Troubleshooting problems with a Fuel Pump Relay is usually about going through the motions, trying to pinpoint whether a relay failure exists that’s causing the problems with fuel delivery. Difficulty in engine start-up and intermittent engine stalling due to inability of the Fuel Pump to get power continuously are usually the first telltale signs of a failing relay. First, start by consulting a diagram in the vehicle’s fuse box that indicates the location of the Fuel Pump Relay, which is generally located in the main fuse box or a separate relay panel. This is a vital step since the location will vary from one model of vehicle to another.
Once located, visually inspect the relay for obvious signs of damage such as burn marks or corrosion, which can affect the electrical contacts. Corrosion is one of the more common reasons for malfunction and especially occurs with higher mileage vehicles or those subjected to poor environmental conditions. If visible damage is present, replacement may be necessary since these types of issues are generally irreparable.
The next step would be to use a multimeter and check the voltage and continuity of the relay. A good Fuel Pump Relay should read 12 volts once the ignition is turned to the “on” position. If the multimeter reads no voltage or shows inconsistent readings, the relay is definitely bad and should be replaced. The Fuel Pump Relay should really last between 5 to 10 years, in most instances, depending on the vehicle and environmental factors. However, corrosion or wear can easily shorten its life.
Swapping the relay out with one from a non-critical system (in other words, something less than lights or horn) on the vehicle can also be helpful in determining if the problem is with the relay or another component. If this indeed fixes the starting problem, then it confirms that the relay was bad. The replacement cost for a faulty relay is generally low, ranging between $10 and $30 on most vehicles.
In some cases, it may also involve checking the Fuel Pump itself because, sometimes, a faulty Fuel Pump can give symptoms that relate to a bad relay. For instance, if the Fuel Pump is drawing too much current or has an internal short, it will prevent the relay from working as it should. In these cases, further examination of the Fuel Pump includes fuel pressure and electrical checks. Generally, problems with the Fuel Pump Relay can take as short as 30 minutes or as long as a couple of hours to fix, depending on how complex the electrical system is on the car and if replacement parts are available.