•Most motor vehicles manufactured after 1996 are equipped with electronic fuel injection.
•As much as bad fuel may trigger the check engine through the lambda sensors, there's something else that mostly triggers the check engine light.
Image: BOOSTED AUTO
You are driving on the highway when suddenly the check engine light comes on. Out of panic, you contact your mechanic who is miles away to enquire why your check engine light is permanently on. He asks you whether you have fueled your car within the past 30 minutes. Your answer is yes. You both conclude that most probably the fuel must have been adulterated. You seem to believe this fact because it is the norm for Kenyan businessmen to use unscrupulous methods to multiply their income without justifying the service rendered.
Question number two; you ask him to clear the light. He advises you to switch off the car for a minute then start it again. You do as instructed, depending on how lucky you are, the light might go off or not. Assuming it fails to clear, now you must book an appointment for a scan tool to establish the main cause that could have triggered the light.
This brings us to answer the following questions
IS IT BAD FUEL THAT TRIGGERED THE CHECK ENGINE?
Ninety per cent of motor vehicles manufactured after 1996 are equipped with electronic fuel injection. An inbuilt self-diagnosis mechanism that utilizes a check engine light to relay information to the driver when one or more sensors on the vehicle's engine are not functioning well. This could be as a result of faulty sensors or just a malfunction detected within the engine. As much as bad fuel may trigger the check engine through the lambda sensors, there's something else that mostly triggers the check engine light after refueling which makes people unknowingly blame it on bad fuel. The culprit, in this case, is the fuel cap.
When fuel shakes in the tank it produces fumes that are trapped and recirculated back into the engine via special pressure operated valve called the purge control valve.
Failing to properly tighten the fuel cap makes the fuel fumes escape out of the tank causing a pressure decrease within the fuel tank. Once the control unit detects a lack of pressure effect at the purge valve, it automatically triggers the check engine. This will always happen moments after refueling hence for this obvious reason, people will always associate the check engine light with bad fuel even though it's not. The easiest way to solve this menace is simply by tightening the fuel cap or replacing it with a new seal if it is the seal that is worn out. The check engine light may not stay on for many days probably because on the next refueling, the fuel cap will be tightened properly.
HOW SAFE IS IT TO DRIVE WITH THE CHECK ENGINE LIGHT ON?
Check engine light limits the optimum vehicle performance. In simple terms, when a check engine is detected, the vehicle adapts to a limp home mode. The control unit limits the engine performance for the time being until the issue has been resolved. During this time instead of properly analysing all the sensors and giving the correct feedback to actuators, the computer works on a limited version that may cause increased fuel consumption and uncontrolled emissions which could damage the catalytic converter and the engine internals. On some cars, the limp home mode shuts off all other subsidiary systems triggering the rest of the lights i.e ABS lights, stability control lights, transmission lights, cruise control lights etc, mainly because the car can no longer depend on these systems’ proper operation.
Many people may argue out that they have driven their cars for years with a check engine light on without any effect but the truth is, normal operation of the car ceased the moment it permanently displayed the check engine. Warning lights on the vehicle's cluster are categorised into two;
-Yellow (orange) lights: any light in this colour indicates a fault within the vehicle's systems that need attention but the vehicle can still be driven. The attention may be needed perhaps when time allows but should not extend past your next service. Yellow lights may include check engine light, abs light steering angle sensor, stability control, etc
-Red lights: when you get a red light on the cluster the attention is needed instantly. In fact, on some occasions, the vehicle should be stopped and checked. Some of the red lights may include oil pressure light, battery light, brakes lights, timing belt light, airbag lights, safety belt light transmission oil temp lights etc. Whenever a light comes up in the above 2 categories, it means that the said system is off.
HOW TO CLEAR THE CODES WITHOUT THE SCAN TOOL/DIAGNOSIS
A scan tool is always the best way to read the vehicle’s faults and erase the memory from the vehicle's computer but in some situations, you may not have a scan tool especially when you have travelled away from urban areas.
The method given below does not apply to all the cars but it may come in handy. The essence is to clear the faults that could probably have been triggered by a malfunction in the operating system. If the fault clears then reoccurs within a short period then automatically it shows that there is a faulty sensor that needs replacement (in such cases a scan tool must be used to establish the faulty sensor).
- With the car switched off, the gear lever put to a neutral position, parking brake fully engaged
- Disconnect all the battery terminals starting with negative and then positive
-Switch the car on and off in short intervals of about one second at least 5 times
-Step on the brake pedal or press the horn or both for about 10 seconds. This is just to drain power from the control unit capacitors so that all the stored fault memory is fully erased.
-Turn the ignition key to an off position and reconnect the battery terminals starting with positive and then negative.
- Start the car and confirm if the check engine light is gone. If not, then the use of a scan tool is a must.
Once this process is successfully completed, the vehicle might idle erratically due to control unit reset but it should be back to normal running within a few minutes. This is normal even when a scan tool is used.
Never let your cluster turn into a Christmas tree full of lights of all colours when the car is in use.
The writer is the owner of Boosted Auto car repair shop