Renault has been using Selective Catalyst Reduction (SCR) exhaust gas treatment systems with its diesel engines since approximately 2009 in various models. SCR technology significantly reduces nitrogen oxides in the exhaust gas. Renault's system runs the engine with a minimal amount of oxygen possible in order to reduce NOx without degrading performance and fuel economy.

There are 6 primary elements to the Renault aftertreatment system which includes : -

  • Diesel particulate filter
  • Diesel oxidation catalyst
  • Exhaust gas recirculation system
  • Selective catalyst reduction system
  • Lean Nox trap
  • Catalytic convertor ( petrol powered engines)

Renault’s suffers from EGR valve, cooler and intake soot issues like most diesel vehicles on the market. Throw in DPF issues just for good measure if you are just pottering around the burbs at lower speeds as well. If SCR isn’t properly maintained on older vehicles it can cause grief as well.

Diesel Particulate Filter (DPF)

All Renault diesel powered have a DPF fitted to help in the reduction of harmful contaminants being expelled into the atmosphere. The soot emitted by diesel engines is particularly harmful to people who suffer with respiratory illnesses such as asthma, bronchitis and emphysema.

Over time the DPF can become blocked with a residue of ash from the soot trapped in the filter being burnt off in a process called regeneration. Periodic maintenance is required to keep the DPF functioning correctly which in turn will keep the running costs of your Renault’s low, maintaining performance and reliability.

Exhaust Clean Australia are your experts in DPF cleaning with our revolutionary, market leading equipment ensuring clean emissions and trouble-free motoring. When you or your mechanic send your DPF to us for a clean please ensure that the sensors aren’t removed as we will clean them as part of the service for no extra charge!

Nitrogen Oxide Trap

The new NOx trap works in two phases: It captures NOx for 10 minutes/10 km, obtaining a Ba(NO3)2 solution which can be safely transformed into N2. The latter is released to the atmosphere once the engine is working at a rich-burn mode which allows complete combustion. Compared to the AdBlue systems used by German automakers, this system is closer to Honda's D-CAT NOx trap.

This chemical process captures harmful nitrogen oxides, then converts them into neutral gas. The new NOx Trap with catalytic converter has a dual function:

  • - the traditional function of oxidising hydrocarbons (produced by partial combustion) and carbon monoxide (produced by partial combustion due to a lack of oxygen);
  • - the treatment of nitrogen oxide (produced by the combustion of diesel fuel at high temperatures).

How the NOx Trap works

The NOx Trap operates by capturing and storing NOx (for 10minutes/10km) then releasing it – a five-second process not noticeable by the driver.

During the capture phase, the NOx Trap traps the nitrogen oxide contained in the exhaust gas on a porous carrier in the catalytic converter which is impregnated with chemicals – platinum, barium, rhodium. The platinum converts nitrogen oxide into nitrogen dioxide (NO2). The barium, which oxidises into barium oxide, traps and holds NO2 as part of an aqueous barium nitrate solution – Ba(NO3)2.

In the release phase, a chemical process known as reductive elimination purges the NOx Trap of the stored NOx, with the engine operating in rich-burn mode, i.e. when the air-fuel mixture has just enough air for complete combustion of the diesel. The nitrogen oxides are converted into neutral gases, mainly nitrogen. In this way the NOx Trap is regenerated and is ready to go on trapping more NOx.

To ensure the NOx Trap operates smoothly, additional (oxygen and heat) sensors are positioned at the intake manifold and on the tailpipe. The data they capture is transmitted overthe controller area network to the ECU for managing the NOx Trap (deciding when to purge) and determining combustion modes (how to purge).


AdBlue is a solution made up of urea and water that’s injected into the car’s exhaust system before NOx leaves your exhaust. After it’s fed into the exhaust, it reacts with the NOx produced by the combustion process and breaks it down into harmless nitrogen and oxygen.

It’s a case of basic chemistry – at high temperatures, AdBlue turns into ammonia, and it’s this process that breaks down the NOx. And this significantly reduces the amount of NOx particles in exhaust emissions.

This process is managed by a Selective Catalytic Reduction (SCR) system. In a nutshell, AdBlue is injected through a catalyst in the exhaust.

Diagnosing SCR issues

Apart from running out of DEF (Diesel Exhaust fluid), there are many other issues that will cause a SCR equipped Renault to enter either a limited start, or a no-start mode. This is not to protect expensive components in the exhaust after treatment system but is purely to prevent excessive amounts of NOx from being released into the atmosphere when the SCR system does not work as intended.

DEF Depletion

DEF is stored in a dedicated tank, and during normal operation of a SCR equipped vehicle, the volume of a full tank of DEF is calculated to last the distance between scheduled services. However, sustained aggressive driving can deplete the supply of DEF at a higher rate. The DEF usage is usually about 1-4% of diesel, so for every 100L diesel used expect to use around 1-4 litres of DEF.

All Renault vehicles with SCR display a visual warning to the driver, which warning clearly indicates not only the level of the DEF tank, but also how many more times the vehicle can be started with the remaining DEF in the tank. If the DEF tank is run dry, the engine will enter a no-start mode immediately, and this mode will persist until the DEF tank is refilled and a system reset is carried out.

To do the reset procedure you need a scan tool with Renault specific software that can monitor and display Renault specific live data, as well as perform SCR resets.

You need to extract all active and pending fault codes but take note that the codes you find must NOT be cleared. If you clear any codes, the system will enter what is known as “Tamper Mode” and it’ll automatically enter a limited start cycle even if all repairs are carried out successfully.

Contaminated / expired DEF

All high-quality DEF consists of a mixture of 62.5% deionised water and 32.5% high-grade urea, which is the source of the ammonia that converts NOx into water and nitrogen. Every important aspect of SCR systems, such as the injection rate and storage capacity is designed around these percentages; in this proportion, the water and liquid urea freeze and thaw at exactly the same rate, which prevents one component in the mixture separating out of the mix in freezing temperatures.

While freezing temperatures are not an issue in Australia, majority of SCR systems now have a heating element in the tank to keep the DEF at a set temperature. All DEF mixtures sold in the world have the same relative concentrations of water and urea on the one hand and have a maximum shelf life of only 12 months. Most SCR catalyst faults are the direct result of issues in the DEF injection system. Blockages and leaks anywhere in the system (particularly leaking valves/injection nozzles) cause too much or too little DEF being injected and both conditions can cause issues with the catalyst filter itself requiring it to be cleaned which we can do at Exhaust Clean Australia utilising our patented industry leading machines. It is also recommended for the SCR catalyst convertor to be cleaned at regular service type intervals to maintain optimum efficiency.

Faulty NOx sensors

SCR systems use upstream and downstream NOx sensors to monitor the efficiency of the catalytic converter, and as with oxygen sensors, the ECU/SCR control module compares the output of both sensors to calculate the efficiency value for the SCR catalytic converter.

However, since NOx sensors are very expensive, all other possible causes must be investigated before any NOx sensor is deemed to be faulty.

Metering valve issues

Once you are certain that the DEF storage and injection systems are functional, you can use a suitable scan tool to perform a test of the metering valve. This test involves activating the injection pump remotely with the metering valve removed from the exhaust system. The valve should emit a very finely atomised spray pattern consisting of three clearly defined cones, and the amount of the DEF emitted during the test should weigh about 15 grams.

Diesel Oxidising Catalyst (DOC)

Your DOC is an integral part of the entire after treatment system in converting the nasty by products emitted by your Renault’s engine into safely breathable emissions that are no longer harmful to us or the environment. Regular cleaning intervals are recommended to ensure perfect operation of the DOC system to prevent costly failures, downtime without your vehicle and expensive repair bills. Exhaust Clean Australia, using our patented Italian made machines will keep your DOC operating like clockwork!!

Catalytic Convertors (CAT)

Catalytic convertors are an important part of the aftertreatment system on petrol powered Renault vehicles to reduce hydrocarbons, carbon monoxide and nitrogen oxides to drastically reduced levels that are safer for the environment. These by-products of the combustion process are fatal in an untreated state. CAT convertor health and condition is important to ensure your Renault is operating in a manner designed by the manufacturer to not cause harm to the environment as well as to us as human beings! Exhaust Clean Australia can clean your Renault’s CAT convertor restoring their efficiency to an ‘as new’ state drastically reducing the risk of costly repair bills, increased running costs and most importantly reducing the damage to environment!


The Intercooler on your Renault plays a vital role in your engine’s intake system. Cooling the incoming air temperature dramatically increases your vehicle’s performance, efficiency and contributes towards the reliability factor as well. Intercoolers are often overlooked maintenance wise till a problem appears or the vehicles performance has a noticeable drop in output. A dirty, oil filled intercooler will not be anywhere near as efficient cooling wise and if a turbo or other related engine failure has occurred the contaminants may well just be stuck in your intercooler ready to be digested back into the engine causing further possible damage. Exhaust Clean Australia’s revolutionary machines can return your intercooler to full efficiency and like new cleanliness giving you peace of mind trouble free motoring.

Exhaust Gas Recirculation (EGR)

The EGR system on Renault’s vehicles reduces the combustion temperature by diverting a small portion of the exhaust gases back into the intake manifold. The exhaust gases are no longer combustible so diluting the intake air with exhaust gases makes the air/fuel charge less combustible.

The engine management system opens or closes the EGR valve to control the flow within the EGR system. The EGR valve connects the exhaust manifold to the intake manifold. The EGR valve is normally closed and there is no EGR flow when the engine is cold, at idle, or during hard acceleration. The EGR flow is at its peak during steady cruising under moderate load. This has a quenching effect that lowers combustion temperatures and reduces the formation of NOx.

If the EGR system is rendered inoperative because it was disconnected or tampered with, the cooling effect that was formerly provided by the EGR system will be lost. Without EGR, the engine will often knock and ping (detonate) when accelerating or lugging the engine. This can cause engine damage over time.

The EGR cooler and valve over time on your Renault can become totally blocked with a build-up of carbon, oil and contaminants from the recirculating of the exhaust gases back into the intake system.

Common problems related to EGR system are as follows: -

  • Pinging (spark knock or detonation) because the EGR system isn’t working, the exhaust port is plugged up with excess carbon or the EGR valve has been disabled.
  • Rough idle or misfiring because the EGR valve is not closing and is leaking exhaust gases into the intake manifold.
  • Hard starting because the EGR valve isn’t closing and is creating a vacuum leak into the intake manifold.

Exhaust Clean Australia is equipped with industry leading technology to successfully clean and restore your EGR cooler and valve back to its original condition. Savings in fuel economy and the restoration for your Renault’s performance are the big benefits!! We also recommend having your mechanic perform an intake clean whilst we are taking care of your EGR system cleaning to receive the maximum benefits for your vehicle.

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