Ask the mechanic: What is OBD and how is it used?

The OBD system can regulate the vital car systems, detect faults and report them as well as be used to command and maintain some of the electronic components.

OBD is a term commonly used by mechanics but I have no idea what it means. Can you please break it down for me?  Peter

Hello Peter, OBD stands for On Board Diagnostics, which is a universal standardised computer system designed in most cars built before and after the 1990s. This system uses a network of sensors and control modules to monitor, track and communicate with vital car components and systems such as the engine, emission, transmission, brakes, steering and safety, among others. The OBD system can regulate the vital car systems, detect faults and report them as well as be used to command and maintain some of the electronic components. 

Pre-1990s cars had OBDI which was connected to a car specific console or under the dashboard port. This system had some capability and user limitations. The post 1990s OBDII was designed with a universal 16-pin port which is mostly fitted on the lower part of the dashboard under the steering wheel. 

This is where you connect OBDII diagnostic tools and scanners for remote diagnosis, analysis of actual values, actuation and maintenance of different components and systems. The more commonly used OBDII system is an important platform for any vehicle maintenance or repair by technicians today. 

This is because vehicles rely more on electronic components to improve the efficiency and performance of all their vital systems mentioned above. To learn how to use the OBDII diagnostic tools, you must understand how the different systems and components work or fail. Then, get practical appreciation of the connectivity to different car models and the evolution to the standard 16 pin connectivity.  

A technician must continuously learn about the evolution in the industry of OBDII diagnostic tools, their connectivity, speed and range of functions from simple reading and interpreting fault codes to activating and programming different systems and functions on the vehicles. This makes fault finding and repair faster and more accurate as car technology and OBD capability continues to evolve.

How can I give my car a bit of a lift?

Hello Paul, my car is very comfortable on smooth roads and over small stones, but it leans on corners, bangs a lot on very rough roads, bounces a bit, and sometimes scrapes its belly on the top of speed bumps. Can I easily increase its ground clearance?   Carol

Hello Carol, those are classic indicators of a suspension that is too soft for local road conditions, and/or that either the shock absorbers or the springs or both are defective.

First check that the shock absorbers (and even the springs) are in good working order. If not, then replacing them will improve the ride stability and very slightly increase clearance. The replacements can also have a stiffer rating, but not too hard. The shock ratings must remain compatible with the spring ratings.

If they are too far out of sync with each other, then either the shocks will not be strong enough and the springs will be able to “bounce” the wheels, or the springs will not be strong enough and the shocks will fail prematurely as they compensate beyond their design limits.

 If you want a very much harder setting, you will have to change both ratings.

The simplest way to increase clearance is to fit a slightly higher profile tyre with a bigger external diameter that will slightly raise the ride height (clearance) of the car. Again, the change cannot be too dramatic or there might not be enough room in the wheel arches for the bigger tyre. Also, a change in tyre diameter will slightly change the car’s gearing and cause a similar degree (perhaps five percent) of misread on your speedometer and odometer.

Clearance can also be increased by adjusting or changing the springs. The complexity and cost will depend on what type of springs your car has – generally coil springs, torsion bar springs or leaf springs.

The easiest to crank up are torsion bars. That can be done with a jack and a spanner. Coil springs need a spacer between the car body and their top mountings (or a longer replacement spring). Leaf springs can be fitted with longer shackles and/or have additional leaves. Your garage will know immediately, and give you advice on these various options.

Bear in mind a big change in the ride height can change the steering geometry and require adjustment to related components.

The better news is that small change will not cause that complication, and as the ground clearance of normal cars is not very large in the first place, a small increase can make a significant difference and might be all you need.

Help me diagnose this ailing Toyota Hiace

Hello Paul, I request that you explain a problem I have not understood concerning the Toyota Hiace 7L, 9L. When driving on a steep hill, it does not accelerate, and as a qualified driver, you could say the van is saying, ‘I cannot breathe.’ Why? Daniel 

Hello Daniel,  allow me to begin with some not-so-necessary feedback; the 7L and 9L Hiaces you refer to are not actually called that, those are local names for the Hiace H200 flat roof and high roof respectively. I know the etymology of the 7L and 9L, with the H100 “Shark “Series we had two common engine types; the 3L in the DX version and the 5L in the GL and Super GL. There were no further L engines developed after this, they were superseded by the KZ series, which in turn paved way for the KD series which is what most diesel H200s use. So, no, there is no such thing as a 7L or a 9L.

With that information shared, let us get to the root of your problem. Perhaps the van literally cannot breathe. Have you checked the air cleaner to see if it needs replacement? If not air, then maybe the fuel filter is the cause of the problem. If not the fuel filter, then perhaps the injectors are clogged (although this would cause a misfire rather than hesitation). Is the vehicle automatic? In that case, check the transmission.

There could be other reasons as well. Boost leak, dirty sensors and clogged exhaust gas recirculation, among others. However, if the Hiace is running the 1KD engine, then there could be one last issue; the turbo stepper motor. The 1KD uses a VGT - variable geometry turbo - controlled by an external actuator motor rather than dump valves and pneumatic waste gates (the one that gives the turbos their distinct whistle).

 The stepper motor is responsible for the variation in “variable geometry” and when it fails, which it does, it causes the vehicle to go into safe mode. How do you know a 1KD is in safe mode? It will not rev past 1500rpm. Sounds awfully familiar, right? 


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