Cars sometimes hit you with problems that just can’t be ignored. A jammed gas flap has happened to me more than once, but then I drive classic cars, so you expect these types of challenges.
Gas flaps have a secret emergency release handle fitted in the trunk behind the cover. Pulling the release opens the gas flap.
In this post, I’ll show you how to locate and operate your emergency gas flap. I’ll explain the different types of systems and list their common faults.
Locating & Using Gas Flap Release
If your car has a gas flap that locks, you’ll have an emergency release handle. The finding is usually pretty easy, remember they’re designed to be used in an emergency so you won’t need tools to access it.
In all cases, the release will be fitted inside the vehicle. Most likely in the trunk. Accessing it usually involves peeling back some trunk wall carpet to reveal the release. If you’re having difficulty finding yours, check your driver’s manual or a google search for your vehicle type.
The release handle may be fitted on the interior side of the gas flap assembly or fitted remotely. The release handle itself is sometimes marked by a brightly colored tab, but if not it should still be fairly obvious.
To operate the release just pull on the handle. You’re free to close the gas flap after filling it with gas, the emergency release can be used repeatedly.
Types Of Gas Flap Release
On older cars, the gas tank filler neck was fitted to the outside of the vehicle. This seemed like a good idea at the time but presented a few problems.
The most serious was in the event of a vehicle turning over, the gas cap could strike the ground causing a leak and a fire. Less serious was gas theft and dirt on the gas filler cap and tank neck.
The solution – recessed the cap from the outer body panels and fit a flap. In the beginning, the flaps were not locked, that was a later evolution.
Common gas flap locking systems include:
- Cable operated
- Air operated
The cable-operated system is the simplest of all. The flap is spring-loaded and when closed is caught by a latch. The latch is connected to a braided cable, not unlike a bicycle brake cable and is connected to a lever close to the driver’s seat.
The air-operated locking system then became popular. The gas flap was integrated into the central locking system, where locking the doors also locked the trunk and gas flap.
The motorized gas flap is the norm today. Car electrical systems are dominated by control modules (Computers) and have been for the last twenty years. It makes sense for manufacturers to replace manual controls with actuators (motors that move a component). Control modules use power and resources efficiently and offer self-diagnoses.
Common Gas Flap Problems
Here we’ll look at each of the systems in a little more detail. As the gas flap locking and releasing types vary so too will the common faults. If your car is less than twenty years old, you’ll likely have an electric motorized gas flap, it’s the most common type and the one we’ll look at first.
Motorised Gas Flap Common Problems
You already know that your car is run by various control modules. You have probably heard of the ECM (Engine Control Module) aka PCM, it manages the engine. The gas flap doesn’t have a dedicated controller, instead, it will likely be controlled by the body control module or the central electronic module or possibly a central locking control module.
A locking gas flap is incorporated into the locking system. Unlocking the car also unlocks the gas flap. If your passenger doors are unlocking without issue then your gas flap should too. If however, your passenger doors aren’t opening, the problem may lie with the central locking module and not the gas flap itself.
Troubleshooting your problem should begin by gathering as much info about the fault itself. For example, did this problem coincide with changing a flat wheel, fitting any accessories or bad weather events, etc?
Or did any other functions of the car fail at the same time? Some cars may lock the rear doors, trunk, and gas flap independent of the front doors. That type of fault would point to a module issue and not your gas flap.
This is the type of detective work that will help isolate the problem.
Common issues include:
- Flap lock binding
- Faulty flap lock motor
- Faulty flap lock motor wiring
- Faulty control module
A binding flap lock is very common. If for example, an enterprising thief tried to force the flap open, the locking pin may bend and fail to retract fully when unlocked.
Retracting the lock by hand removing the pin and straightening will fix this issue. To test for faulty flap lock motor, check for power at the gas flap when you unlock the car, follow these simple steps.
What you’ll need for this test:
A test light, or Voltmeter
- Gain access to the gas flap motor.
- Lock the trunk latch (car wont lock with latch open).
- Using a volt meter or test light, check for power at the wiring as you lock and unlock the car.
A reading of 12v or a light tells you the motor is getting power, and if it’s not binding, your motor has failed.
If you found no power at the wiring, read on. Test for faulty flap lock wiring – If you don’t have any voltage, you may have a wiring or a module fault. Go ahead and check power and ground independently.
Air Operated Gas Flap
The air-operated central locking system including gas flap was common during the ’80s and 90’s cars. It operates by having an air pump usually in the trunk or under the rear seat pump air through plastic pipes to the diaphragm actuator.
Pumping air to the activators unlocked the flap and reversing the motor to produce vacuum locked the flap. An activator with its own pipework was fitted to door locks, trunk, and gas flap lock. If your door locks aren’t locking/unlocking as normal, diagnose that problem before looking at the gas flap lock.
Common problems with this type of system include:
- Binding flap lock
- Damaged air supply pipe
- Dry rotted rubber air supply fitting
- Faulty actuator diaphragm
A binding flap lock is common. If for example, an enterprising thief tried to force the flap open, the locking pin may bend and fails to retract fully when unlocked. Retracting the lock by hand removing the pin and straightening will fix this issue.
Checking air supply pipes is easy, this system is simple to troubleshoot. If all other doors are locking and unlocking then it’s most likely an issue with the air supply or the actuator.
- Locate the flap assembly and check the pipework is in place.
- Lock the trunk latch (allows you activate the central locking)
- Remove the pipe and check for air and vacuum as you lock and unlock the car.
No air suggests a damaged pipe or connector further up the line towards the pump. If, on the other hand, you have air, the diaphragm actuator has failed, replacing will fix the problem.
The diaphragm actuator is a simple air-tight cylinder that moves a metal lever arm. You can test it by blowing air into the port and watching the rod lever move, applying a vacuum should retract it.
If it doesn’t work, you found your problem.
Cable Operated Gas Flap
The cable-operated gas flap is the easiest of all to problem solve. Common problems include:
- Binding flap lock
- Broken braided cable
- Detached braided cable
The problems with this system really don’t need much explanation. Check the following:
- Cable connected at flap release control (drivers compartment).
- Cable connected at the flap lock assembly (trunk).
- Check if cable is broken.
Pry open a gas tank door? Prying open the gas tank door is not required. Instead use the emergency gas door release handle hidden in the trunk, behind the gas door assembly.
- About the Author
- Latest Posts
John Cunningham is an Automotive Technician and writer on Rustyautos.com. He’s been a mechanic for over twenty-five years and has worked for GM, Volvo, Volkswagen, Land Rover, and Jaguar dealerships.
John uses his know-how and experience to write fluff-free articles that help fellow gearheads with all aspects of vehicle ownership, including maintenance, repair, and troubleshooting.