Counter Talk – Knowledge Building: 10 Things Consumers Should Know About Emissions Repairs

With the proliferation of inexpensive retail trouble code scanners comes the potential of the misinformed consumer.

Whether one of them arrives at your place of business looking for a DIY solution to a complex driveability problem, or with a failed emissions test report in hand, or shows up at a customer’s shop with a trouble code written on the back of a parking receipt, professing to know exactly what the problem is–there are a few things that he may not understand.

1) Just because a trouble code indicator goes out doesn’t mean the trouble is gone. Intermittent problems are insidious and all too common.

2) An oxygen sensor can be seriously compromised for a long time without triggering the Check Engine light, wasting fuel and maybe even killing a catalytic converter (or two) in the process.

3) Just because a vehicle fails an emissions test one day, and passes one the next, doesn’t mean the testing system is flawed; it means the vehicle’s operation is erratic and in need of repair.

4) Even OBD-II-equipped vehicles cannot diagnose every single fault; just because a light didn’t come on doesn’t mean there wasn’t a problem.

5) Their code scanner is not the same as yours; the multi-faceted capabilities of a professional diagnostic scanner really do help understand the cause of a problem–and that service, and the investment it requires, is reasonable to charge for.

6) You can’t scan for every problem, and a scanner doesn’t tell you every detail of a repair; sometimes the cause can be elsewhere, and the failure or trouble code set by one component is just a consequence of the failure of another component. Diagnosis is a tricky business, even with the right tools.

7) Just because no parts needed replacing doesn’t mean a garage didn’t do anything. Sometimes recalibrating an engine control unit or downloading new control software can solve a problem.

8) Just because the owner’s manual says that spark plugs do not need to be replaced for 160,000 km doesn’t mean they will last that long if they have been exposed to abnormal combustion for an extended period of time.

9) Unlike the old days, computers can compensate for engine problems, making it possible to drive for a very long time–years even–without having any evidence of a severe driveability problem, even though the car is on the verge of failure. Then, suddenly (at least to the car owner), it simply doesn’t run anymore.

10) With modern automotive technology, it’s not about screwdrivers and wrenches, or even about computer tools. Knowing what needs doing is where the expertise comes in. Anybody can hold a paintbrush; but not everybody can paint a great landscape.

———

Emissions Basics

There are essentially five gases that are looked at in emissions testing: carbon monoxide (CO), carbon dioxide (CO2), oxygen (O2), hydrocarbons (HC), and nitrogen oxide (NOx). They are all present in the exhaust stream, but in varying percentages depending on the effectiveness of combustion. Most diagnostics concentrate on HC, CO, and NOx.

High hydrocarbon (HC) emissions usually result from a misfire due to fouled spark plugs, a failing ignition coil, or bad plug wires. However, high HC numbers can also result from poor combustion sealing as a result of worn valves, very rich fuel conditions from oxygen sensor or fuel injector malfunctions, or a host of other problems, including vacuum leaks that “fool” engine computers.

A high carbon monoxide (CO) reading is evidence of a rich fuel-air mixture. This can be the result of leaky injectors, excessive fuel pressure, and sluggish or contaminated O2 sensors.

High nitrogen oxide (NOx) emissions are evidence of lean, hot combustion. Causes include a defective or plugged exhaust gas recirculation (EGR) valve or manifold ports, a failed EGR vacuum solenoid or motor, improper ignition timing, or engine overheating.

Vehicles can also fail an emissions test if the evaporative emissions system is not operating properly. The charcoal canister, purge valve, and related passages can become blocked or broken; the gas cap, part of the sealing of the system, can cause a fault if it is not tightened properly or can no longer maintain system pressure. Often this is the cause of a Check Engine light illumination.