Let’s Amarok!

Additive delivery to diesel engines can be a headache, and Frank found himself dealing with just such an issue recently

By Frank Massey |

Published:  25 July, 2022

This month’s topic looks at a VW Amarok 3.0, engine code DDXC, with SCR additive emission control.

It is the additive system we will focus on, no surprises there. Presented to our workshop with the coil lamp illuminated, displaying no loss of performance or fuel economy. The owner is a neighbour of my son David who conducted all the following diagnosis and collation of test data. The owner purchased a £20.00 eBay special code reader extracting the simple message “NOx sensor.” It is my intention to focus on the diagnostic process as well as the repair decisions are undertaken.
Most mistakes are often made before any work begins. So, the initial triage is vital in understanding the customer’s requirements, as well as your actions, therefore cost.

With that in mind out comes the ODIS diagnostic platform, vital in this evaluation, as will become apparent later. Please refer to the serial fault data as seen in Fig.1 and Fig.2. The important point to make here is the additional volume of data and specific component identification, this helps to correctly locate the item on the vehicle. There will be an additional advantage in driving the vehicle, observing specific data for the NOx additive system, I.E pre-repair data. This can later be compared with post-repair data. I will cover this later when we consider pre/post-Datazap images. As technicians, we must be conversant with the systems we intend to interrogate. This should include a system functional overview and component location, including manufacturer’s TSBs.

The test drive confirmed post-catalyst NOx levels higher than pre-NOx catalyst levels. It also confirmed an over-aggressive NOx additive injector function. Other critical observations related to exhaust gas temperatures, and catalyst efficiency. Low exhaust gas temperatures on load may suggest EGR faults. Do not reinvent the wheel; If there is a known fix identified by the VMs then include it in your repair. So, David conducted a TSB campaign search.
The search initially did not show any known campaigns for the fault code P103300 (237) G295 NOx sensor.  However, it did list a very interesting known issue with NOx sensor calibration?
Please refer to Fig.3, an image from ELSA. As this was unknown to David, he carefully read the process and required tools. ELSA identified an issue with NOx control module, and incorrect calibration. This requires the VAS 601 011 flash box. Whilst waiting for the shiny new toy to arrive at £400.00 the next often overlooked action is testing the urea additive quality and injector delivery rate.
There are only two tools required for urea quality, a refractometer, and your nose. If it smells like a urinal it’s knackered. It should be odourless. The ammonia must be 32.5%, as an exercise check your deliveries and all brands for compliance. You will be shocked at the results. We find the VM brands most reliable.

In the next test, ODIS is mandatory. It involves selecting the exact vehicle I.D, attaching a measuring beaker, removing the additive injector, then conducting a timed discharge test. There will be a very specific value, which must correct.
Please refer to Fig.4, which shows the VAS 601 011 tester. Using this calibration tool is very simple. Like most dealer tools, it doesn’t require any technical ability to use and is void of any data when in use. The NOx sensor lead is removed from the vehicle loom and connected to the flash box. Push the button and await the green tick to appear. During a discussion at Autoinform Dublin, it was suggested the tool does not evaluate or test the sensor, merely updates the control module firmware.
This sounds suspiciously like it was not done at the factory or the goalposts have been moved to avoid the MIL light errors. With all the above tests correctly, passed David was then able to re-check the vehicle additive system.
With performance not affected, David was keen to establish if the urea consumption was excessive. This was confirmed as one tank urea per two of fuel. We know the injector is delivering the correct volume, so there must be another reason.
Returning to the efficiency data, and injector delivery ratio he noted the following. Please refer to Fig,5 and Fig.6, which show SCR CAT efficiency. The NOx catalyst efficiency was well down at .354/.495 when 1.000 is correct, so the focus shifted to the catalyst efficiency. The vehicle has only done around 54,000 miles so we were not expecting a problem. Removing the exhaust system from the front and rear allowed inspection with our ender scope.

So here is the rub; Look at the pre-repair and post-repair Datazap images as seen in Fig.7and Fig.8

  •     Fig.7 shows yellow trace, SCR injector activity, excessive during normal smooth driving.
  •     Fig.8 white trace, NOx sensor 1 G295 upstream, high concentration NOx, 580ppm.
  •     Fig.8 blue trace, NOx sensor two, G687 downstream even higher concentration of NOx, 707ppm.

Back to the specific DTC David extracted at the beginning of the exercise; NOx sensor G295 signal low? It is not low – it is just lower than sensor 2 G687, which is very high. The problem is now obviously a dead NOx catalyst. Further close examination of ECTA shows several updated catalysts for this vehicle application, so the manufacturers have previous experience of premature failure. What? No recall programme? Don’t be silly. The active coatings which reduce NOx, platinum, palladium, and especially, barium have obviously been insufficient in earlier substrate manufacture. Why are NOx higher coming out of the catalyst? Quite simple really; The rear sensor is reporting the incoming NOx plus the stored NOx in the dead catalyst.

New catalyst
Now let us look at the new catalyst. Please refer to Fig.9 and Fig.10.
Fig.9, SCR injector activity normal, occasional intervention. Fig.,10 white trace NOx sensor 1 G295 normal NOx activity. Fig.10, blue trace NOx sensor 2 G687, passive activity confirming no NOx emissions.
Straightforward? It can be, providing you follow the correct process with the correct information and tools, not forgoing the £2,000 for the catalyst plus our costs.

This is why I love cycling!

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