P0442 - Evaporative Emission System (EVAP) Leak Detected (small leak)
System
Powertrain (Engine & Gearbox)
Technical Description
The control module has detected a fault in the Evaporative Emission System (EVAP) Leak Detected (small leak) (P0442). The module sees no circuit at all — broken wire, backed-out pin, or a failed sensor.
Multimeter Test Points & Nominal Values
| Test Point / Component | Measurement | Nominal Target Range | Test Condition |
|---|---|---|---|
| Evaporative Emission System (EVAP) Leak Detected (small leak) – Coil Resistance | Resistance (Ω) | 3 - 30 Ω (typical) | Connector disconnected at 20°C |
| Evaporative Emission System (EVAP) Leak Detected (small leak) – Duty Cycle | PWM (%) | 5 - 95 % (modulates with target) | Engine running, actuator in control |
| Evaporative Emission System (EVAP) Leak Detected (small leak) – Supply Voltage | Voltage (V) | 11.8 - 14.4 V | Ignition ON at connector |
Connector disconnected at 20°C
Engine running, actuator in control
Ignition ON at connector
Oscilloscope Waveform Analysis
2 ms/div, 20 V/divPossible Causes
Open circuit, damaged wiring harness, or disconnected plug at Evaporative Emission System (EVAP) Leak Detected (small leak)
Chafed or pinched wiring harness along the signal path to Evaporative Emission System (EVAP) Leak Detected (small leak)
Internal mechanical wear or carbon deposits inside Evaporative Emission System (EVAP) Leak Detected (small leak)
Defective internal output driver or reference circuit in the control module for Evaporative Emission System (EVAP) Leak Detected (small leak)
Symptoms
Recommended Solution
Verify continuity (< 0.5 Ω) on the signal wire between the component plug and the ECM header connector.
Verify loaded supply voltage and harness terminal pins at Evaporative Emission System (EVAP) Leak Detected (small leak).
Check circuit continuity and ground-side voltage drop (< 0.05 V) for Evaporative Emission System (EVAP) Leak Detected (small leak).
Check supply and the low-side driver at the ECM connector. Replace the actuator or repair the circuit based on the readings.
Mechanic's Tip
Use the scan-tool output test with the scope on the control side at the same time. If duty changes but the actuator does not move, the valve is stuck — not the electrical fault you were chasing.