Learn the skill of reading and interpreting vehicle electronics.
One of the most frequent comments we hear from CM readers is that modern cars have become so reliant on electronics that it’s becoming virtually impossible for home mechanics to work on them without spending a small fortune on diagnostics equipment. However, a suitable diagnostics device needn’t cost the earth and a basic ability to read – and, more importantly, interpret – fault codes can be learned by anyone. It’s a skill that’s essential for every 21st century motorist to understand how their car is performing, as well as what is going wrong.
Thinking outside the box
While much of this feature focuses on diagnostic equipment, a good home mechanic must never make the mistake of thinking that identifying faults and making repairs to modern vehicles can be performed solely using an offthe-shelf diagnostic device. Even the professional motor trade is struggling to change public perception about the process of automotive problem-solving, because many of their clients believe that a quick (and, they assume, cheap) plug-in cure is all that is necessary to resolve a fault, including extinguishing a troublesome engine management warning lamp, and this is all that stands between them and an MOT pass.
Diagnostics is a complex problemsolving process that entails investment in not only hardware and software, but also training and experience. With increasing numbers of people turning to both garages and DIY diagnostic equipment suppliers in the hope that ‘the box’ alone will solve their problem, it can be argued that they are caught in a distress purchase loop. Try to keep a level head and do not allow your judgement to be clouded by the pressing need to get back on the road as quickly as you can.
Throughout his many years of training professional mechanics, Neil Hilton of Hella Gutmann Solutions told us that the single biggest mistake he encounters is an over-reliance on fault codes. This might be because it is human nature to take the easiest option. Diagnostics cannot be about a machine alone, because human thought processes are integral to the problem-solving process, which includes evaluating critically the information that is presented (including that from a diagnostics machine – this includes fault codes) and coming to a logical conclusion. This is where skill and experience remain as relevant as ever and is how professional workshops justify their charges. It is no coincidence that ‘diagnosis’ is derived from the Greek word meaning ‘knowing thoroughly’ – you have to evaluate the symptoms to arrive at a logical root cause of the problem, gathering information from different sources and use your eyes and ears to sense if anything is unusual, rather than simply taking fault codes as gospel.
Interpreting & dealing with fault codes
Unlike a traditional oil pressure warning light that relies on a fairly simple electrical circuit to indicate one specific fault, other fascia warning lamps can relate to a number of issues that have been logged by an ECU. Notably, these include the engine management
warning lamp (known otherwise as a malfunction indicator light or MIL), Abs/traction control and SRS (airbags). As the faults cannot be pinpointed to a single issue, the relevant computer needs to be interrogated for a fault code, which could help to narrow the problem to a particular component in a circuit, such as a sensor. It may be worth trying to reset the code before investigating further. Should the reset fail, or the same fault code reappear after a short time, then it is unlikely that the fault generated is a ‘ghost’ code, which may have been triggered by something else, such as electromagnetic interference, or a sudden dip in voltage, which might have been caused by an ailing battery.
While the ECU obtains data from a number of information sources, not all of them are accurate. For example, the engine ECU might identify a Lambda sensor as faulty, due to excessive exhaust emissions not being reduced successfully by adjusting the fuelling, when the real cause is a leaky fuel injector, the solenoid of which is returning signals to the ECU that are within tolerance.
Bear in mind that even modern engines do not have sensors that monitor crankshaft, flywheel or piston conditions. Further limiting factors include universal fault codes being restricted in number, as well as a need to consider that the code itself might not indicate a problem with a component, but rather the circuit that the ECU associates with it – the wiring, connector plugs and even other associated components upstream could be to blame for sending false signals.
This includes bad earths, which can trigger a plethora of codes. Check the basics, such as inspecting earth leads for corrosion and evaluating the battery and alternator performance, before replacing components blindly.
Thijs Jasink of Actronics, a company that remanufactures electronic components, told CM that 30-35% of the parts that it receives have nothing wrong with them, especially ECUS. Most commonly, the mechanic has misdiagnosed the component as being the fault. However, specialists such as Actronics, are worth contacting for advice, because they can either interrogate the ECU in more depth for you, or else offer advice about any other component that may be influencing the ECU in a certain way.
Consider also that fault codes can be temporary, indicating the presence of an intermittent problem. In certain cases, should the relevant ECU detect that the anomaly is not present any longer, it may extinguish the warning light but the fault code may still be logged in the system. If the lamp, especially the MIL, has been lit for a fairly long period of time, several components may be responsible. Addressing one fault may not present a solution, because you have freed-up a longer list of multi-layered problems that the original issue may have masked. This is why it’s essential to address any warning lamp as soon as possible.
When servicing the vehicle yourself, you may uncover a list of fault codes that are not serious enough to warrant illuminating a fascia-mounted warning lamp. These can range from codes involving the body control computer to the climate control system. Should you suspect that they have been present for a long time, some diagnostic devices will permit you to check not only if they are permanent, or intermittent, but also the frequency wth which they appear.
Programming & coding
In the past, you could reset an engine management, ABS, or even SRS ECU by disconnecting the battery for several minutes. Modern vehicles are more sophisticated. Many models have specific battery disconnection/ reconnection procedures that must be followed to avoid damaging their delicate electronics. When a major repair has
been completed, recalibration of certain engine functions might be required. For example, direct-injection petrol engines can suffer from their intake tracts becoming clogged with rubbery carbon that restricts airflow. Being a gradual process, the ECU relearns and adapts accordingly without illuminating the MIL, or logging a fault code, provided that the conditions remain within tolerance. However, when the inlet is cleaned, the sudden difference might confuse the ECU, hence why either resetting or recalibration is necessary.
While diagnostic tools are needed to code certain new/remanufactured replacement parts to your car, such as ECUS and fuel injectors, the tool might be needed for certain service procedures. On some Mercedes-benz models, for example, the simple DIY task of replacing the air filter dictates that the ECU needs recalibrating to take into account the sudden change in airflow characteristics. Not resetting either the service/oil quality intervals diagnostically can make many models assume that a service has not taken place. This can reduce active diesel particulate filter regeneration rates, for example, and increase the risk of either filter, or turbocharger damage.
Additionally, replacing the smaller and lighter batteries on many modern cars that possess smart charging systems requires the new battery to be registered and programmed to the car, which resets the charging algorithms within the monitoring software to ensure that the fresh battery is charged adequately. The diagnostics procedure should remove any low battery warnings as well. Failure to do this will affect the operation of other systems, such as the stop-start function.
Which diagnostic tool to choose
No clear definition exists between an aftermarket code reader, a scanner, or a diagnostic tool, so take marketing claims with a pinch of salt when considering the huge range of devices available.
Inexpensive fault code readers have been around for many years and can access generic fault codes within the engine management ECU. However, the least expensive types may not be able to provide you with manufacturer specific codes, let alone provide any further diagnostic information. The very cheapest tools will not necessarily be able to access the ECU for every make of car, provide you with live data readings, or perform actuation tests and programming functions. You should also ensure that the equipment can save or print any live data readings, so that you can compare them. If your budget will stretch to it, investing in equipment that will provide additional data, such as wiring information, will give you a better chance of pinpointing and identifying the fault, without replacing parts that are in good order.
Consider your needs, too. Your choice of device will depend on whether dedicated diagnostics are needed for just one car, or whether you look after a number of different vehicles in your household and/or like to change your car regularly. You can buy ‘cracked’ versions of the car-maker’s own software from various sources for a one-off fee, but these tend to work only if you favour a certain make. While you should be able to conduct most of the services supplied by main dealer diagnostic devices, programming/coding may be limited, as are certain updates, because your ‘pirated’ software might not be able to access the maker’s server.
A number of diagnostic device suppliers are specialising in certain makes to provide more in-depth functions. Carly, for example, has both free and professional (costing £43.99)
apps for each of the major German manufacturers and for Renault, which is used via a VCI (costing £44.90) that sends the information via Bluetooth from the EOBD socket to your mobile phone, or laptop. It can read and compare mileages between ECUS and alerts you of any discrepancy that might indicate odometer fraud. Make-specific diagnostics can also permit you to make advanced adjustments, such as cruise control tolerances (which can have a positive effect on fuel consumption), and change interior lighting/warning noise characteristics.
Investigate if any subscription/update fees are charged, too. The Nebula Mech 5, for example, covers multiple models but, aside from the £150 cost for the VCI, it operates via a cloud-based system that requires a £29 annual subscription fee (of which the first month is free) to access updates. However, you pay only when you use it and the retailer that we contacted, Hickleys, told us that it works to the same level as a professional tool costing between £2000-£3000 and will conduct fuel injector coding as well.
Generic hand-held code readers are offered by several respected tool companies, but their outright purchase prices can be quite high, although you can balance this against the features, make/models covered, as well as the cost and availability of updates.
Should you own a car from a Japanese, Chinese or Korean manufacturer, note that some generic systems might not offer the best support for those models and the vendor should be questioned carefully. Decide on your preferred interface – would you prefer laptop/tablet/mobile, for example – and do you need your VCI to be Bluetooth-compatible?
Unless you can be sure that the buyer is reputable and preferably Uk/europebased, we do not recommend buying diagnostic equipment through online marketplaces such as ebay or Gumtree. The lure of a bargain might tempt you, but the level of technical support must be questioned, as well as the availability of updates and the risks associated with plugging a VCI of unknown origin into a relatively expensive vehicle.
Advanced diagnostics – ADAS calibration
Diagnostic basics were covered in depth in the June 2017 issue of CM. However, the increasing (and often mandatory) use of Advanced Driver Assistance Systems (ADAS), especially in the last five years, means that more in-depth diagnostic calibration is becoming an increasingly relevant post-repair safety issue.
From a DIY perspective, the situation is worth considering, because many early Adas-equipped cars have entered the secondhand market and may no longer be under warranty. The latest ADAS safety functions, which include road sign recognition, auto-parking, adaptive LED matrix lighting and pedestrian detection, rely on sensors, cameras and long- and medium-range radars that are positioned within the structure of the doors, behind the front grille and on the bumper corners, not just within the windscreen. Many of these require individual calibration. For the latest models, post-repair calibration will add to repair costs significantly, until such a time arrives when self-correcting systems are developed. For now, however, many older Adas-equipped cars feature a windscreen-mounted camera, which is why the calibration of this system alone is our focus.
Front screen-mounted sensors have been around for more than a decade, offering auto-lighting and windscreen wiper activation. These are being replaced by cameras and long-range lasers that offer safety functions to influence the brakes, engine and even the steering. Should they not be calibrated correctly, the car may not react safely to a potential hazard. For example, a misalignment of a windscreen camera by one degree can cause an inaccuracy of up to seven metres.
Hella Gutmann Solutions has been providing ADAS maintenance and calibration services outside the main dealer networks for five years. Its head of business development Neil Hilton told
Car Mechanics: “Incapable diagnostic tools, lack of knowledge, expertise and training, tied with unsuitable processes, are proving to be real headaches with maintaining the calibration of these critical safety systems.”
It is not always straightforward to know which, or how many, of these systems is installed in a particular vehicle. Just as various older car models used to have to share the same wiring looms between the basic and top-of-therange versions, certain modern cars are being equipped with the same hardware but some trim variants might lack the software to run them. Should you be able to see either a sensor, or front-mounted camera, through a small cavity in the top centre of the windscreen, do not presume that it is operational. Should it be programmed, the single camera might control several separate functions. The only way that you can verify a particular model’s specifications is to perform a global scan on your diagnostic tool and note which ECUS are communicating.
The main issue surrounding ADAS technologies for a DIYER is that they can stop working, or not operate correctly following a home repair. While a nonfunctioning ADAS system does not currently mean an MOT failure (unlike the MIL, for example), an insurance company might refute a claim if it is found that a faulty driver assistance system was a contributory factor in an accident.
The majority of Adas-equipped cars, made in the last seven years, need recalibration after any work has been carried out that affects the suspension geometry. Typical MOT failure repairs that tend to be within a Diyer’s remit – such as replacing a balljoint, suspension arm or springs and dampers – will require a diagnostic camera calibration afterwards. While many cars that were registered within the last five years incorporate at least two ADAS systems, diagnostic calibration will become even more relevant to the DIY repairer as these vehicles become older and newer ones become more sophisticated.
Unfortunately, while you might be able to read the fault codes, no DIY diagnostic equipment is available to calibrate these systems. Hella Guttmann Solutions is one company that has developed its diagnostic systems for aftermarket garages, meaning that you are not obliged to visit main dealers. The equipment combines traditional but high-end diagnostic equipment with camera and sensor calibration (CSC) hardware, using vehiclespecific calibration boards. Therefore, if you are replacing components on a modern vehicle (either doing the work yourself or through an independent workshop), having the cameras calibrated afterwards is the only way that you can complete the repair safely.
The procedure has similarities to a human eye test and is demonstrated below. It highlights not only the latest in diagnostic interrogation and calibration, but also the importance of global scanning and how interrogating one system might influence another separate component. While not a DIY task, we would advise strongly that you ask the workshop to provide a calibration certificate that you can file with your car’s service history.
Automotive diagnostics is much more complicated than plugging in a fault code reader. Decent tools will give you additional information that will allow you to make a more accurate diagnosis.
Should you suspect that a sensor is faulty, you can back probe and measure its values with a multimeter. In many cases, you will need the values from which you can compare the result. Advanced diagnostic hardware can provide this information.
On newer cars, the specification is not always obvious unless a global diagnostic scan is performed. This distance radar sensor fitted to a four-year-old VW Passat is hidden from view behind the front badge.
Certain accessories that are fitted and integrated to Canbus wiring systems require programming using diagnostic tools and the EOBD port.
Live data is an important aspect of diagnostics. In some cases, such as this live throttle position data, the info itself might be irrelevant. Instead, you are looking for patterns, such as the throttle pedal movement being represented accurately on the graph. For measuring sensors outside of the EOBD socket, an oscilloscope is an invaluable tool.
Some generic tools might allow you to access specific ECU functions for maintenance work. For example, this one includes controlling the electric park brake ECU, which is essential for the safe replacement of friction pads.
Good-quality diagnostics will also direct you to the location of the EOBD socket on your specific car.
Water ingress into this socket might cause the ECU to assume that the component is faulty, while the real issue lies with the wiring.
More advanced diagnostics will provide information on wiring diagrams, component specifications and even part numbers.
Consider investing in other diagnostic tools, such as a pressure gauge (as shown), which gives an analogue reading of particulate filter pressures that can be compared against the data provided by the diagnostic equipment, as it may be corrupted by a faulty pressure sensor.
◀ Oscilloscopes are useful diagnostic tools, especially if you have a PRE-EOBD car. They test the input/ output signals of a component, but you need to interpret the on-screen display. Oscilloscopes are not cheap, but they are a good investment if you know how to use them.