Finding the root cause

18 November 2013  

By Garry Lovett

Temperature can also be used as a measure, as the exhaust temperature is often higher before the blockage and lower after. This method can be applied to ‘normal’ silencers but be careful – due to their function, catalysts and DPFs do cause a temperature change and this is not necessarily a fault. Many newer systems now have temperature sensors in the exhaust which potentially could be used as an indicator in conjunction with a scan tool, but this is not ideal.

From the scan tool perspective, manifold pressure (MAP) is a parameter that could be used, it is one of the main sensors used to calculate engine load. There are problems with this method though as the units of measurement shown on the tool can vary between manufacturers, making calculation of the actual pressure more complex and troublesome. It is far better to use a direct measure to diagnose a blocked exhaust.