Signs your SCR system isn’t working at its best

In 2017, the number of AdBlue breakdowns the AA dealt with hit around 23,000. AdBlue-related breakdowns are all too common and expensive to fix, which is why it’s important to spot the signs of a failing SCR system as soon as possible. You want to minimise the damage. So how do you know if your AdBlue system isn’t operating as it should?

When it isn’t working properly, there are a few signs which can show there’s a problem. So here are some problems to look out for.

Lack of power

We call this state ‘limp mode’ and it’s a security function of your engine and transmission. When the engine recognises there’s a fault, the machine enters limp mode which reduces power and limits the engine’s RPM to prevent damage.

If your machine suddenly becomes slow and stops revving past a certain point – and if the engine light is showing – it’s in limp mode. Turbo boost may shut off and, if it’s an automatic, transmission might seem stuck in one gear. If your vehicle or machine enters limp mode, you need to get it fixed as soon as possible. 

Limp mode can occur if your engine runs out of AdBlue. Refilling the Adblue system can sometimes solve the problem, but limp mode can also result from AdBlue contamination which may require professional servicing. 

Smoke

If you see black smoke coming out of your exhaust, the problem might not be with the SCR system, but with the attached diesel particulate filter (DPF). The filter traps soot from the burning of diesel. It then gets rid of this by burning it when the engine is working at a high intensity. However, if the engine consistently operates at low intensities, the soot builds up and causes blockages as well as dirty black smoke coming out of the engine. 

To fix this problem you may need to use your engine at a higher intensity for a while to kick-start the regeneration process. However, if the blockage is severe, you may need to replace the filter which can be expensive. DPF replacement and installation can cost up to £2,000. A cleaning can cost around £135 and maintenance £100. Because your DPF can be so pricey when things go wrong, it’s good to stay on top of things and prevent buildups by starting the regeneration process regularly.

Warning lights

You should pay attention to your warning lights so you can stop any SCR system problems from developing. There are three lights to look out for:

• AdBlue low-level yellow – This is a warning that your AdBlue levels are low. It should come on a long time before your tank is completely empty. If this light comes on, fill the AdBlue tank.

• AdBlue no-restart red – If you ignore the low-level warning, your Adblue tank can run dry and in some cars, once this light comes on, you cannot restart your engine once you turn it off. This is to prevent people driving without AdBlue, so if this light comes on, fill the tank immediately. 

• Service engine – This light may come on if there’s a technical problem with your SCR system. It could mean an issue with the delivery system, the fluid level sensor, or with incorrect fluid. If you want to solve the problem, you’ll need a diagnostic scan tool to read the error code. But if you ignore this light, you could end up permanently damaging your SCR system.

There’s a lot to think about when using a fleet which relies on AdBlue. You should always carry out a cost-benefit analysis to see how the cost of frequent and likely SCR system breakdowns will eat into your profit margin. If you find the cost is high, there are ways you can avoid these problems and save money.

DPF Doctor can provide your fleet with a simple kit that overrides the need for AdBlue and DPF systems in your fleet. It’s a quick, legal fix to the high costs of running modern diesel engines. One small investment can save you thousands so get in touch with us today.