How To Replace Diesel Exhaust Fluid And A Diesel Particulate Filter

Diesel fuel is not the only fluid your diesel vehicle needs to run. It also requires something called diesel exhaust fluid (also called DEF). Just like when the fuel tank is empty, your engine won’t start. The same thing will occur if your DEF tank runs dry. So it’s really important to keep an eye on the diesel exhaust fluid tank if you don’t want to be stranded on the roadside.

The DEF pump and the diesel particulate filter also need a bit of attention. You need to ensure that they play their part in keeping the Selective Catalytic Reduction (SCR) system clean. In this guide, we'll show you how to replace the following parts in your GM vehicle's SCR system:

  • Diesel exhaust fluid
  • Diesel particulate filter (DPF)

If you're looking for a tutorial on replacing your GM vehicle's DEF pump, we have one here.

What Is Diesel Exhaust Fluid And What Does It Do?

DEF fluid cap

Diesel exhaust fluid (DEF) is a liquid solution of urea and de-ionized water. This liquid is injected into the exhaust system. It's used to neutralize the harmful nitrogen oxides in the exhaust gases and break them down into harmless elements. The harmless elements are nitrogen and water. DEF is stored in a specific tank that is separate from the gas tank. If you want to read more about what DEF is and how it works, check out this post.

What Is A DEF Pump?

Image Credit: LehewTech

A diesel exhaust fluid pump is mounted to the top of the DEF tank (which contains the fluid). The pump is submerged in the DEF. Its job is to pump the fluid into the exhaust system. Without a functioning DEF pump, your vehicle's exhaust system can't get any DEF.

An OEM GM DEF pump comes with a screen on the inlet. It filters the fluid before sending it into the SCR system. Here's a tutorial on replacing a DEF pump in a GM vehicle.

What Is A Diesel Particulate Filter?

A diesel particulate filter (DPF) is a ceramic filter located within the exhaust system. It's made up of tiny channels containing precious metal elements that filter out diesel soot. Its role in the SCR system is to remove the harmful particles and gases from the exhaust fumes.

This filter is self-cleaning (using a process called regeneration). Yet, you still need to replace it at certain intervals. This may be due to damage to the DPF, or to natural wear and tear. Under normal circumstances, an OEM GM DPF starts to fail after 70,000 miles.

What Tools Do I Need For The Job?

Replacing the DEF and the DPF are two separate jobs. One does not require any specialist tools, whereas the other one requires a decent toolkit amongst other items.

To replace the DEF, you will need:

  • A small funnel
  • Latex gloves

To replace the DPF, you will need:

  • A hydraulic jack
  • Jack stands
  • A car creeper
  • An inspection lamp
  • A full set of spanners or a good socket set
  • A full set of screwdrivers
  • Gloves (it’s so much more pleasant to work without getting dirty hands or cuts)

Replacing The Diesel Exhaust Fluid

Adding diesel exhaust fluid

First, locate the filler of the DEF tank. Depending on the make and model of your vehicle, this may be under the hood or next to the gas tank filler. If the DEF tank filler is next to the gas tank filler, it will be the smaller of the two. Usually the DEF filler is blue. Take the following steps:

  1. Put on your gloves.
  2. Open the filler.
  3. Place the funnel in the filler. This will avoid any spillages, since DEF is corrosive.
  4. Fill the tank with the DEF (often marketed under the name “AdBlue”) until full.
  5. Remove the funnel and replace the filler cap.

That's all! It's a pretty easy and straightforward process.

WARNING: If you accidentally pour DEF into the diesel tank, DO NOT start the engine. This may damage the fuel circuit and diesel injectors. Have the vehicle towed to a workshop to have the fuel tank drained and cleaned.

Replacing The Diesel Particulate Filter

First, you need to order a replacement DPF. You can check out our selection of genuine OEM diesel particulate filters here. We offer the lowest transactional prices you'll find online. Please contact us if you need help finding the right DPF for your diesel vehicle.

Once you have your replacement DPF on hand, take the following steps to replace the DPF on your GM vehicle.

Preparing Your Vehicle

  1. Put on some mechanic's gloves because this can be a messy job.
  2. Jack up the front of your vehicle and then lower the vehicle using the jack until it is resting on the jack stands. You will be working under your vehicle for quite some time. So make sure that the jack stands are appropriate for its weight, and that they are correctly and securely positioned under the vehicle.
  3. Slide yourself under the vehicle with the car creeper.
  4. Place the inspection lamp in a way that will light up the part of the vehicle you’ll be working on without dazzling you.

Removing The Old DPF

Find the DPF and then loosen and remove all the bolts and other fasteners holding it in place. The size of the bolts and fasteners will vary depending on the make and model of the vehicle. When all the bolts and fasteners have been removed and safely stored away, remove the DPF.

PRO TIP: If you have never replaced a DPF before, take photographs (with your cellphone, for example) as you remove the DPF. This will help you to correctly fit the new filter and all the necessary bolts, screws and fasteners.

Installing The New DPF

Fit the new DPF and ensure that it is pointing the right way. DPFs have a flow direction. If you fit the filter the wrong way round, you can cause serious damage to the filter and to the engine.

Next, replace and tighten all the bolts, screws and other fasteners. Once they are correctly tightened, ensure that the DPF doesn’t have any play.

Slide out from under the vehicle and raise it using the hydraulic jack. Remove the jack stands and carefully lower the vehicle until the front wheels are on the ground again. Before lowering the vehicle, make sure that all tools, parts and any other objects are not under the vehicle.

WARNING: DO NOT attempt to replace the DPF if the engine has been running. The filter, like the rest of the engine and exhaust system, gets very hot and can cause serious burn injuries. Only handle the filter when the exhaust, filter and engine are cool to the touch.