P0440 when it rains hard? - Toyota 4Runner Forum

The Cold War Kid · 11-26-2019, 10:58 PM

REALLY hard rain here the last few days. She threw a P0440 twice now, while being driven on the freeway in a downpour.

DUNZEL: Star Trek word for a part of a star ship that has no purpose.

In my perception, the evap system is a dunzel. It adds nothing to moving the truck down the road, stopping it or any other real function, of the truck. Maybe that's why I have paid it no mind, to date.

Would someone be so kind as to bring me up to speed on this dunzel? What is the most common cause of the P0440 code? How do we deal with it?

The truck has thrown this code only twice - both times in a heavy rain. Why?

jgue467 · 11-27-2019, 06:09 AM

Sounds like a short since water is involved so perhaps skip down to the electrical part of the list first?

FSM says about 0440 possible causes in easy to check order:
Hose or tube cracked, holed, damaged or loose seal ((3) in Fig. 1)
Fuel tank cap incorrectly installed
Fuel tank cap cracked or damaged
Vacuum hose cracked, holed, blocked, damaged or disconnected ((1) or (2) in Fig. 1)
Fuel tank cracked, holed or damaged
Charcoal canister cracked, holed or damaged

Electrical stuff starts here:
Open or short in vapor pressure sensor circuit
Vapor pressure sensor
ECM

Or the code can just be reset after a heavy rain.

Luck and enjoy the Runner.

The Cold War Kid · 11-27-2019, 07:44 AM

Quote:

Originally Posted by jgue467

Sounds like a short since water is involved so perhaps skip down to the electrical part of the list first?

FSM says about 0440 possible causes in easy to check order:
Hose or tube cracked, holed, damaged or loose seal ((3) in Fig. 1)
Fuel tank cap incorrectly installed
Fuel tank cap cracked or damaged
Vacuum hose cracked, holed, blocked, damaged or disconnected ((1) or (2) in Fig. 1)
Fuel tank cracked, holed or damaged
Charcoal canister cracked, holed or damaged

Electrical stuff starts here:
Open or short in vapor pressure sensor circuit
Vapor pressure sensor
ECM

Or the code can just be reset after a heavy rain.

Luck and enjoy the Runner.

Thanks for replying. Are these trucks known to throw this code when driven in heavy rain?

jgue467 · 11-27-2019, 01:04 PM

Yours is one of the few if only I've read of on here over the years. Anyone else?

I'd try pulling the electrical connections to the sensors, apply some electrical contact cleaner and finally apply dielectric grease to the contact points to seal them from future water invasion.

Luck and enjoy the Runner.

gamefreakgc · 11-27-2019, 02:54 PM

Quote:

Originally Posted by The Cold War Kid

Thanks for replying. Are these trucks known to throw this code when driven in heavy rain?

Our Nissan Altima throws an EVAP code when it rains really hard. Found out there's a breather hose that opens up to atmospheric air in the undercarriage and can suck up water from time to time. Once it dries or sits, code goes away. I just ignore it.

I would not be surprised if the 4Runner has a similar system, especially if yours is a 2001 or 2002 where the charcoal canister is located in the undercarriage near the spare like our Altima.

fourfive · 11-27-2019, 05:46 PM

I had this code a few years ago. Since yours is an 01 it's possible the overfill check valve on top of the gas tank might be the issue. After replacing that part on mine a few years ago I've been P0440 free. I did a fair amount of troubleshooting before confirming that part. It was such a small leak I had a hard time seeing it using a smoke machine. What gave me confirmation was occasionally hearing the faint sound of air escaping during the smoke test. I followed the FSM to test the evap system, charcoal canister, etc. It was a long tedious process.

P0440 Fixed!

negusm · 11-27-2019, 10:15 PM

Quote:

Originally Posted by jgue467

Yours is one of the few if only I've read of on here over the years. Anyone else?

I'd try pulling the electrical connections to the sensors, apply some electrical contact cleaner and finally apply dielectric grease to the contact points to seal them from future water invasion.

Luck and enjoy the Runner.

I have the same code currently. But not only in the rain. This seems to be a common code among 4Runners and Tacos.

The Cold War Kid · 11-28-2019, 09:20 AM

Quote:

Originally Posted by negusm

I have the same code currently. But not only in the rain. This seems to be a common code among 4Runners and Tacos.

From my reading it seems likely to be a leaking filler tupe/gas cap or a little valve on top of the tank. I think mine may be a leaky connection for the wiring to the sensor...

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