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 trouble code (DTC) information ECM-421D
Condition
The diagnostic trouble code (DTC) is stored if the engine control module (ECM) registers that the signal from the evaporative emission system (EVAP) valve is too low.
The diagnostic trouble code (DTC) can be diagnosed when the ignition is switched on.
Substitute Value
- twin heated oxygen sensor (HO2S) control disabled.
Possible Source
- Short-circuit to ground in the signal cable.
Fault symptom[s]
- Malfunction indicator lamp (MIL) lit.
NO RELATED
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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.