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Here's What You Need to Know if You Accidentally Put Diesel Exhaust Fluid in the Fuel Tank

The consequences can be dire when the diesel fuel is contaminated with DEF. In the more severe cases, the entire fuel system must be replaced, from the fuel fill pipe to the fuel injectors and everything in between.
Here’s what you need to know if you accidentally put diesel exhaust fluid in the fuel tank 6 photos
Here’s what you need to know if you accidentally put diesel exhaust fluid in the fuel tankHere’s what you need to know if you accidentally put diesel exhaust fluid in the fuel tankHere’s what you need to know if you accidentally put diesel exhaust fluid in the fuel tankHere’s what you need to know if you accidentally put diesel exhaust fluid in the fuel tankA 1.5-liter and a 10-liter AdBlue container
Diesel exhaust fluid, also known as DEF, AUS (from aqueous urea solution), or AdBlue, is used to lower the concentration of NOx in diesel exhaust emissions. Usually, the DEF tank filler is placed right next to the fuel filler. This can sometimes confuse users to put DEF into the fuel tank. Such a mistake could be more expensive to fix than filling the tank with gasoline instead of diesel fuel.

As with other mistakes, being aware of it as soon as possible can significantly help limit the damages. If diesel fuel gets mixed with DEF, it may cause damage to the engine and the fuel system. These are not covered by the vehicle’s warranty, so you better act as soon as you discover the mistake. The best results are expected if you stop right before putting the key in the ignition.

If you never touch the ignition, the in-tank fuel pump has not started. In this case, the damages are limited to the fuel fill pipe, tank, and fuel pump module. Those three will need to be replaced to avoid more severe problems down the line. As you can see, this is already pretty expensive, so you better watch out when you fill that DEF tank.

If you put the key in the ignition but did not start the engine, the fuel pump may have begun to pump fuel. This means that the contaminant starts traveling, causing further damage. In that case, the system from the fuel fill pipe to the high-pressure fuel pump and the high-pressure pipe from the pump to the rail must be replaced along with the low-pressure return lines.

But the real mess happens if you have already cranked the engine. Then the entire fuel system needs replacement. In addition to all the parts listed above, you will have to replace the fuel rail, injectors, and injector return fuel lines. GM TechLink explains what happens if you mix DEF with diesel fuel. In the case of the fuel pump module, the steel and aluminum parts will start corroding. At the same time, a crystal-like residue will form on the outside, which can lead to some parts like the terminals fracturing or breaking.

 
 
 
 
 

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