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How to shop for a scan tool

How to shop for a scan tool or code reader

Step #1: When shopping for a scan tool or code reader understand that diagnosing a problem requires more than just the trouble code

A trouble code is not a diagnosis. It’s a starting point. A scan tool and code reader will both give you the trouble code. But a trouble code just tells you that the data the car’s computer is seeing is out of spec. If you replace whatever part is mentioned in the trouble code, you’ll be making the single most common and costly mistake made by the majority of DIYers.

A trouble code is not a diagnosis

Let’s look at the most commonly misdiagnosed trouble code: P0131 O2 Sensor Circuit Low Voltage (Bank 1 Sensor 1). This code is telling you that the Bank 1 Sensor 1 oxygen sensor is reporting a consistently low voltage. Most DIYers replace the oxygen sensor. Then the code returns. Why? Because the sensor was fine and was actually reporting exactly what it was seeing in the exhaust stream. The DIYer just decided to kill the messenger and condemn the sensor. The big question and the proper way to approach diagnostics is to ask, “WHY is the oxygen sensor reporting consistently low voltage?” In most cases, the root cause is a vacuum leak, clogged fuel injector or weak fuel pump that’s causing a lean air/fuel mixture.

A real-world example of diagnosing versus parts replacement

Let’s use a medical analogy: You go to the doctor and the nurse takes your blood pressure. It’s 85/40; a reading that’s too low for a healthy person. A typical DIYer would see that reading, and without doing any further testing, they replace the heart. But a real Doctor would conduct more tests to find out why the  blood pressure is so low.

A scan tool can help with testing. A code reader can’t

All late model vehicles allow you to peer into the computer and view the actual data from the sensor. A scan tool with a live data feature allows you to see the data. If you have just a code reader, you’ll have to use a digital multimeter to test individual sensors, and even then you won’t have all the data you need to properly diagnose the root cause of the trouble code.

Step #2 when shopping for a scan tool or code reader understand the difference between P, C, B and U trouble codes and generic versus manufacturer specific codes

All trouble codes are at least five digits, starting with a letter. The letter tells you which system is reporting the code.

P codes refer to the vehicle’s powertrain: engine, transmission, emissions system, cooling system, and electrical system

B codes refer to body systems like airbags, seat belts, fuel tanks, mirrors

C codes refer to chassis systems like brakes, anti-lock brakes, stability control, traction control

U codes refer to communication and network systems.

In each code category, there are generic codes that mean the same thing across all carmakers and manufacturer-specific codes that can vary from one carmaker to another and even from one year and model to another. The second digit denotes generic versus manufacturer-specific

P: Powertrain codes
P0xxx – Generic
P1xxx – Manufacturer-specific
P2xxx – Generic
P30xx-P33xx – Manufacturer-specific
P34xx-P39xx – Generic

C: Chassis codes
C0xxx – Generic
C1xxx – Manufacturer-specific
C2xxx – Manufacturer-specific
C3xxx – Generic

B: Body codes
B0xxx – Generic
B1xxx – Manufacturer-specific
B2xxx – Manufacturer-specific
B3xxx – Generic

U: Communication codes
U0xxx – Generic
U1xxx – Manufacturer-specific
U2xxx – Manufacturer-specific
U3xxx – Generic

The least expensive code readers only display generic P codes. They can’t see or display C, B or U codes.

Step #3 when shopping for a scan tool or code reader understand how much live data the tool provides and whether the tool is bi-directional

Most code readers don’t display live data and usually only display generic powertrain codes. Inexpensive scan tools show you a very limited palette of live data and usually only on the powertrain system. A higher-end scan tool allows you to see live data for body, chassis and communications systems in the vehicle but may limit you to only generic codes, while other show you generic and manufacturer-specific codes. Some scan tools and code readers show

The more live data the tool displays, the more information you’ll have to diagnose the problem

What a bi-directional scan tool does for you

A bi-directional scan tool allows you to command solenoids, fans, and valves on and off, while also reading live data. Here’s an example. The car is overheating and you want to make sure the electric radiator fans are working. A bi-directional scan tool allows you to turn on the fans. Without that feature, you’d have to hot wire the fan.

Step #4 when shopping for a scan tool or code reader understand what freeze-frame snapshot capabilities get you.

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.

Step #5 when shopping for a scan tool or code reader understand what Mode $06 is and how it can help you.

Auto computers set trouble codes when sensors

Mode $06

Mode $06 data

detect values that exceed the manufacturer’s specifications by a certain amount or the 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, just 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 all the spark plugs are reaching the end of their life?

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.

Step #6 when shopping for a scan tool or code reader, buy one that gives you the code definition.

What good is getting a P0344 if you don’t know what it means? 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.

bugs in their software and all you need is a software update.

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)   A 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.

Buying a counterfeit 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.

©, 2017 Rick Muscoplat

Posted on by Rick Muscoplat

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