Gasping fuel tank

[Peter Bryenton]

Hi All.

Is it normal for my 2003 RAV4 Auto-box 3-door to suck air in hard when I remove the petrol filler cap to refuel? I ask this because the engine light comes on (orange) after having used about 3/4 of a tank full. When it has been re-filled to full-up, I drive away from the forecourt to find that the engine light has gone off all by itself. The cycle repeats.

If I connect a cheap basic code reader it displays "No faults" but it won't let me reset the engine light.

The car drives very smoothly and averages around 8.6L/100Km. That seems OK to me for a 2L engine with 175,000 miles, nearly 20 years old. Regularly serviced and maintained by a reputable professional engineer.

[Roy124]

Fuel tanks need air vents or else the tank could collapse on itself as fuel is sucked out.  We had a tank collapse on an old BL utility.  Modern tanks may be stronger. 

You may have a vent blockage.  The vent may be in the filler receptacle. 

[philip42h]

You might want to start by replacing the fuel filler cap:

The engine light will come on if the filler cap is loose or missing. As I understand the tank should have a positive pressure and this is controlled by the breather in the cap. So I'm guessing that the negative pressure you report would trigger the light. But it would be cheap to simply replace the cap.

[Peter Bryenton]

My thanks to Roy and Philip.

I'll start today by replacing the filler cap.

[yossarian247]

On cars with evaporative emission control (ie any petrol built in the last 25+ years) I thought it was intentional for the filler cap to be totally sealed with no breather? The venting of the tank is then done via a charcoal cannister with a certain amount of negative pressure being totally normal. The amount of negative pressure is regulated by the emission control system. I don't think the filler cap is at fault here.

[Peter Bryenton]

That's interesting, thanks Nick. I'm not a tecchie but it is clear to me as a novice that the engine management system "knows" something about what is happening in the petrol tank.

 

I'll start with a "clean slate" by fitting a brand new OEM filler cap for £20. That way it should be at least possible to eliminate any symptoms which may have been the result of age-related deterioration in the old one. The recurring costs of specialist diagnostics is becoming prohibitive for such an old -- but mostly reliable -- vehicle, especially on my retirement income!

[yossarian247]

I'm surprised your code reader won't read and clear the code? Being a 2003 petrol car (your profile says 2013 by the way?) it should be EOBD compliant so any code reader ought to work.

[IanML]

I think it likely you have a faulty charcoal canister, or perhaps the associated valve.  As Yossarian said, the system is designed to hold a vacuum, to prevent emission fumes getting out without passing through the filter.  

Having said that, the warning lamp should be accompanied by a diagnosed fault number.  Your basic code reader may be incapable of displaying it.  You could get a copy of Toyota Techstream (runs on a laptop) together with the associated special lead, on eBay.  Usually, the software is free with the lead (or vice-versa). Techstream will report historic faults, even if the symptom has cleared.

[Peter Bryenton]

Code reader(s): thanks to Nick and Ian. I'll edit my profile. I will investigate if that software will work on a Chromebook.

[ernieb]

I think Techstream is Windows based so not sure if you’d be able to run your Chromebook. I generally run Mac or MacBook but keep a windows based laptop for these situations.

[Peter Bryenton]

Thanks Ernie. Yes, Chromebooks are limited for specialist software. I have been told that there are bluetooth OBD2 units and apps for smartphones.