Redtruck-VA
Senior Member
- Joined
- Jun 29, 2010
- Posts
- 5,864
- Reaction score
- 984
- Location
- Virginia
- Ram Year
- 2003 & 1989 D250 RWD
- Engine
- Hemi-5.7, 5.9 12v & 24v diesel
Became curious when an overseas member asked about removing the entire EVAP system from his 03. Since most if not all Hemi models are NGC they have the Natural Vacuum Leak Detection (NVLD) system. This is actually a very simple system with only three wires attached to it.
1. A ground wire.
2. A switch sense wire (normally open).
3. A solenoid valve (normally closed unpowered).
The evap test actually occurs when the engine is turned off and is centered around a change of pressure (vacuum) within the sealed tank due to any temperature change. If the tank is NOT sealed then there is no vacuum to close the switch.
Upon engine startup the switch sense (open or closed) is sent to the PCM to indicate if the tank is sealed or not. If the switch sense is “closed” this indicates the tank has held a vacuum and the system is functioning. The solenoid then opens the valve allowing the tank to breath for remainder of run time. If the switch sense is open then this indicates the tank is not sealed and the PCM moves to the next test which has the solenoid close the valve (no power) and looks for the switch to close indicating vacuum. If this test fails (switch sense open) then a DTC is set.
I see is a direct relationship between switch sense and solenoid being “powered”. So using a standard 12vdc relay with the normally closed (NC) contacts wired to the switch sense indicating “switch closed” every time the engine was started the PCM would see the tank is sealed. And the solenoid would then be powered to open the valve for normal operation and the switch sense would then open. My conclusion is a simple relay can replace the NVLP/ evap system with no codes.
Inputs are always appreciated.
1. A ground wire.
2. A switch sense wire (normally open).
3. A solenoid valve (normally closed unpowered).
The evap test actually occurs when the engine is turned off and is centered around a change of pressure (vacuum) within the sealed tank due to any temperature change. If the tank is NOT sealed then there is no vacuum to close the switch.
Upon engine startup the switch sense (open or closed) is sent to the PCM to indicate if the tank is sealed or not. If the switch sense is “closed” this indicates the tank has held a vacuum and the system is functioning. The solenoid then opens the valve allowing the tank to breath for remainder of run time. If the switch sense is open then this indicates the tank is not sealed and the PCM moves to the next test which has the solenoid close the valve (no power) and looks for the switch to close indicating vacuum. If this test fails (switch sense open) then a DTC is set.
I see is a direct relationship between switch sense and solenoid being “powered”. So using a standard 12vdc relay with the normally closed (NC) contacts wired to the switch sense indicating “switch closed” every time the engine was started the PCM would see the tank is sealed. And the solenoid would then be powered to open the valve for normal operation and the switch sense would then open. My conclusion is a simple relay can replace the NVLP/ evap system with no codes.
Inputs are always appreciated.