This months repair looks at exhaust gas emissions testing.

The car in question is a Fiat Cinquecento Sporting 1.1 litre. The little Fiat had failed the exhaust emissions test at MOT time. When dealing with electronic issues on cars we always follow a set procedure. This routine has been developed over many years.

The first area we look at is the cars engine management computer. In theory if the system detects a fault with the electronic control of the engine it will store a diagnostic code. This code can then be used has a guide to direct us to the problem area. Once in this area we can carry out further testing to pinpoint the fault.

Unfortunately the Fiat had no stored codes to use has a guide. In the absence of any codes I decided to take a closer look at the exhaust emissions print out. This printout gives the information from the emissions test. The four gases that are tested are CO, CO2, O2, HC. 

CO = Carbon monoxide  CO2 = Carbon dioxide  O2 = Oxygen  HC = Hydrocarbons.

After looking at the printout I could see that the O2 and CO where slightly above their limits. The next test involved the use of a digital oscilloscope. The scope is used to test electronic components in great detail. Most people will have seen oscilloscopes being used in hospitals. It stands at the side of the bed and measures pulse and heart rate via wires connected to the patients body. The scope in the garage works in just the same way, but my patients are cars and not people.

With the scope connected to the cars oxygen sensor it could be seen switching between 200mv and 800mv at a rate of about 1 hertz. With this single piece of information the diagnosis was complete. I didn't need to carry out any more testing, this one test had proved the engine was functioning correctly.

So how did we fix the car. Well the high O2 level was caused my nothing more than a leak on the exhaust system and the slightly high CO reading was fixed by adding fuel system cleaner directly into the inlet manifold via a special delivery system. The fuel system cleaner will clean the fuel lines, inlet manifold, fuel injectors, valves, cylinder head, oxygen sensor and catalytic converter.

The little Fiat went on to pass its MOT test and the owner reported back that the car had never run as well or as smooth. For me thats just a bonus...................

ProTec Fuel system cleaner.


The fuel system cleaner being drawn into cars engine.