malfunction.

Often a vehicle's check engine light can be illuminated but the owner not notice any driveability concerns. Once the check engine light, malfunction indicator lamp (MIL), service engine soon lamp turns on, the engine's ECU (emissions control unit - may also be referred to as engine control unit or engine control computer) begins to operate under pre-programmed data rather then of real-time.

In other words, the computer has sensed an error from an emissions component, and replaced the data from the component with data from it's memory.

How is the Check Engine Light tested? During the emissions inspection the check engine light is tested two ways. The first is conducted by the smog technician, and the second by the smog machine. The smog machine test only applies to vehicles 1996 model and newer. We will explain why later.

Part 1. OBD I & II "Check Engine Light" Test: During the smog technician's functional test, he/she will be looking for a constant or intermediate illuminated check engine light, malfunction indicator lamp, or service engine soon light. By the way... all three of these lights are similar in terms of being engine emissions trouble lights. Your vehicle is equipped with only one of these types of lights. Ford Motor Company will typically choose to use a service engine soon light instead of a check engine light. Honda chooses to use the check engine light. Each manufacturer has a preference. They all do the same thing.

The smog technician or mechanic will be looking for an illuminated check engine light during the smog inspection. Any time the check engine light is illuminated while the engine is running causes an automatic smog test failure. The only time the technician wants to see the check engine light on is when the ignition is in the ON position, and engine not running.

If the check engine light is not illuminated while the ignition is in ON position and engine off, this too causes an immediate smog check failure. The fact that the check engine light does not turn on during ignition ON may be due to a defective emissions control computer and/or a defective light bulb (Check Engine Light Lamp - 12v). Both are failures.

During the last phase of the smog test, the technician will be asked to enter your vehicle's check engine light visual results. He/She will enter the data as noted. Check engine light OFF or ON. That alone will determine your vehicle's success in passing the test or not.

Part 2. OBDII "Check Engine" Test: The second part of Check Engine Light test applies to 1996 or newer cars, trucks, SUVs, vans, and RVs only. These vehicles are equipped with an On Board Diagnostics (OBD II) system and input/output data link connecter (DLC). During the smog test your vehicle will be attached to the smog machine via it's OBD II DLC link connecter. The OBD II link will relay all "Check Engine" conditions along with stored trouble codes within it's database to the smog machine while the vehicle is being tested. If any trouble codes are present which caused the check engine light to illuminate either regularly or intermittently, the data will be sent to the smog machine via the data link connecter cable and the vehicle will fail the smog inspection.

The OBD II diagnostic system is designed to monitor all aspects of an engine's emissions control system, and report this information to a central database within the ECU (computer). This information is processed and checked against the computers pre-determined values for various inputs levels and performance patterns. If any problems are found, the computer will determine whether to alert the driver or not. If a decision has been made to alert the driver of an emissions problem, the "Check Engine" or "Engine Malfunction" light will illuminate on the vehicle's dashboard. In more serious emission conditions the computer may even begin to rapidly flash the "Check Engine/Malfunction" light indicating to the driver, that the vehicle needs immediate diagnosis/repair attention.

Part 3. OBDII "Readiness Flags" Test: Your 1996 and newer car, truck, van, SUV, or motorhome will not pass the smog test if certain "readiness flags" are not set. Some "check engine" related failures don't illuminate the check engine light, but do cause smog check failures. These faults are referred to as "readiness flag" faults. Readiness flags indicate that certain emissions systems which the OBD II computer has been monitoring have passed internal self monitoring tests, indicating that those systems are working properly. If the smog machine detects that there are certain readiness flags which have not set, the data will be relayed to the smog machine and your vehicle will fail the smog test.

In order to set all the proper Readiness Flags the OBDII system must complete at least one good drive cycle (in some cases two or three). A good drive cycle is a sequence of passing internal tests which the OBDII computer runs while your vehicle is being driven. This insures all emissions systems are functioning properly. A drive cycle usually requires one to two weeks of ordinary everyday driving.

Readiness flag failures are often seen on vehicles which have had recent repairs requiring disconnecting of the battery, and/or the emissions computer. Disconnection of power to the ECU resets all readiness flags. These vehicles will need to be driven in order to reset the required flags.