Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCHEVROLET1990R 20 P/U 2WD V8-379 6.2L DSLREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTCOMPUTERS AND CONTROL SYSTEMSTESTING AND INSPECTIONSCAN TOOL TESTING AND PROCEDURES
1990 Chevrolet R 20 P/U 2WD V8-379 6.2L DSL
Scan Tool Testing and Procedures
1990 Chevrolet R 20 P/U 2WD V8-379 6.2L DSLSECTION Scan Tool Testing and Procedures
The tool manufacturers have developed "Scan" tools to interface with the diesel electronic control system, through the ALDL. It supplies a visual reading of most inputs to the ECM and some outputs. Review the tool instruction manual to understand its operation and limitations.
When the tool is connected to the ALDL and cigarette/cigar lighter connector or 12 volts, there should be a visual instruction displayed. If there is no display, or tool reads "No DATA" or "No ALDL," refer to "ECM Check" diagnosis and tool instructions to be sure that 6.2L diesel engine is available in the tool.
With the tool in the code position, the display window will indicate any code stored in the ECM memory. Referring to the applicable code chart, the tool will "Scan" an input to determine if a specific circuit is operating properly.
When the tool is connected to the ALDL and cigarette/cigar lighter connector or 12 volts, there should be a visual instruction displayed. If there is no display, or tool reads "No DATA" or "No ALDL," refer to "ECM Check" diagnosis and tool instructions to be sure that 6.2L diesel engine is available in the tool.
With the tool in the code position, the display window will indicate any code stored in the ECM memory. Referring to the applicable code chart, the tool will "Scan" an input to determine if a specific circuit is operating properly.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.