Digital Bits Technology Column

HomeDigital Bits Science Lab - Science experiments for parents and childrenDigital Bits column archivesView reviews and reportsReader Questions and Answers

Custom Search

Send Andy an email Fequently Asked QuestionsWho's responsible here?

Email updates

This is the Digital Bits Tech Column's RSS feed. You will need an RSS news aggregator to use it. (Click the 'What is RSS?' link for more detail. ?

This site is part of the
Digital Bits Network, LLC.

OBD-II code readers: Listen when your car speaks

You're standing next to someone and they suddenly yelp "technology!" What would you think? First, you should back away slowly. After you're safe, avoiding eye contact, you'd think, "Technology. Beeping, blipping computers. Things we type on and talk into and sometimes want to smack with a large hammer."

Well, not today. Today we're getting dirty, greasy and oily. And maybe just a little smelly. Technology comes in many forms, and some are automotive. Let's take a drive.

Today's do-it-yourself weekend mechanics are frustrated. Gone are the days when they could get under the hood, remove parts, and put things together again without worrying about the car's computer. Fuel systems, ignition timing, temperature sensors and more: Most are controlled and monitored by computer. You've got to have at least a vague idea of what you're doing. Short circuit the wrong terminals, and FWOOSH – insty-airbag deployment, or KAZAKKLE – you've just fried your car's internal computer chips.

When something goes wrong with these systems, a light appears on our dashboard display, telling us "Service Engine Soon" or "Check Engine". When you see this light happily shining for the first time, does your car need some basic maintenance, or is your engine about to explode?

So you visit a mechanic. He tells you it's nothing to worry about. You just need some new blinker fluid. No problem, $10 for the fluid, and $50 for the diagnostic. How did he know? He may have used a special computer interface, allowing his computer to talk with your car's computer. The car tells him what's wrong by showing a diagnostic code.

Called OBD-II (oh-bee-dee-two), a special plug is available on all cars 1996 and newer. This computer interface standardizes the way we monitor emissions and other critical systems.

Think of how handy this is by comparison to the human-world: Go to the doctor, have a cable shoved up your nose, and listen as a computer announces, "Patient has Amaxophobia: Prescribe over-advertised medication and call me in the morning."

Read your car's Check Engine light yourself in about ten seconds: The Actron CP9135 ODBII AutoScanner, $100 on eBay and Amazon, is a small OBD-II handheld code reader. Plug it in to your car, and display problem codes or erase them if you think you've fixed the problem:

For monitoring details, use ProScan, available for $100-$160 at http://myscantool.com. View tech-level info like manifold pressure, coolant temperature, and fuel trim settings. Get graphs and readouts of this information in real time. You'll need a Windows laptop, as the software runs on a computer plugged in to your car.

For those wanting more information, but want things simplified, check out CarMD. Give them $90 and you'll get a code reader and some software. Read codes from your car. Then plug the reader in to your PC, and "retrieve diagnostic information, including probable cause, fix and estimated repair costs". Also upload the ODB reader information to the CarMD folks, and you'll get extended diagnostic reports at no additional charge (register up to three cars and get up to three reports per month).

For fans of the open source movement, or people with an interest in ODBII hardware and software design, check out open source ODBII hardware and software from Stern Technologies. They offer multiple ODB scanners and code readers, and also provide source code and ODBII hardware scematics.

If you want the best possible ODBII monitoring tool for laptops and Palm handhelds, and don't mind spending hundreds of dollars, get AutoTap at http://autotap.com. Below are some screen shots of the realtime information auto sensor monitors available from Proscan:

The text above is a little small, so what we're seeing are graphs of Engine Coolant Temperature, Engine RPM, Absolute Throttle Position, and Intake Manifold Absolute Pressure.

How do I find my car's OBDII connector? What does an OBDII plug look like?

Here's where it is in my car, a Saturn SL1. Generally, they're located near the driver's foot area. Legally, they need to be within three feet of the driver, and must not require tools to access. Stick your head near the pedals, open fuse box covers and armrests, and look around.

Advanced ODBII interfaces like ProScan and AutoTap allow us to get low-level analysis of our car's performance, great for advanced weekend mechanics. But even if you can barely change your own oil, handheld readers like the Actron will quickly save you money in diagnostic costs and simple repair jobs.

When your car talks, now you can listen.

Get a listing of generic and manufacturer-specific ODBII trouble codes, or get more information on ODBII interfaces, including free ODBII reader software and hardware kits: http://obddiagnostics.com and http://www.scantool.net.