2002 Grand Caravan ES, and 3.8. Drives with no DTC codes during event that is repeatable. When the van is driven 15 miles or more with a bit over 1/2 tank or less of fuel, the fuel gauge and DTE monitor begins to drop rapidly. In about 30 miles, the fuel gauge will show near empty and DTE will also show the equivalent as if nearly out of fuel. Vehicle can be stopped and momentarily idled or shut off and both the fuel gauge and DTE meter will recover and again read levels accurately. Start the process over and again both read incorrectly as if the vehicle is nearly out of fuel.

I begain by replacing the fuel level sending unit with a fuel pump replacement thinking maybe it was having an issue. This had no effect on the continuing issue.

Next I checked the fuel tank vent valve and vent line for restriction by applying light air pressure at the purge solenoid line connection. Line was free and clear and air can be hear escaping from the fuel filler with the fuel cap removed.

I verified that the LDP works by unhooking a crankcase hose and driving the van. I immediately received DTC's related to evap leaks both small and large with no flow. Hooked the line back up, cleared DTCs, and they do not return.

I read about an issue where the fuel tank in another Dodge vehicle would either attempt to implode or blow up with pressure during operation causing the fuel level to read incorrectly. I operated the van with the fuel cap loose and the fuel gauge and DTE operated correctly.

I then moved back to the fuel tank vent line and now looked at the purge valve as the possible culprit. I removed the lower line from the purge valve which is the fuel tank vent line. The other line routes to the throttle body. I drive the van 30 miles with no issues from fuel level or DTE. Hooked the line back up for another 30 miles and the issue came back.

I replaced the purge valve believing it was not opening and that this was the problem. The issue remains. Only when I remove the vent line again does the issue stop.

I am now down to three scenarios.

1: The solenoid 2 wire harness is damaged and not supplying voltage to open the solenoid in turn causing either a vacuum or pressure to build in the tank and skewing fuel readings.

2: The ECM is damaged possibly by the old selenoid shorting out or the software is not triggering the purge valve to open causing the tank to build vacuum or pressure in turn causing fuel level issues. I say software because on another Dodge vehicle there was a software update that fixed this same issue.

3: Another valve or line is restricted somewhere else connected to the tank and is fighting the purge valve evacuation that uses engine vacuum.

Suggestions on my next move? Anyone have a wiring diagram for this system? Anyone know of a software update for this van?

 

Check the hose for the inlet filter for the leak detection pump - it’s near the brake booster and ABS module. A bulletin was issued regarding kinks in this hose resulting in the same problem you’re experiencing.

 

Will do!

 

Hose is straight and not kinked. Applied air to the LDP system and air comes out of the filter.

 

Right now, the only thing that stops the problem is unhooking this bottom line at the purge valve. I am about ready to put a hose connecting both lines and bypass the valve completely.

 

Bypassing the valve isn’t the fix - it may even make it worse.

The reason unhooking that line or removing/loosening the filler cap works to correct the problem is because it allows the tank and EVAP system to vent correctly. This indicates there’s something that should be venting but isn’t.

Have you gotten any codes for the EVAP system (P0440-P0449) except for leak codes (codes related to the control circuits for the vent or purge solenoids)?

If you’re confident you’ve ruled out any restrictions/kinks in the EVAP tubing, I recommend replacing the filler cap and see if that works. Your van should have a vented cap and if the valve in the cap is stuck shut (which wouldn’t be surprising if it’s the original cap) that could be the problem. They’re cheap and it’s an easy fix, if indeed that’s the problem.

 

No codes at all. My next step was to buy a cap tomorrow. They have two kinds. Emission and pressure vacuum. Im guessing pressure vacuum.

 

It would be the emissions cap.

 

Replaced the fuel cap with an emissions cap. No change. Tested the original fuel cap and the valve is working. Verified that the original purge valve is working correctly. Opens and closes to engine vacuum. Tested it on vehicle and got vacuum to the port. CEL comes on when unplugged and vacuum cuts off at port. Plug back in and clear CEL and vacuum comes back.

 

What do you mean “opens and closes to engine vacuum”? The purge valve should not be allowing vacuum through it at idle - part throttle while accelerating and at cruising speed only.