What is a gas cap sensor?
A gas cap sensor, also known as an EVAP system pressure sensor, is part of a vehicle’s Evaporative Emissions (EVAP) system. The EVAP system prevents fuel vapors from escaping into the atmosphere from the fuel tank and fuel system. The gas cap sensor specifically monitors the pressure and vacuum inside the fuel tank to detect leaks or issues with the gas cap not sealing properly. It communicates this data to the vehicle’s on-board computer system.
Why do you need a gas cap sensor?
The gas cap sensor is an important emissions monitoring component in modern vehicles. It allows the vehicle’s computer to detect issues with fuel vapor leaks early, triggering the check engine light to alert the driver. This allows the driver to address small leaks before they become large evaporative emissions problems. A missing, damaged, or faulty gas cap sensor will cause the check engine light to illuminate and often triggers an evaporative emissions code such as P0442, P0455, or P1450. Replacing the sensor restores proper monitoring of the EVAP system.
What are the symptoms of a bad gas cap sensor?
Some common symptoms of a bad or failing gas cap sensor include:
- Check Engine Light comes on – This is often one of the first signs of an issue with the gas cap sensor. The on-board computer detects inconsistent pressure readings.
- Fuel odor present – Small evaporative emissions leaks or a loose gas cap may cause noticeable fuel vapors/smell from the rear of the vehicle.
- Difficulty refueling – A faulty gas cap sensor can cause issues with properly sealing the fuel system, leading to difficulty refueling or longer fill-up times.
- Failed Emissions Test – Larger evaporative emissions leaks can cause the vehicle to fail an emissions test. The gas cap sensor is a key emissions monitoring component.
If any of these symptoms are noticed, it’s a good idea to have the gas cap sensor inspected by a professional technician.
How much does a gas cap sensor cost?
Gas cap sensor replacement costs typically range from $135 to $280 for parts and labor. The part itself usually costs between $25 and $110 depending on the vehicle make and model. Here are some more details on average gas cap sensor replacement costs:
- Labor costs – 1 to 2 hours of labor are typically required to replace a faulty gas cap sensor, at an hourly shop rate of $90 to $150. This results in $90 to $300 in labor costs.
- Part costs – The gas cap sensor part can range from $25 to $110. More expensive luxury and hybrid vehicles tend to be at the higher end.
- Total costs – Combining labor and parts, total replacement costs end up between $135 and $280 on average. Domestic vehicles tend to fall under $200, while imports may cost over $200.
There are some ways to help minimize replacement costs. Shopping around for the best labor rate, using high quality aftermarket parts, and buying the part yourself online can potentially reduce the overall sensor replacement costs.
When should the gas cap sensor be replaced?
The most common reason to replace the gas cap sensor is when it has completely failed and is no longer providing accurate pressure readings to the vehicle computer. Symptoms like consistent check engine lights, evap codes, and emission test failures indicate complete sensor failure.
However, sometimes the gas cap sensor may only have partially failed. Intermittent check engine lights or fuel vapors may indicate the sensor is still functioning at times. In these cases, replacement may not be immediately necessary. The sensor and connections can be further diagnosed and cleaned to see if operation improves before replacing.
Preventative replacement is usually not required. Gas cap sensors often last upwards of 100k miles or more. But some vehicle manufacturers do recommended replacement once the sensor reaches a certain age or mileage to maintain optimal EVAP system monitoring.
Can you drive with a bad gas cap sensor?
In most cases, it is possible to drive with a bad or failed gas cap sensor. Since the sensor does not directly affect engine operation or drivability, the vehicle will still start and run. However, driving with a faulty sensor can lead to a few issues:
- Check Engine Light stays on – Continuing to drive with the check engine light caused by a bad sensor will not damage anything, but the light will remain on.
- Potential increased emissions – Larger evaporative emissions leaks could develop over time if not detected early by a working sensor.
- Emissions test failure – The check engine light will cause an immediate emissions test failure in most areas.
While not an immediate safety issue, the EVAP system issue should still be diagnosed and repaired promptly. Continued driving without repairing the sensor can potentially lead to the vehicle exceeding emissions limits.
Can a gas cap sensor be cleaned or reset?
Sometimes a gas cap sensor will suffer from intermediate failure rather than a full failure. In these cases, cleaning or resetting the sensor may temporarily restore normal function and turn off the check engine light. Some things to try include:
- Clean sensor contacts – Clean the electrical sensor contacts with electrical contact cleaner spray and rag.
- Check sensor wiring – Inspect wiring to the sensor at the fuel tank for damage, corrosion, or looseness.
- Clear engine codes – Use an OBD2 scanner tool to clear any stored evap system codes.
- Perform sensor reset – Some scan tools allow performing a sensor reset to clear its history and restore normal function.
- Tighten/replace gas cap – A loose or damaged gas cap can sometimes trigger an intermittent sensor code.
If cleaning and reset procedures do not resolve the issue, then a full gas cap sensor replacement will be necessary. But cleaning/resetting the sensor is an easy first step before spending on replacement.
Conclusion
A failed gas cap sensor will trigger the check engine light and requires replacement in most cases. Replacement costs for the sensor average $135-$280 for parts and labor. Prices depend on the vehicle and local labor rates. While not an emergency repair, driving with a bad gas cap sensor should be avoided to prevent excess evaporative emissions. In some cases, cleaning and resetting the sensor may restore normal operation. But a full replacement of the gas cap sensor is eventually needed for long term repair.