Diagnostics Mean More Than Just Scan Tools

At the component level, scan tools have help pinpointing problems.


There is no doubt about it. Scan tools have come a long way. And while their value remains undisputed, there are times when a scan tool may not provide enough information, or give you enough control. At times like these, often at the component level, it's good to know that there are additional tools specially designed to help pinpoint where problems may lie.

Here, we look at some common alternatives to scan tools.

Digital Multimeter
Without question, a digital multimeter is one of the best diagnostic investments. Capable of measuring voltage, resistance, current, frequency, duty cycle and more, a DMM has universal applications for virtually every make, model and onboard system. Most also have add-ons that expand their capabilities even further, including high-current and secondary voltage probes.

A DMM really shines when performing component and circuit tests. You can use it to measure the actual values in that circuit and then determine whether they're in the realm of specifications for that system or component. For instance, a DMM's pulse-width measurement capability allows you to monitor the "on" time of fuel injectors.

Sensor Simulator/Tester
A sensor simulator/tester gives you the capability to simulate a sensor's operation, which can help indicate whether the sensor itself, or its circuit, is at fault. You can also substitute values to see whether the PCM responds, and make changes based on those values. This type of tester usually displays voltage and frequency values, and can be a real asset when trying to track down a pesky mass airflow sensor, manifold absolute pressure sensor, etc.

Fuel Pressure Tester
Fuel pressure is a vital sign of engine performance that simply cannot be underestimated. However, despite its importance, fuel pressure measurements are often overlooked.

Fuel pressure readings can help you determine if there's a bad fuel pump or faulty fuel pressure regulator, as well as to isolate a bad injector. Depending on the system and the test procedures for it, fuel pressure readings can also provide important information about other fuel injection components.

Fuel pressure gauge kits come with various adapters and fittings designed to fit the fuel injection systems of domestic and import cars. Although"American" cars typically have test ports so you can quickly connect a gauge, this is not always the case. For this reason, it's important to consider the makes and models of cars you will be working on when shopping for a fuel pressure test kit.

Lab Scope
A lab scope really shines when checking for the presence and condition of analog and digital signals. For example, analog signals are characteristic of variable reluctance magnetic sensors, such as the crankshaft sensor on some distributorless ignition systems, wheel speed sensors on anti-lock brake systems, and the pickup coil on some electronic ignition systems. The output of this signal is a variable, AC voltage that continuously changes in polarity. The strength of an analog signal depends on the rotating speed of the sensor's trigger wheel. The faster the speed, the stronger the signal. With a lab scope, you can check the voltage and amplitude of the signal to make sure it's electrically sound.

The same holds true of digital signals, which are typical of the Hall-effect sensors used in cam and crank sensors for some engines with distributorless ignitions, and ignition pickups in some electronic ignition systems. By viewing the signal's signature, you can spot glitches in its output.

One favored use of dual-channel lab scopes involves signal comparisons from two input sources. Using this technique, you can compare the synchronization of signals to make sure they're in step with one another.

Exhaust Gas Analyzer
Testing a car's emission levels with a gas analyzer parallels a doctor's analysis in many ways. You take some readings, interpret their levels and relationship to one another, then determine the cause.

This content continues onto the next page...

We Recommend