What Does P1478 Mean?
The Leak Detection Pump has detected a clamped, kinked, or blocked tube in the EVAP system. This prevents proper vacuum generation during leak testing as airflow is restricted in the system.
Common Causes
40%
Kinked or collapsed EVAP hose between canister and tank
25%
Clamped or pinched line during previous repair or installation
20%
Failed or stuck closed vent valve blocking airflow
10%
Blocked charcoal canister from fuel contamination
5%
Debris or insect nest blocking vent filter
Diagnostic Steps
1
Step 1: Visually inspect all accessible EVAP hoses and lines for kinks, collapses, or pinch points
2
Step 2: Check canister vent filter and vent valve for blockages or restrictions
3
Step 3: Test vent valve operation using scan tool commands, verify it opens and closes properly
4
Step 4: Disconnect EVAP lines at key points and attempt to blow air through to locate restriction
5
Step 5: Inspect routing of EVAP lines along chassis for any crush points or interference with components
Estimated Repair Cost
$100 - $400
Parts + labor, varies by vehicle and location
The Leak Detection Pump has detected a clamped, kinked, or blocked tube in the EVAP system. This prevents proper vacuum generation during leak testing as airflow is restricted in the system.
The most common cause of P1478 (EVAP Emission Contr.LDP Circ Clamped Tube Detected) is: Kinked or collapsed EVAP hose between canister and tank
Typical repair costs for P1478 range from $100 to $400, depending on the vehicle, location, and whether you do it yourself or go to a shop.
No safety concerns for vehicle operation. Will cause emissions test failure and may produce fuel vapor odors in severe blockage cases.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1478 to identify the root cause.
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Quick Info
Category
Powertrain
System
Emissions Control (EVAP)
Difficulty
Type
Manufacturer
Recommended Tools
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