|Vehicle details:||Komatsu PC210 LC|
It’s becoming somewhat of a running joke here at Pico that Steve gets to go and play with some of the finer machinery VM’s have to offer and I find myself ankle deep in a field, complete with thermals, looking at something that has been run till it stopped. Personally, I love the challenge these machines bring, as your approach to diagnosis has to change. Parts aren’t available off the shelf, can’t normally be ordered the same day and are, on the whole, 3-4 times more expensive.
The following adventure started with a back story where the machine had been looked at previously and parts had been replaced. I had a quick chat with the operator who reported that after the second time it was looked at it worked for around four hours before moving to a level 4 warning where the engine was derated and performance from the machine was seriously downgraded to the point where only a high idle engine speed was possible. The other rather annoying part of a level 4 warning is a constant sounding alarm as soon as the ignition was switched on, with no way of turning it off till the fault was fixed.
The interesting part of this story was that this machine had suffered similar problems previously and that the AdBlue/DEF injector had been replaced twice. I have been told that a genuine DEF injector cost around £600 which meant we were already into £1200 worth of parts and the machine was still not workable.
As with all diagnostic jobs, verifying the fault was one of the first tasks. As I expected, when I switched the ignition ON, we heard the level 4 warning alarm and the display showed the current abnormality. The fault codes can be looked up in the technical manual but the level 4 warning, AS00R4, was indicating that the fault for the level 1 code, CA3568, still existed after a repair and following a predetermined length of time. This length of time depended on the specification for the machine.
Whenever we are dealing with AdBlue issues I always make sure there is additive in the tank as well as check the AdBlue quality. AdBlue or DEF, Diesel Exhaust Fluid, is made up of 32.5% solution of urea 67.5% water and freezes below -11C. If a machine is running low the warning light will illuminate and if is not topped up it will eventually derate the engine. If it runs out completely, it can prevent the machine from starting. In this instance, there was so much AdBlue present that it was coming out of the breather. A built-in sensor reported that the concentration level was 33.2%. If you can’t read a quality sensor there are refractometers available to test the quality.
We could not see any obvious issues from the visual inspection so our attention had to be with the level 1 code CA3568, which is for AdBlue/DEF injector malfunction. First up was to check the injector activity with PicoScope to see if the machine was making an electrical attempt to drive the injector.
Channel A – Supply
Channel B – Ground
Channel C – Current
Komatsu is well known for having one of the most comprehensive monitors. In a way, it can function as a scan tool where you can bring up live data, clear codes and also perform active tests. As the fault was still active, the injector was not activated during a normal run of the machine. To obtain the capture above, we ran an active test for the injector through the monitor. This is a pulsing action that explains the consistent timing of the injector events. If you want to see the very fault codes on a demo of the Komatsu monitor, please click here.
We were happy that the injector could be controlled and we could even make out the pintle hump that indicated that the injector was moving.
Determining why the injector was not activated during normal running was next on the list. One thought was that if the ECU was seeing an incorrect sensor value, it may not command the injector as there couldn’t possibly be another injector there.
When we took another look at the monitor, we observed the NOx sensor output values.
We knew that the AdBlue wasn’t being injected, which explained the high level of NOx at the SCR outlet, but the turbo outlet concentration level would sit static and not change even slightly. It was as if it were stuck, but when we increased the load on the engine by raising the boom, we saw the readings drop into the negative values before they proceeded to jump around till the engine was left idling and then the values returned to the static value. Figuring we could still be relatively non-intrusive as the NOx sensors were visible and very accessible, we connected the scope to the CAN H and CAN L terminals of the SCR outlet NOx sensor.
By capturing the data with PicoScope, we could apply the J1939 serial decoder to help us see the header in the correct format. This helped us to distinguish between the various ECUs present on the Aftertreatment network. In this machine’s case, the Aftertreatment ECU was actually built into the Engine ECM which was why we had the NOx sensors and the engine on the same network. I applied a link file that shows the PGNs and source address values in a readable form. I’ve highlighted the Aftertreatment gas 1 which I assumed would be the NOx sensor at the turbo outlet/exhaust inlet. The data suggested that nothing was happening, yet our monitor was showing a value of 240 ppm. I exported the data into CSV to better manipulate it to view the values using the J1939 DA document.
There is more information on the forum regarding how to determine values from data captured with PicoScope and the information available in the J1939 DA document. You can find out more from one of our users and later in the post I explain how to export and view the data in the above format.
I’ve also added the data from the outlet NOx sensor where it hovered just over the 140-ppm value. This tied up with the data on the monitor. Could it be that we have a faulty NOx sensor? I could not rule it out but it was time to get a little more intrusive. We decided to remove the injector and see if we could use the active test to fire the injector to see if we had a blockage.
The second record on the list was for AdBlue/DEF injector overheat caution at 6347 hours, just 20 hours before we visited the machine. Below this, were two records relating to the engine cooling system, one being the engine water overheating. This isn’t that uncommon in construction equipment. The environments these machines find themselves in are usually extremely dusty and pulling in air to cool the engine will drag this dirt and dust in and clog up the radiator. Could these records be linked to the injector failures?
Removing the cooling pipes for the injector body told us everything we needed to know. As you can see from the image above, the port was completely blocked. Removing the pipe outlets from the body allowed us to see further in and, sure enough, the whole thing was completely blocked and not allowing any coolant through around the injector.
I hadn’t quite realised how important cooling was for AdBlue injectors. Where I was first subjected to AdBlue in the automotive world, the injectors usually have large heat sinks attached to them and would be placed where air could travel over the injector as the vehicle was in motion. As the injector would only be subjected to high temperatures during regeneration, this would only happen while the vehicle was being driven. With this type of machinery, however, airflow isn’t possible so cooling has to be done by other means. With yet another injector on order, and the pipework and coolant pathways to the injector body cleaned out, we hope we found the cause of the issue. The recommendation, though, is to give the cooling system a thorough flush before it is being put back to work.
More and more exhaust Aftertreatment systems are found on all types of off-highway machinery and this brings about more complications. We wondered if there was a test we could carry out to quickly check the operation and health of the main actuating components. The system fitted to this Komatsu is the Bosch Denoxtronic 2.2. It can also be found on some light and medium commercial vehicles. You can see a very basic layout of these actuator components in the illustration below.
To come up with a test that can be carried out even in the event that you cannot manually run an active test on the pump and injector, we first needed to understand how the system works.
Fundamentally, there are always a set number of components for an AdBlue Aftertreatment system. These consist of:
The actuating part of the circuit is easier to explain with a hydraulic diagram:
When the ignition is switched on, the pump will prime the system once the fluid is up to temperature. The pump will draw fluid from the tank where the pressure will begin to rise to around 9 Bar (130 psi). This pressure is created by the throttle in the return line to the reservoir, pressure is the resistance to flow. A one-way valve prevents the fluid from entering the supply lines from the reservoir on the return side.
During operation the injector will be commanded to open by the Aftertreatment ECU, allowing the solution to enter the exhaust system to begin the chemical reaction. When AdBlue is introduced to a high-temperature environment the urea breaks down to form ammonia and Isocyanic acid. This combines with the water vapour in the process of hydrolysis and creates CO2 and NH3 (ammonia). In an environment containing a catalyst and high levels of oxygen, found in lean-burn engines following combustion, the ammonia will combine with NOx present in the exhaust gas to form nitrogen, carbon dioxide and water.
When the engine is switched off, the Aftertreatment ECU will command the 4/2 flow control valve (6.), shifting its position so that the pump is now pulling the fluid from the supply line and returning it to the reservoir. Due to the one-way valve and the closed position of the injector, a vacuum will start to build in the pipework. To prevent the collapse of the pipework, the injector is pulsed at a high frequency to allow air into the pipework and control the amount of vacuum present. The pressure sensor will detect vacuum changes in the pipework, which can be useful when you are looking for blockages.
With a better understanding of the system, we did a quick test by running the active test while monitoring the pressure sensor, pump current and DEF injector.
Channel A – AdBlue pressure
Channel B – AdBlue pump current
Channel C – AdBlue/DEF injector
Look at Channel A. The pressure before the test started was reading 791 mV which would indicate atmospheric pressure as the system had not been run. As the pump started, we can see the current change showing that work was being done and that the pressure began to rise. Once the pressure had stabilized, the injector was activated. When the test stopped, the pressure immediately dropped as the 4/2 valve was opened. With the pump still turning to bring the AdBlue back to the tank, we started to see the vacuum begin as the pressure dropped below the atmospheric ruler and continued to fall to a voltage of 609 mV. The injector was activated but there was no change in the pressure reading which could indicate that there was a blockage.
In contrast, below is a capture done on a known good system (although the connections were slightly different). Pressure remained on Channel A but we used voltage for the motor speed rather than the current on the supply.
When we measured the pressure voltage during the purging of the system, we can see that it didn’t go below 800 mV. This led us to believe that we were seeing a blockage through the pressure sensor on the faulty machine.
With the new injector installed, we cleared the codes and took another capture while the system was operating.
It was really interesting to see that while the injector current was flowing we could see a drop in the AdBlue pressure. This indicated that the AdBlue was indeed being delivered into the exhaust system. As this is a known good, we can use this drop in pressure to help highlight issues with blockages in the future. If there were problems with NOx levels despite this pressure drop, we would have to turn our attention to the spray pattern or the actual SCR catalyst.
When we looked at the purging side, we could now see that the pressure voltage sat steady at 770 mv, which I was happy with.
I hope this helps in some way. There was a slight detour during the diagnosis but having better product knowledge may have moved the action plan away from the possible CAN testing. However, it is safe to say we learned something new! My thanks to Roy at RCT Power Services for the opportunity to join him on this diagnostic adventure.