Engine Management Systems (page 2 of 2)

The MIL/Service Engine Soon warning lamp within the instrument pack utilises an amber LED and a clear legend. If an emission related fault is detected by the engine management system, the ECM will illuminate the LED providing the driver with a visible warning.

The warning lamp will illuminate whenever the vehicle is driven until the fault is repaired, and the ECM fault code memory is cleared using “TestBook”.

When the ignition is switched on, the ECM carries out a self-test function of the lamp. The lamp will illuminate for approximately 3 seconds then extinguish if no faults exist. If a fault is present, the lamp will be extinguished for 1 second before illuminating again to indicate a fault exists. If the MIL lamp doesn't illuminate when the ignition is first switched on, the warning lamp bulb in the instrument pack needs to be replaced; refer to the relevant Workshop Manual.

There are two configurations of the legend for the warning lamp:

• NAS and Canada = SERVICE ENGINE SOON text.
• All other markets = MIL SAE J1930 (engine) symbol.

The MIL will illuminate to indicate a EURO-3 type failure under the following conditions:

• A fault resulting in cylinder cutout (Misfire Detection). In order to protect the catalytic converter

from damage, the MIL lamp will flash immediately to alert the driver to the problem, and

remain flashing for as long as the fault is present.

• An emission related component failure. The MIL lamp will be illuminated if the fault persists

for more than two drive cycles.

• The engine control module (ECM) detects a “self-test” fault.

When the OBD system detects a fault for the first time, the corresponding trouble code is stored in the memory of the ECM. The MIL lamp is not activated unless the fault involves misfire, in which case the MIL lamp is activated immediately and remains flashing as long as the misfire fault is current. On OBD-II, this type of fault is termed a 'Type A' fault and is considered the most serious. When a Type A code is set, the OBD-II system also stores a history code, failure record and freeze frame data to help diagnosis of the problem.

If the emission related fault occurs again on the second drive cycle, the fault is stored in memory, and if the fault is present on the third drive cycle the MIL lamp is activated (i.e. when the same emission related fault has been confirmed, the MIL lamp is activated). On OBD-II, this type of fault is termed a 'Type B' fault and is considered to be a less critical emissions problem. The same fault must occur at least once on two consecutive trips before the MIL lamp comes on. If the fault doesn't recur on the second drive cycle, the MIL lamp stays off. If a Type B fault is registered on the second drive cycle, as well as MIL lamp illumination, a history code, failure record and freeze frame data are stored in ECM memory the same as for Type A faults.

If the second drive cycle is not completed so that a specific component is not checked, the third drive cycle is treated as if it were the second drive cycle.

If the emission-related fault is sporadic, the MIL lamp will only light up if the fault is registered in two complete successive driving cycles. The MIL light stays off if the fault fails to re-occur in the third successive driving cycle.