DLC Scan Tools

The PCM can communicate a variety of information through the DLC. This data is transmitted at a high-frequency which requires a Scan tool for interpretation. There are several Scan tools available for reading this information.


With an understanding of the data which the tool displays, and knowledge of the circuits involved, the tool can be very useful in obtaining information which would be more difficult or impossible to obtain with other equipment.


Scan tools do not make the use of diagnostic charts unnecessary, nor can they indicate exactly where a problem is in a particular circuit. Trouble code diagnostic charts incorporate diagnosis procedures using a Scan tool where possible and most charts require the use of a Scan tool when it is applicable.


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 manufacturer's operating manual to become familiar with the tool's operation.


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) or the SERVICE lamp turns On momentarily or when engine drive ability is momentarily poor. An assistant should be used when driving a vehicle and using a Scan tool. 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 when a diagnostic trouble code is stored. This information can be found with a Saturn Scan tool (portable diagnostic tool [PDT]), listed under MALF history. This information can be very useful when attempting to troubleshoot intermittent diagnostic trouble codes.