Exhaust Emission System Diagnostics (Emission control - V8) (page 2 of 2)

In the case of a catalytic converter failure the following failure symptoms may be apparent: l MIL light on after 2 driving cycles (NAS market only). l High exhaust back pressure if catalyst partly melted. l Excessive emissions l Strong smell of H₂S (rotten eggs).

Oxygen sensor voltages can be monitored using 'Testbook', the approximate output voltage from the heated oxygen sensors with a warm engine at idle and with closed loop fuelling active are shown in the table below:

Mass air flow sensor and air temperature sensor The engine management ECM uses the mass air flow sensor to measure the mass of air entering the intake and interprets the data to determine the precise fuel quantity which needs to be injected to maintain the stoichiometric air:fuel ratio for the exhaust catalysts. If the mass air flow sensor fails, lambda control and idle speed control will be affected and the emission levels will not be maintained at the optimum level. If the device should fail and the ECM detects a fault, it invokes a software backup strategy. ENGINE MANAGEMENT SYSTEM - V8, DESCRIPTION AND OPERATION, Description - engine management.

The air temperature sensor is used by the engine management ECM to monitor the temperature of the inlet air. If the device fails, catalyst monitoring will be affected. The air temperature sensor in integral to the mass air flow sensor. ENGINE MANAGEMENT SYSTEM - V8, DESCRIPTION AND OPERATION, Description - engine management.

Throttle position sensor If the engine management ECM detects a throttle position sensor failure, it may indicate a blocked or restricted air intake filter. Failure symptoms may include: l Poor engine running and throttle response l Emission control failure l No closed loop idle speed control l Altitude adaption is incorrect

If a signal failure should occur, a default value is derived using data from the engine load and speed. ENGINE MANAGEMENT SYSTEM - V8, DESCRIPTION AND OPERATION, Description - engine management.

Atmospheric pressure will vary with altitude and have a resulting influence on the calculations performed by the ECM in determining the optimum engine operating conditions to minimise emissions. The following are approximate atmospheric pressures for the corresponding altitudes: l 0.96 bar at sea level l 0.70 bar at 2,750 m (9,000 ft.)