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.
DTC 300: Diagnostic Link Defective: Explanation
Diagnostic link TxD or RxD has an open or has a short to voltage or ground. The TxD link leads from the diagnostic socket pin No. 20 to the EGS control unit pin No. 13 and is bypassed to ground when the cover of the diagnostic socket is closed. The RxD links leads from the diagnostic socket pin No. 15 to EGS control unit pin No. 25 and is bypassed to terminal No. 30 when the cover of the diagnostic socket is closed.
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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.
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