Fig. 1
CAN I FIX IT? Yes, I can!
Neil shows how the proper use of process can help with fixing a kind of fault not regularly seen
Fig. 2
Published: 05 August, 2020
By Neil Currie
Every now and then, you get a job that is unique. Once fixed, you never seem to get anything like it again. I recently had this with a vehicle and thought I would show how an unlikely fix was achieved, and the thought process behind it.
The vehicle was a Land Rover Discovery 3. As I have mentioned before, I work at a Land Rover specialist, so we see a lot. This one was recommended to us after another garage (which I seem to mention in most articles) had been unable to enact a repair. The customer’s complaint was that the battery had gone flat overnight after the interior lights had been left on. A friend had then jump-started the vehicle with jump leads. However, they had connected the jump leads with the wrong polarity onto the battery, and now the poorly Discovery wouldn’t start. It also had a dashboard lit up like a Christmas tree.
Method
Confirming the complaint, I sat in and cranked the vehicle and it spun over but did not fire into life. I then had a think about where to go next. From experience, when this happens fuses will normally blow to protect circuits. If the customer is lucky, it’s just a case of replacing the fuse, recharging the battery and off they go. I could either run through all the fuses in each fuse box, or I could connect a scan tool and carry out a global fault check to see if I could gain some direction. Perhaps an ECU wasn’t communicating and it was fuse fed, which would allow me to narrow it down to a certain fuse rather than checking them all. With these types of faults in my opinion there is no wrong way to approach it as long as its methodical.
Knowing this vehicle and its layout, I already knew that both fuse boxes, mainly the interior one, house a lot of fuses. As a result, I decided to go down the scan tool route to see if some diagnostic direction could be gained faster. Reading the engine control module showed a list of faults (fig.1; fig.2) but also indicated I had communication so the module was receiving power. The rest of the vehicle scan reported incorrect data from the engine ECU in most modules, which explained the other warning lights. When this model has information broadcast onto the can bus network which indicates there is faults within a module, it is normal to see multiple warning lights illuminate then clear when the faults have been rectified. Another observation I made was when the engine cranked, if the anti-theft system had been affected the vehicle would not crank whatsoever so hearing the starter turn also indicated that the security system was happy.
Knowledge versus information
This is where system knowledge is beneficial, but will not apply to all manufacturers, so technical information may be required to find this out. I then focused on the engine control module faults and why the engine would not start. Checking Topix (Land Rover’s information website portal) for fault code setting criteria, most of the fault code info suggested testing the wiring at the ECU, and if ok to suspect a faulty Engine ECU. So, I printed off the wiring diagram and made a test plan.
My plan was to check all powers and grounds at the control unit. Even though we could communicate and read fault codes and read live data, we still could be missing a power feed. Most control units have multiple power supplies both permanently and switched. The permanent feed is there mainly for what is known as KAM (keep alive memory). It can remember such things as the security link between the anti-theft system and other data, for example injector correction factors used for smooth running control and adaption memory for example the EGR valve. One reason a switched live is used is so that when the ignition is turned on, the module wakes up and is ready to work, and when the ignition is turned off can go to sleep and doesn’t drain the battery. There are other reasons for both which also can vary depending between petrol and diesel and manufacturers. Again, it’s important to have the correction information to hand to know the system operation.
Polarity
With my information to hand I gained access to the ECU, which on this model is located behind the battery. Testing each power and ground under load proved all to be good, so according to Topix we now needed a new control unit as the incorrect polarity jump start has damaged the control unit. At this stage I was in agreement, and decided to phone my local dealer and price a new unit up. Brand new, this control unit was at the time around £800 plus VAT, then required fitting and programming. I then took a step back and had a think about if anything else could be done.
I remembered many years ago reading an article by James Dillon, where he advised always thinking of what tests you would do if the part/repair did not fix the vehicle and doing them beforehand. With this in my head I then thought what else could I do? What if it was just a software issue and a possible update would rewrite over what may just be corrupt data? I myself had never seen it before and did not know the answer but for the sake of updating the software with the Land Rover factory scan tool I decided to give it a go. If it didn’t work then I was happy it needed a new ECU and I had learned something in the process.
The module did have an update available so I ran the procedure and then when complete I cranked the engine to see what happened. To my surprise the engine fired into life and all of my fault codes cleared except the 2 x EGR faults which after further testing were both faulty (a common issue on this particular engine). The vehicle was rebuilt and given a road test and all was well confirming the complaint was fixed. The customer was then notified and advised of the EGR issue.
Lessons
From this job, I learned that if there is possibly another test that can be carried out, do it and see if any more information can be gained. On this vehicle it was looking like a new ECU, so I had nothing to lose. It was just an idea I had, which I decided to do follow through on in the name of learning, due to my curiosity. Will this work every time? I highly doubt it, as in this case only the software was corrupted. If a large amount of current had made its way into the unit, then the small and fragile components would not have stood a chance which is what usually happens if they aren’t protected by a fuse. Luckily for the customer the repair only turned out to be a fraction of the cost of a new control unit and a lesson learned for his friend.
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- technologies of electric and hybrid vehicles
In the previous two issues, we looked at the way batteries store energy. We could in fact compare a battery to a conventional fuel tank because the battery and the tank both store energy; but one big difference between a fuel tank and a battery is the process of storing the energy. Petrol and diesel fuel are pumped into the tank in liquid/chemical form and then stored in the same form. Meanwhile, a battery is charged using electrical energy that then has to be converted (within the battery) into a chemical form so that the energy can be stored.
One of the big problems for many potential owners of pure electric vehicles is the relatively slow process of
re-charging the batteries compared to the short time that it takes to re-fill a petrol or diesel fuel tank. If the battery is getting low on energy, the driver then has to find somewhere to re-charge the batteries, and this leads to what is now being termed ‘range anxiety’ for drivers.
Whilst some vehicle owners might only travel short distances and then have the facility to re-charge batteries at home, not all drivers have convenient driveways and charging facilities. Therefore, batteries will have to be re-charged at remote charging points such as at fuel stations or motorway services; and this is especially true on longer journeys. The obvious solution is a hybrid vehicle where a petrol or diesel engine drives a generator to charge the batteries and power the electric motor, and for most hybrids the engine can also directly propel the vehicle. However, much of the driving will then still rely on using the internal combustion engine that uses fossil fuels and produces unwanted emissions. The pure electric vehicle therefore remains one long term solution for significantly reducing the use of fossil fuels and unwanted emission, but this then requires achieving more acceptable battery re-charging times.
Charging process and fast charging
Compared with just a few years ago, charging times have reduced considerably, but there are still some situations where fully re-charging a completely discharged electric vehicle battery pack can in take as long as 20 hours. It is still not uncommon for re-charging using home based chargers or some remote chargers to take up to 10 hours or more.
Although there are a few problems that slow down charging times, one critical problem is the heat that is created during charging, which is a problem more associated with the lithium type batteries used in nearly all modern pure electric vehicles (as well as in laptops, mobile phones and some modern aircraft). If too much electricity (too much current) is fed into the batteries too quickly during charging, it can cause the battery cells to overheat and even start fires. Although cooling systems (often liquid cooling systems) are used to help prevent overheating, it is essential to carefully control the charging current (or charging rate) using sophisticated charging control systems that form part of the vehicle’s ‘power electronics systems.’
Importantly, the overheating problem does in fact become more critical as battery gets closer to being fully charged, so it is in fact possible to provide a relatively high current-fast charge in the earlier stages of charging; but this fast charging must then be slowed down quite considerably when the battery charge reaches around 70% or 80% of full charge. You will therefore see charging times quoted by vehicle manufacturers that typically indicate the time to charge to 80% rather than the time to fully charge. In fact, with careful charging control, many modern battery packs can achieve an 80% charge within 30 minutes or less; but to charge the remaining 20% can then take another 30 minutes or even longer.
Battery modules
Many EV battery packs are constructed using a number of individual batteries that are referred to as battery modules because they actually contain their own individual electronic control systems. Each battery module can then typically contain in the region of four to 12 individual cells. One example is the first generation Nissan Leaf battery pack that contained 48 battery modules that each contained four cells, thus totalling 192 cells; although at the other extreme, the Tesla Model S used a different arrangement where more the 7,000 individual small cells (roughly the size of AA batteries) where used to form a complete battery pack.
The charging control systems can use what is effectively a master controller to provide overall charging control. In many cases the electronics contained in each battery module then provides additional localised control. The localised control systems can make use of temperature sensors that monitor the temperature of the cells contained in each battery module. This then allows the localised controller to restrict the charging rate to the individual cells to prevent overheating. Additionally, the localised controller can also regulate the charging so that the voltages of all the cells in a battery module are the same or balanced.
One other problem that affect battery charging times is the fact that a battery supplies and has to be charged with direct current (DC) whereas most charging stations (such as home based chargers and many of the remote charging stations) provide an alternating current (AC). Therefore the vehicle’s power electronics system contains a AC to DC converter that handles all of the charging current. However, passing high currents through the AC to DC converter also creates a lot of heat, and therefore liquid cooling systems are again used to reduce temperatures of the power electronics. Even with efficient cooling systems, rapid charging using very high charging currents would require more costly AC to DC converters; therefore, the on-board AC to DC converter can in fact be the limiting factor in how quickly a battery pack can be re-charged. Some models of electric vehicle are actually offered with options of charging control systems: a standard charging control system which provides relatively slow charging or an alternative higher cost system that can handle higher currents and provide more rapid charging.
Home & Away
One factor to consider with home based chargers is that a low cost charger could connect directly to the household 13-amp circuit, which would provide relatively slow charging of maybe 10 hours for a battery pack. However, higher power chargers are also available that connect to the 30-amp household circuits (in the same way as some cookers and some other appliances); and assuming that the vehicle’s AC to DC converter will allow higher currents, then the charging time could be reduced to maybe 4 hours operate (but note that all the quoted times will vary with different chargers and different vehicles).
Finally, there are high powered chargers (often referred to as super-chargers) that are usually located at motorway services or other locations. These super-chargers all provide much higher charging currents to provide fast-charging (as long as the vehicle electronics and battery pack accept the high currents); but in a lot of cases, these super-chargers contain their own AC to DC converter, which allows direct current to be supplied to the vehicle charging port. In effect, the vehicle’s on-board AC to DC charger is by-passed during charging thus eliminating the overheating problem and the high current DC is then fed directly to the battery via the charging control system.
In reality, the potential for re-charging a battery pack to 80% of its full charge in 30 minutes or less usually relies on using one of the super-chargers, but battery technology and charging systems are improving constantly, so we
will without doubt see improving charges times for
newer vehicles.
