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Honda Civic Service Manual: Fuel Supply System Leak Inspection (R18A9)

Honda Civic Service Manual / Powertrain / Engine / Fuel System / Fuel Supply System Leak Inspection (R18A9)


Compressed natural gas is flammable and highly explosive. You could be killed or seriously injured if leaking natural gas is ignited.
Stop the engine, and keep heat, sparks, and flames away.

1. Fuel Supply System Leak - Inspection (Natural Gas Model)

Check for a gas leak if there is an odor coming from the vehicle. Compressed natural gas (CNG) can only be smelled, not seen.


Open the hood and the fuel fill door.


Connect a vacuum pump/gauge, 0-30 inHg, to the hose (A) from fuel pressure regulator P1, and apply 67.7 kPa (20.0 inHg, 508 mmHg) of vacuum.


If fuel pressure regulator P2 does not hold vacuum, replace it before continuing to the next step.


Inspect the fuel lines and hoses under the hood for kinks, abrasion, and other signs of damage.


With the manual shut-off valve open, turn the ignition switch to ON (II), but do not start the engine.


After the fuel pressure regulator shut-off solenoid valve/fuel tank internal solenoid valve operates for about 2 seconds, the fuel pressure in the fuel lines rises.


Turn the ignition switch to LOCK (0).


Repeat this two or three times.


Within 1 minute, check for any damaged lines with a leak detector (A) (Snap-on Combustible Gas Leak Detector or Snoop Liquid Leak Detector (B)).


If no damage was noticed during the inspection, turn the ignition switch to ON (II) for 2 seconds, then turn the ignition switch to LOCK (0).


Within 1 minute, check for a leak at the vent hose outlet inside the fuel pipe protector (A).


If you detect a leak, remove the vent hose, and check the fuel lines and fittings at the in-tank solenoid valve and the join block with a leak detector.


If you cannot find the leak, raise the vehicle on a lift, remove the under-floor cover.


Inspect all the fuel lines under the vehicle, visually, and with a leak detector.


If you still cannot find the leak, remove the rear seat, then check all fuel lines and fittings at the fuel tank and the fuel joint block.

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Manual Shut-off Valve Removal and Installation (R18A9)
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