How do you use a vapor leak detection pump on a Grand Cherokee?


Quick Answer

A Jeep Grand Cherokee's vapor leak detection pump automatically tests for leaks in the vehicle's evaporative emission system, giving a warning when there is a problem to prevent fuel vapors from escaping into the air. Governmental environmental regulations require an LDP to diagnose issues with a car's EVAP system whenever the vehicle is started.

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Full Answer

To test the EVAP system, use a vent valve that seals off the system, then an electric-powered vacuum pump can pressurize the entire EVAP system to 0.25 psi. A diaphragm in the pump draws air in through the filter and pushes it into the system. A magnetic reed switch connects the diaphragm to the Powertrain Control Module, allowing the vehicle's onboard computer to monitor its movement and record variations in air pressure to determine the presence of leaks and to calculate their sizes. When a leak is detected, the PCM activates a dashboard warning light.

Multiple issues can cause an EVAP leak warning, including pressure changes from weather or elevation variations. First, try tightening or replacing the fuel tank cap, then look for loose connections in the hoses and clamps. If the Grand Cherokee's LDP continues to indicate a warning, take the vehicle to a mechanic. In the case of breaks or tears in the hoses or fuel tank itself, it's necessary to replace the damaged equipment.

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