When diagnosing catalytic converter faults, it is vitally important to use a full 4-gas analyser test, and that technicians don't just use a standard MOT 2-gas test.
Our customers still tell us that the catalytic converter is at fault, by reading the 4 gasses could show a range of faults, one being that there is an air leak between the exhaust manifold and the first lambda sensor.
Watch the following video that was filmed at a garage in Wiltshire showing how to fully diagnose an air leak:
An MOT pass using a 2-gas analyser test would show a CO reading of less than 0.2 and a Hydrocarbon level of less than 200 PPM (parts per million).
But if you used a 4 gas analyser test to check that everything was working correctly, the readings would show a CO level of less than 0.2, Hyrdocarbon levels of less than 15 PPM, a CO2 of 13.5 or greater and O2 levels of less than 0.2.
Misfire?
The other most common fault we hear about through our dedicated technical team is where every now and again, a shot of O2 (air) passes through the catalytic converter caused by a misfire for example.
The vehicle's rear Lambda Sensor will pick up the higher O2 reading and switch on the Engine Management light. When a diagnostics tool is plugged in, it will show the catalytic converter is working below efficiency.
By using a 4-gas analyser test, you can identify the fault.
If the values are correct (CO < 0.2, CO2 13.5, HC <15PPM and O2 < 0.2), it is an intermittent fault, and not one caused by the catalytic converter.
