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.
Diagnostic System Operation
The ECM of the DEC system is equipped with a self-diagnostic system which detects system failures or abnormalities. However, the system does not store trouble codes or provide a visual display of malfunctions. To determine the cause of driveability problems, a Diesel Diagnostic Check (DDC) tester (J 34750 or equivalent) must be connected to the system. See Fig 1 .
The DDC tester must be used to accurately diagnosis the cause of any problems which may be related to the DEC system. This is the only special tool required to service the DEC system.
An Assembly Line Data Link (ALDL) connector located under left side of instrument panel (under driver's seat on van models) is used by factory technicians to check the system prior to shipment. This ALDL connector is also used to make specific checks on the system by service personnel. See Fig 2 .
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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.