Modern diagnosis for vehicles

Kunle shonaike

What comes to mind when you hear the statement, “Your vehicle needs a computer diagnosis or needs a scan to find the problem?” Do you envision a technician connecting the car to a big machine with flashing lights that “beeps” a few times then prints out a description of the problem and its solution? Unfortunately, it’s not that simple.

Modern electronic engine control systems “know” and monitor the operating parameters of every component. When the input from a sensor falls outside normal limits for too long, or the output signal to an actuator repeatedly fails to generate the expected result, the PCM stores a diagnostic trouble code.

If a stored code indicates a problem that may increase exhaust emissions, the PCM also illuminates the “check engine” light on the dash. However, many types of codes can be set with no indication to the driver.

To access DTCs, technicians connect a “scan” tool to a diagnostic link connector (popularly called DLC) that is commonly located under the driver’s side of the instrument panel. The scan tool displays any stored codes, and many motorists think that’s where diagnosis ends. They question why they should have to pay, sometimes dearly for such a simple procedure.

In reality, pulling trouble codes is just the first step in a computer diagnostic procedure. DTCs don’t tell one if a part is bad, they only indicate that the computer has seen something it didn’t expect in a particular circuit. The problem may be the part associated with the trouble code, but it could just as easily be a shorted or open circuit in the part’s electrical wiring.

Sometimes, trouble codes are set when there is nothing wrong with the engine control system. This happens when a mechanical problem, like a vacuum leak, creates engine operating conditions that cause a sensor to generate an out-of-spec signal. The PCM will then attempt to compensate, which may cause an actuator to operate outside its normal range, setting yet another trouble code!

To help pinpoint the problem, a technician must perform additional tests. These can range from mechanical checks, like engine compression, to more in-depth electronic diagnosis. One common operation involves using test equipment to access the engine control system network data stream. This allows the technician to view real-time sensor data and manually operate the system actuators.

The ability to determine which additional tests are needed, and to accurately interpret both test results and computer network data, comes from training and experience. Today’s technicians use vehicle computer diagnosis in much the same way surgeons employ medical testing. In both cases, combining test results with expert knowledge and skilled hands can lead to a diagnosis and a cure.

REACTIONS TO AUTOMEDICS

Thank you for educating motorists weekly. I drive a Toyota Corolla 1999 model, second-hand. I noticed that if I speed 80mph and above, its hand vibrates. I did wheel balancing and alignment four months ago. I use new tyres. Please advise me. Ganiyu

The problem is with the balancing or some steering parts are faulty. Any good alignment technician will inspect all the steering and suspension parts before carrying out alignment work on the car. I will advise that the tyre rim, loose hub bearing, faulty ball joint and tie-rod ends could also cause this problem. Also make sure a dynamic or computerised wheel balancer machine is used with the right weight.

I drive a Rover car 2003 model. The vehicle’s TC descends whenever I am on a slope level. What do I do?

TC stands for Traction Control, the light means that the traction control system is out of commission, you will need to run a scan on the vehicle traction system. The result will guide on what to do.

I noticed that my car (Honda Accord 1998-“baby boy”) loses RPM suddenly despite my pressing of the acceleration pedal when on a journey. Its engine restores whenever I press down the accelerator pedal. After sometime after changing to gears three or four, the problem will start all over again. Now, it happens erratically. I have not been able to notice any pattern. I recently changed the ATF and engine oil and even the plugs. I have also cleaned the IACV but the problem still exists. Akpan

I have a feeling the fault is with the transmission. My advice is that you should run a scan on the vehicle’s powertrain system, the result will guide on what to do.

Thank you for your deep education on modern vehicles. Why do 2004 Honda cars — EOD have air conditioner problems? Could it be factory fault? Kindly educate us as my vehicle’s air conditioner, compressor, condenser, evaporator and pipes have been replaced with new ones but gas leakage still occurs. Thanks. Christopher.

I have no recollection of the A/C system having such problem. I believe you need to get a good A/C technician to solve this problem.

I drive a Mitsubishi GDI 2001 model front wheel. I changed the engine seat and gear seat. From the day I changed all the seats, the vehicle still vibrates and when I put on the air conditioner, the vibration increases. What do you think is the problem? Odunsi

I believe the ignition timing is off. Let your mechanic check the timing and adjust as needed.

What do you think is wrong with my Mercedes ML350? It starts hard and I have changed the fuel pump and filter. Anonymous

Please run a scan on the vehicle. The result will guide on what to do.

The recommended pressure for Lexus GX 470 tyre size of 265\65\17 is 32psi while 44psi is inscribed on GT tyre of same size on the SUV. Please, kindly advise me on which to choose to stop the flashing tyre pressure warning light? Thanks. Olayide.

You have to go with the vehicle’s manufacturer specification of 32psi.

I drive a Toyota Sienna 2001/2002 model. I noticed that each time I start the car and put it in drive, it delays for sometimes before it moves and when on motion, it hardly changes until I release my leg from the acceleration before it could enter the next gear. What do you think is responsible for this? What can I do to rectify the fault(s)? Thanks. Charles.

The transmission is definitely faulty, but the easiest way to resolve the fault is to run a scan on the transmission. The result of the scan will guide you on what to do and how to resolve the problem.

I have at various times tried to reach you on the phone but unable to do so. Hence, my use of this medium. Please, since I purchased my Lexus GX 470, I have had this problem of the V-Trac lights on the instrument panel permanently on. All the mechanics who have worked on it do not seem to know the solution. I have continually been told that the fault is with the oxygen sensor. I have changed the sensor about six times.

Each time the sensor is changed, all the lights go off for as long as I do not refuel the car. The moment I refuel, the four lights come on. My mechanic continuously tells me to change the oxygen sensor. Please, does it mean that no solution can be found to this problem and what is the effect of changing the oxygen sensor because each time they are changed, the problem seems solved only for the lights to come on once I refuel the car.

I will really appreciate your advice in this regard. I bought the car in 2007 and I live in Benin. Thanks in anticipation. Aliyu

You have technically solved the problem by your explanation. Though your mechanic should have run a scan and the result of the scan would have guided him on what to do. Also, I believe the problem is with the EVAP system not the oxygen sensor. Please, still run a scan on the vehicle’s powertrain and send the result to me.

Can I use 245/70R16 tyre to replace 255/65R16 tyre. If yes, does it have any bad effect? Thanks for your assistance. Anonymous

The only effect is that the vehicle will be a little bit low to the ground.