Rick's Free Auto Repair Advice

How to buy a scan tool

Buy a scan tool or a code reader?

Let’s get this out of the way right up front. You have to make

buy a scan tool

Bosch Code Reader

a decision right away whether you’re going to buy a scan tool or a code reader. A cheap code reader is better than nothing, but not by much. Most cheap code readers will only read generic powertrain (P) codes P0001- P0799. Car makers limited themselves to those codes in the early days of On Board Diagnostic II. But not anymore. OBDII allows car makers to make up their own codes and code definitions to cover unique conditions and model specific applications. These powertrain (P) codes start at P1000 and go up to P3000. These “enhanced” or OEM trouble codes can be vehicle specific and can be different from one model year to the next. That makes code reading far more difficult because those codes and code definitions take up a lot of memory space and they must be updated somehow.

In addition to differences between generic and enhanced or OEM P trouble codes, car makers also use Chassis (C), Body (B), and Data communications (U) trouble codes. Few if any code readers read those codes. Here are some examples of enhanced OEM codes and C, B and U codes

Actron scan tool

Actron CP9690

P2100 Throttle Actuator Control (TAC) Motor Control Circuit

B210C Battery voltage input-Circuit voltage below threshold

C123F Steering angle sensor comparative performance

U0026 CAN B Bus (-) Circuit High

So the truth is, you really can’t get by with a code reader anymore. Here’s what’ll happen if you cheap out and buy a scan tool. You’ll get a written message like: “Reduced Power” on a driver’s information display or simply a Service Engine Soon light and you’ll plug in your code reader. What’ll you get? NO CODES stored. Why? Because there are NO generic P codes stored. You probably have an enhanced, B, C or U code stored. I see this every day in automotive forums where readers write in and say they took their vehicle to an auto parts store and the clerk said there were no trouble codes. That’s because they’re using CODE READERS, not scan tools. Now that you know the difference, let’s talk about scan tools

What to look for in a scan tool

Your scan tool must have live data capabilities

If you’re going to do your own diagnostic work, you

freeze frame data

Snapshot freeze frame

MUST buy a scan tool that provides LIVE DATA. The ability to see voltage and sensor values right on the scan tool screen saves you the trouble of tapping into individual sensors and trying to get a live reading there. At the very least you want to see:

Long and short term fuel trims—those readings tell you if the computer is adding or subtracting fuel to keep the engine running. If you have a vacuum leak, a car computer will typically see a lean reading at the oxygen sensors and compensate by adding fuel. Short term fuel trim usually maxes out at 25% added fuel. At that point, if the computer still sees a lean condition, it will move into long term fuel trims based on the assumption that the problem isn’t temporary.

Oxygen sensor values

Engine coolant temperature sensor

MAF sensor

MAP sensor

Intake air temperature

Transmission input sensor

Transmission output sensor


Knock sensor

Open/closed loop status

Buy a scan tool with snapshot freeze frame features

Sometimes you’re dealing with an intermittent problem and that’s when the snapshot feature comes in handle. You drive the vehicle with the scan tool attached and press the snapshot freeze frame button on the scan tool when the problem occurs. The scan tool stores the 30 frames of data before you pushed the button and 30 frames of data after you pushed the button. This is an invaluable feature that can save you a lot of aggravation.

Buy a scan tool with Mode $06 capabilities

Auto computers set trouble codes when sensors

Mode $06

Mode $06 data

detect values that exceed manufacturer’s specifications by a certain amount or failure happens more than X number of times. So you may see a P0304 trouble code telling you that cylinder 4 has had enough misfires to qualify as a problem. If that’s all you know, you may think that the problem is limited to only cylinder 4. But what if other cylinders are misfiring but not often enough to set a trouble code. Wouldn’t you like to know how the other cylinders are doing before you dive in to fix just cylinder 4? What if you need all new spark plugs or spark plug wires?

Well, Mode $06 lets you peek behind the curtain and see EXACTLY what information is stored in your car’s computer. If cylinder #1 has had 99 misfires but the threshold for setting a trouble code is 100, Mode $06 can show you that data and you’ll know you’ve got an issue there as well.

Buy a scan tool with code definitions built in

What good is getting a P0344 if you don’t know what it means? As I said earlier, storing trouble code definitions takes up memory in the scan tool, and car makers are constantly adding new codes. The better scan tools allow you to update the trouble code look up tables by plugging the unit into your home computer and downloading the latest definitions.

Buy a scan tool with a pattern failure database

Several scan tool companies partner with tech support services that’ll tell you the most common cause of each trouble code based on the year, make and model. In addition, those same services let you know if the car maker has issued a technical service bulletin with new repair instructions or updated parts.

Reading the most recent technical service bulletins can save you a LOT of time. In fact, on late model vehicles, MOST trouble codes can be fixed without replacing any parts because car makers have fixed the bugs in their software and all you need is a software update.

Buy a scan tool that’s CAN compliant with bi-directional features

In the old days, scan tools were passive; they only received information. As car makers added data lines from one module to another, techs needed the ability to send commands to the modules. Car makers responded by installing a Controller Area Network, or CAN bus. A CAN system relays information much faster to the scan tool and can accept commands from the tools.

A bi-directional scan tool can communicate with the vehicle computers and actually send commands. Having a problem with an EVAPORATIVE emission purge valve (very common) and want to check it out? With a bi-directional scan tool you can apply a vacuum to the valve with a handheld vacuum pump and then command the valve to open or close from your bi-directional scan tool. If the valve fails to hold vacuum or doesn’t open or close, you have nailed the problem.

Stand-alone scan tool or Bluetooth?

Lots of companies sell Bluetooth scan tools that plug into the diagnostic port on your car. The “dongle” communicates with your phone, PC or tablet via Bluetooth. They work fairly well and they are reasonably priced. But there are several drawbacks:

1)       The dongle relies on the computing power and memory storage in your phone. If you have an older phone or one with limited memory storage, the screen won’t update as often and you’ll lose important live data.

2)       Some of the units store almost nothing on your phone and rely on your WiFi or mobile data connection to ping the company’s database to download trouble code definitions, technical service bulletins and pattern failure reports. That’s not a problem if you get strong WiFi in your garage, as long as you know ahead of time that you must be tethered to either WiFi or mobile data to get that information.

3)       Your phone screen is small and may be hard to read. That may not be a problem when reading a single trouble code, but it can be a huge problem if you’re trying to read a full technical service bulletin on a small screen. In that case you may want to use a Bluetooth dongle with a laptop. A laptop allows you to store more definition data and view it on a larger screen.

Avoid these scan tool buying traps:

Not checking to see if the scan tool works with YOUR vehicle. Some scan tools only work with domestic US cars and a few Japanese cars. European cars often require a different scan tool.

Not checking to see if the scan tool reads B, C, U and enhanced trouble codes

Buying a knock-off. Many Chinese companies are building “knock-off” versions of high end professional scan tools and selling them at a highly discounted rate. You may be tempted to buy one. Don’t, because the software that comes with the tool is the only software you’ll ever be able to use. These knock-off tools WON’T UPDATE. That’s right. Within 6 months, the software will be obsolete and you’ll be stuck with an expensive brick.

What scan tool brand should you buy?

Most companies make several models, so there’s no one brand that rates the best for do it yourselfers. But here’s a list of name brand scan tool manufacturers

• ACTRON • Equus/Innova • GoPoint Technologies (scan tool app for iPhones–Apple approved) • Lemur Monitors (Blue Driver OBD Scantool App) • PLX Devices (scan tool software for iPhones) • TORQUE smart phone scanner app • Autel Auterra AutoBoss • Autologic • Autodiagnos (European scan tools) • Baum Tools(European scan tools) • EASE Diagnostics • Launch

Actron scan tools

Innova scan tools

Blue Driver scan tools

©, 2017 Rick Muscoplat

Posted on by Rick Muscoplat

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