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-420D
Condition
When the control module activates evaporative emission system (EVAP) control, the idle air trim or short-term fuel trim will change. The diagnostic trouble code (DTC) is stored if the engine control module (ECM) does not detect any change in the idle air trim or the long term fuel trim when evaporative emission (EVAP) control is active. The engine control module (ECM) interprets this as a damaged evaporative emission (EVAP) system.
Substitute Value
- None.
Possible Source
- Blocked hose between the EVAP canister and the evaporative emission system (EVAP) valve
- Blocked hose between the evaporative emission system (EVAP) valve and the intake manifold
- Damaged evaporative emission system (EVAP) valve.
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.