Mysterious issue with a 2020 Subaru Forester
Hoping anyone out there has any ideas our dealership doesn't.
Timeline:
- The car was running rough.
- Brought to the dealership.
- Transmission fluid found to be dirty, changed by dealership.
- Car still running rough.
- Check engine light comes on.
- Dealership finds code P1449, and finds that the entire evaporative emissions system has failed.
- Dealership replaces evaporative emissions system.
- Car returned, runs perfectly.
- But the check engine light comes on a few minutes later.
- Dealership finds the same code, P1449, and from six key cycles ago, from before it was picked up at the dealership.
- The dealership says this is a "ghost code", from before the evaporative systems repair, and clears the code.
- Check engine light comes on again.
- Brought back to the dealership, they say it's the same code again and are mystified.
- They clear the code, drive the car for 120 miles over several start-stop cycles and cannot get it to happen again.
- We pick up the car, and the check engine comes on again a few miles down the road.
Anybody have any ideas? What could we be doing that they are not that could cause this?
Posted Sep 2, 2022, 1:39 AM UTC
11
that's not really a thing. Maybe you meant the ELCM assembly?
The "entire evap system" includes the gas tank, all the lines between the tank and the engine, the charcoal canister, the ELCM.... I definitely doubt they replaced all of that. Do you happen to have the receipt from when it was done? There might be a parts listing on the copy of the work order, should also have the technician's notes as well.
Normally I'd refer you to the parts diagram, but it would appear there is no diagram for your year here, so uhh, to the service manual we go I guess. Here's a pair of diagrams from the manual.
Part number 1 in the first diagram is the ELCM, or Leak Check Module. In there is a little vacuum pump and a pressure sensor. If you've ever gone out in the garage at 2AM and heard what sounds like a little electric motor buzzing away, this is what's making the noise -- it's putting the fuel system under a vacuum, and then watching the pressure sensor to see if a leak is detected.
In order to do this test properly, it needs to have a way to allow air back in when complete. That air inlet is the part I put a red arrow to - it's a filter assembly, with a hose that leads down to the ELCM.
That filter is located inside your passenger rear wheel well arch, kind of rearward of the gas door -- you can access it by removing the clips that hold the wheel well liner in.
Every case of P1449 I've come across personally, has been caused by mice nesting in the wheel well liner and blocking off the filter inlet.
this code is never going to cause a running issue -- it just means your EVAP system testing fails. According to the diagnostic tree for the code, the car needs to run the test (and fail it) twice in a row to turn on the CEL, so clearly the dealer isn't force-running a system test and checking for pending codes.