Testing Chrysler Evap Systems

Testing Chrysler Evap Systems. PAGEREF _Toc155001438 \h 1 08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000E0000005F0054006F0063003100350035003000300031003400330038000000

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Checking the Sensing Switch.. PAGEREF _Toc155001440 \h 7 08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000E0000005F0054006F0063003100350035003000300031003400340030000000

Like any other manufacturer, Chrysler products have their share of evap leaks causing trouble codes P0455, P0442, and P0456. Loose or bad gas caps are often the source of the trouble, but what if there is an actual leak? How can the evap system be sealed so that a smoke tester can be used to locate the leak? While the leak detection pump can be confusing, sealing the system is easy, even if you do not own a scan tool with the capability to seal the system.

The first step is to locate the purge valve and unplug the electrical connector. Next, locate the large vacuum hose from the purge valve to the intake manifold. Disconnect it from the manifold and plug the vacuum leak. The purge valve will be located under the hood somewhere, but the exact location can vary depending on the year and model.

Next, locate the leak detection pump (LDP). On most Jeep vehicles the LDP is located behind the left headlamp. On the Caravan, the LDP is located under the vehicle on the engine cradle. On other Chrysler products you may locate the LDP under the hood or in the rear near the fuel tank. The picture below is a leak detection pump from a Dodge Grand Caravan.

The next image is a LDP from a Jeep Grand Cherokee. The circuits have been labeled on this picture.

Use a wiring diagram to locate the solenoid control circuit on the LDP connector. The wire color will vary depending on the exact vehicle, but it is usually the center of the 3 wires at the connector. NOTE: Do not backprobe the wrong connector. Doing so can short out the power supply and damage other components. With the connector unplugged and the engine running, the solenoid control circuit will NOT have B+ voltage. Double check before back-probing this circuit.

Once the solenoid control circuit has been identified, backprobe the connector while leaving it connected to the LDP. Now connect a jumper wire to a good ground source (see the example below)

Now, remove the green service port cap on the evap line that should be located near the purge valve. Connect a smoke machine to the evap line. Using a smoke machine with a flow meter is the best testing method. The flow meter can tell you IF a leak exists without having to search the vehicle from one end to the other with a flashlight while looking for wisps of smoke. Then, if the flow meter determines that a leak is indeed present, turn on the smoke and locate the leak. If the flow meter shows that the system is sealed, then the evaporative trouble codes are likely caused by either an intermittent sticking purge valve or the gas cap was left loose at one time but may have been tightened before the vehicle was brought into the shop.

Crank the Engine!!

Once all test equipment is in place, start the engine. With the engine running, the purge valve unplugged and the leak detection pump solenoid jumped to ground, the system should be sealed. Before turning on the smoke and wasting time looking for a leak that may not even be there, use the flow meter to determine if a leak is present. Keep pumping nitrogen into the evap system for a couple of minutes. The flow meter should show significant flow at first, but then begin to slow as the tank fills with nitrogen or other inert gas (DO NOT USE SHOP AIR, AN EXPLOSION COULD OCCUR). If the tank is low on fuel, it could take up to 2 or 3 minutes before the flow meter will begin to drop. Also, make sure your smoke machine will only produce 1 PSI of pressure. More than 1 PSI could damage evap components or cause a fire/explosion.