Scott Shotton
Scott Shotton
Scott Shotton is the owner of The Driveability Guys, driveabilityguys.com, a mobile diagnostics and training company in the northern Illinois area. Scott Shotton has over 20 years of technical experience in automotive repair shops. He currently teaches automotive technology at Kishwaukee College and performs mobile diagnostics and reprogramming for local repair shops
Oxygen Sensors, Part I
Continuing with our recent theme of inputs, this month we’ll cover oxygen sensors. There’s a lot of information you need to know to understand oxygen sensor operation and testing. As a result, we’ll cover basic sensor testing this month and some more advanced theory in the next issue. The Oxygen Sensor’s Job An oxygen sensor’s main purpose is to provide the PCM with a feedback signal i...

Pressure Sensors
Two months ago, we covered testing potentiometers, such as TP and APP sensors. Both of those sensors could cause driveability complaints, transmission shift problems, and cause the MIL to light. This month, we’ll cover pressure sensors. MAP and BARO sensors were more common prior to 1996 with the exception of a few manufacturers. Around the introduction of OBD-II, mass airflow sensors (MAF) b...

Tips on TPS
A faulty throttle position sensor (TPS) or accelerator pedal position sensor (APP) can cause engine or transmission issues. Hesitations, surging, hard starting and a variety of transmission shifting problems are only a few of the issues a failing TPS or APP can cause. Although they aren’t high failure items, we do need to know how to diagnose them properly, especially when they don’t set a ...

Pressure and Vacuum Diagnosis, Part III: Running Compression
In the last two issues of GEARS Magazine, we covered engine mechanical testing using high current probes for relative compression testing in conjunction with transducers for cranking vacuum testing. We also touched on in-cylinder cranking compression testing using a pressure transducer. This month we’ll expand our in-cylinder testing by using a pressure transducer to analyze running compressi...

Pressure and Vacuum Diagnosis, Part II: Cranking Vacuum
Last month’s article covered the tooling and some basic theories regarding mechanical testing using electronic means. This month we’ll dig a bit deeper into cranking vacuum analysis. When diagnosing a misfire, these techniques allow you to evaluate, in great detail, what could be causing low compression, without disassembling the engine. Often you can make these diagnostic decisions very qu...

Pressure and Vacuum Diagnosis, Part I: The Tooling
In the October/November 2017 issue of GEARS, the column In Front of the Flywheel addressed an intermittent compression issue on a 2010 Ford F150. The article referred to vacuum and pressure transducer testing that would be covered in the future. Well, we’re back to visit this very subject. Over the next few issues, we’ll cover the information you’ll need to apply using a transducer for en...

Understanding Digital Signal Sensors
This past October, I presented a class at the ATRA Powertrain Expo in Las Vegas. The event was amazing! I’d personally like to thank everyone who was involved in putting this event together. It was a necessary component for technicians to train and stay at the top of their games. The class I presented covered digital storage oscilloscope use, specifically the testing of permanent magnet gener...

Intermittent Compression
Can a vehicle have a misfire caused by intermittent compression? If so, can a compression gauge catch it? The answers are “Yes,” and “Only if you’re lucky,” respectively. In this issue, we’ll tackle a vehicle with this very condition. We’re going to need some history for this one. The vehicle is a 2010 Ford F150 equipped with a 4.6 liter, 3-valve engine. The customer’s complaint...

How Much Alcohol Is Too Much?
Many technicians today still don’t have to deal with ethanol. Others do, but they aren’t usually the ones who get caught with their pants down when it comes to these problems. Some basic knowledge and testing procedures will greatly save diagnostic time when that one-in-a-thousand ethanol issue rolls in your door and sends you spiraling down the rabbit hole. One thing you can be sure of:...

Piercing and Probing… the Tension
Backprobe or pierce? That’s a philosophical question that has plagued technicians for years. Turns out there may be a real benefit to piercing wires instead of backprobing the terminals: It could help you identify loose terminal connections.

Scan Tool 1–2–3
Almost every system on today’s vehicles requires the use of a scan tool for diagnostics or reprogramming. Which leads to a common question: “What scan tool should I buy?” The best answer usually isn’t what you might hope: All of them. Since purchasing every OEM scan tool would be cost prohibitive for most, and return on investment would be poor for some tools in some markets, let’s ex...

Computer Communication Troubles, Part I
Many of you have probably run into speed sensor issues on a Chrysler product that set gear ratio error codes, input shaft speed sensor codes, or output shaft speed sensor codes. These codes confuse the transmission control module (TCM), putting the system into failsafe. But there are many issues that can cause this. Lately, network communication issues have become a common problem. Today’s ve...

Put Your Fuel Pressure Gauge Back in Your Box
Here’s something for you to think about: Your fuel pressure gauge is basically worthless, because fuel pressure doesn’t matter. Actually, let’s modify that slightly: Fuel pressure is necessary, but measuring fuel pressure is a worthless test in most cases. Here’s why: Correct fuel pressure is required for injection pressures to be correct. But fuel volume is required to maintain the app...

Misfire? Here's Some Direction
This month, we’ll look at how to use scan data to help identify a misfire. For an engine to run correctly, it needs three main things: compression, spark, and the correct air/fuel mixture. If any of these is missing, the result will be no combustion in the affected cylinder There are a number of tests to help determine which of these items is at fault. You can test fuel injectors, scope the s...

Engine Mechanical: Go/No-Go
Have you ever had a misfire where you wanted to do a compression test on a cylinder that was buried underneath an intake manifold? Or worse, gone through all that effort to perform a compression test, only to discover that the compression was fine? There’s an easier way. In this issue, we’ll cover the use of a relative compression test to make a quick Go/No-Go decision on the mechanical con...

Nail Down Those Troublesome Ford Ignition Coils
Last month we covered a relatively universal method of narrowing potential causes for misfire using scan data. The timing of the article’s publication was ideal. I was privileged enough to present this very topic at ATRA’s Powertrain Expo a few weeks ago. I had a wonderful time presenting and, more importantly, discussing the topic with technicians after the presentation. During these co...

Computer Communications Troubles, Part II
In the last issue of GEARS, we examined how to diagnose a single module that wouldn’t communicate. We covered the three requirements for a module to operate: power, ground, and its ability to communicate. This month, we’ll examine a vehicle that has problems with multiple modules. The diagnostic approach will be slightly different, because the vehicle’s fault is different. As always, a ne...

Put Fuel Trim to Work for You
In this article, we’ll continue to build on the fuel trim basics we covered in the May 2016 issue. We’ll also be referring to the information we discussed late last year on engine breathing or volumetric efficiency. Our goal this month is to use knowledge and scan data to quickly narrow down the potential causes of fuel trim related codes. You can often perform this process-of-elimination s...

Fuel Trim: Your Crystal Ball
In the last issue of GEARS we looked at oxygen sensor testing, and it brought up some interesting questions about fuel trim. As a result, we’ll spend the next few articles learning to understand fuel trim numbers and their diagnostic value. In a way, fuel trim is line a “crystal ball” that allows you to see what the PCM is trying to do. This month we’ll cover the basics of fuel trim, to...

Don't Break Out the Shotgun for Those O2 Codes
Since the introduction of On-Board Diagnostics, Generation 2, or OBD-II, PCMs have done a pretty good job of monitoring oxygen sensors and setting diagnostic trouble codes when they're faulty. Some of the things the PCM monitors for this are signal amplitude, sensor response time, rich limit, and lean limit. But sometimes these monitors don't pick out the fault with the vehicle accurately. If y...