Jim Grant's Tech Tips

‘96 Honda Civic, Gas Cap or Problems?
Q:# I have a ‘96 Honda Civic CX. The engine light came on. Honda service read the computer code, reset the engine light for $34. They told us it might be a defective gas cap or improperly sealed cap and advised us to make sure it is sealing properly by turning it until we hear the clicks. Within a week, the engine light came on again. Honda service read the code, same code as before. Reset the engine light for another $34. They changed the gas cap for a new one just to make sure. $13 + tax. The engine light has just come on again. #1: Is there a way to check if the gas cap was/is defective in the first place? When we remove the cap, we hear a distinctive whoosh of built up pressure. Should this not confirm that there is no leak around the gasket or anywhere else? #2: Is there a way to check the pressure transducer? If so why did they jerk me around thinking it might be the cap? #3: Why is it important to measure this gas pressure information? Can I ignore this error condition? #4: Can I check these codes and reset the computer myself? Someone said I could do it with a simple module. I might even be able to see this information via a serial port using a computer/laptop and diagnostic software. I would appreciate any help you may give me in this matter.

A: # 4. Yes you can check your vehicle’s computer for Diagnostic Trouble Codes (DTC’s) and reset the computer yourself with a lap top computer. Search the internet with key word (OBD II). This will take you to many sites that sell such equipment.
#3. Yes it is important to monitor gas pressure. Why? If a vehicle’s gas tank is not sealed properly, the volume of raw Hydrocarbons HCs that escape into the atmosphere exceeds what comes out the tail pipe of your vehicle many times. Yes, today’s vehicles are that clean out the tail pipe. By monitoring the pressure in the gas tank the vehicle’s on-board computer can identify an evaporative system failure. The evaporative system is more than a gas tank and cap. It also incorporates a charcoal canister, hoses and tubing that travel the full length of the vehicle, computer controlled/monitored solenoids and pressure sensors.
#1 & 2 As for the jerk around, all I can say is when one of our customers come in with a light on and no driveabilty complaint we ask if the vehicle has been fueled up recently. Why? Because the gas cap may not be tight enough. This has happened a lot and we’re just a small town garage. We check and demonstrate proper gas cap installation and close with the recommendation that the vehicle be driven for a few days at no charge for our time educating the customer. The alternative is plugging in and charging you for the computer scan tool, plus labor time to go through a factory diagnostic procedure, monitor the pressure sensor etc. (takes more time than you can image) to tell you that the gas cap was loose. Many areas have or are in the process of implementing (including New Hampshire) emissions testing that requires checking the computer on ‘96 and newer vehicles.. This is only the tip of the iceberg, there is so much more to explain. As a consumer you have so much more to learn. I’m sure there will be more discussion in this area.