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Q: Vehicle stalled at 75mph after 30 minutes of driving. Code for pump. Gauge said 1/8th but tank was dry.

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No previous loss of power, missing, or other problems. I did reset the computer to no avail. Garage said it pulled code for fuel pump, but I won't have the code until Monday. I'm suspecting at least a fuel gauge relay, to address the inaccuracy. Once the car was filled up 1/2 it was running again. If the pump had failed I would expect some difficulties with starting that aren't present. I'm suspecting I have some residue or debris in the lines or the tank itself- causing the relay issue and potentially damaging/impacting the pump. I will replace the fuel filter for good measure. I don't trust the garage (who wanted to order a new dash unit because I have an LED range in the DIC)... I'm not sure if they can test the pressure (they may not be equipped)... I'm handy but I don't have a lift. Should I have the lines flushed? I'm concerned about doing damage to the engine if I drive it before this is resolved. What's the most cost effective way to approach this? Thank you!

My car has 72412 miles.
My car has an automatic transmission.

A: Most likely the problem is the sending unit...

Most likely the problem is the sending unit in the fuel tank. A fuel gauge relay will not create a wrong gauge reading. Fuel pumps come as modules that include the fuel level sending unit. In most cases it is best to replace the complete module and not just the sending unit. This will be determined by the options available from the parts house, but most newer GM cars require the replacement of the entire module, especially in the case of the sending unit.

Before you go and replace the module though, I highly recommend you find someone that can do an accurate diagnosis. The most common failure may be the sending unit, but gauges do fail as well. I would begin by connecting a scanner to read the data and see if any codes are present. I personally have a resistance box that I can use to test the gauge with. Using a resistance box is the most accurate way to test the gauge. The sender can be tested by using a ohm meter and adding fuel until the tank is full. Both of these tests require information about their prospective resistance values, not to mention this can be challenging to know where to do these tests.

The only reason your car is dying is it is running out of fuel due to an inaccurate gauge reading. The question is, is it the gauge or the sender. I recommend contacting customer service to see if there is a technician in your area with the necessary expertise to accurately diagnose your car.

To add, I see no need to flush out your fuel lines. A good service that I do recommend is an injector cleaning done with a machine and not just something you poor in the tank. You can inquire with YourMechanic's customer service to see if we have a tech with this capability as well.

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