Scan Tool Usage With Intermittents

In some Scan tool applications, the data update rate makes the tool less effective than a voltmeter, such as when trying to detect an intermittent problem which lasts for a very short time. However, the Scan tool does allow one to manipulate wiring harnesses or components under the hood with the engine not running, while observing the readout of the Scan tool.

The Scan tool can be plugged in and observed while driving the vehicle under the condition when the malfunction indicator lamp (MIL) turns On momentarily or when engine driveability is momentarily poor. If the problem seems to be related to certain parameters that can be checked on the Scan tool, they should be checked while driving the vehicle. If there does not seem to be any correlation between the problem and any specific circuit, the Scan tool can be checked on each position, watching for a period of time to see if there is any change in the readings that would indicate intermittent operation.

The Scan tool is also an easy way to compare the operating parameters of a poorly operating engine with those of a known good one. For example, a sensor may shift in value but not set a diagnostic trouble code. Comparing a sensor's readings with those of a known good vehicle may uncover the problem.

The PCM has the ability to take a snapshot of four pieces of engine data with each diagnostic trouble code stored. This information can be found with a Saturn Scan tool (portable diagnostic tool [PDT]), listed under Malfunction history. This information can be very useful when attempting to troubleshoot intermittent diagnostic trouble codes or flags.

The Scan tool has the ability to save time in diagnosis and prevent the replacement of good parts. The key to using the Scan tool successfully for diagnosis lies in the technician's ability to understand the system being diagnosed, as well as an understanding of the Scan tools operation and limitations. The technician should read the tool manufacture's operating manual to become familiar with the tool's operation.