Scan Tool Diagnostics

05/21/12

Well, it's that time of year again. Time to run the family's 1997 people hauler to the inspection station and run it through. You're not really looking forward to it because the Check Engine Light (MIL) came on yesterday. But you go on out and pull into line and wait your turn.

Well, it failed inspection.

Your vehicle has the second-generation OBD II diagnostic system. OBD II replaced the first-generation OBD I in 1994. OBD II is used by all automakers and is Federally mandated. The problem that DIY's run into is that you can no longer get diagnostic trouble codes (DTC's) by watching the blinking MIL as you could with older computer controlled engines. Taking the vehicle into a shop that has the proper tools to diagnose the problem can be expensive, often $100.00 or more.

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The other option is to learn OBD II and do it your self. The thing is, you're going to need a scan tool.

It's not surprising that the vehicle failed an emissions test with the MIL on. OBD II will only turn the MIL on only if it detects an emission related fault. This is where a scan tool is really nice to have because it will show a lot of problems that won't turn the MIL on.

As with most problems the MIL will remain on even after a repair is made. The DTC remains stored in the computer and will erase after a certain number of key starts, sometimes as many as 50 key starts. However, you can use the scan tool to erase the code immediately.

The OBD II will help you find the answers to simple problems and will also give you the data you need to find the more complex problems. This will give you a better understanding of what is going on with your engine.

An OBD II scan tool will also provide you with engine operating information such as RPM, ignition timing, injector pulse width and readings from a number of sensors such as the O2 sensor, throttle position sensor (TPS) and mass airflow sensor (MAF). It will also show certain switch positions signals.

OBD II also has a "capture" mode where you can get a "picture" of what was happening when an intermittent driveability problem occurred.

Since you can't have Mr. Spock do a full sensor scan on your engine, doing a DTC scan on a regular basis will reveal a problem that has not turned on the MIL.

A scan tool with enhanced diagnostics can save your a lot of time and worry and allow you to do most of the troubleshooting from the drivers seat.

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