1.15.16.1 Diagnosis during cold start

During cold start (catalyst heating) it is checked whether there is a permanent deviation between the current idle speed and the setpoint idle speed.

Additionally it is necessary to take into account the condition of the ISC integrator.

The ISC integrator is a measurement for the regulated deviation to reach the setpoint idle speed and is limited to an upper and lower limit.

If the throttle valve opens too much it may happen that the idle speed rises above the fuel cut-off engine speed and the system starts oscillating. To cover this special case the number of detected fuel cut-offs during an idle phase is analyzed.

If...

• the deviation (positive) between setpoint and current idle speed (under speed) exceeds a calibrated threshold or
• the ISC integrator equals the upper maximum threshold limit and
• the engine load lies below a calibrated threshold,
• for a calibrated period of time, a minimum fault LLRKH will be set

If...

• the deviation (negative) of the current engine idle speed lies below a calibrated threshold and
• the ISC integrator equals the lower threshold limit or the ISC integrator has reached the system demanded limit and
• no fuel cut-off condition has been detected,

all for a calibrated period of time, a maximum fault LLRKH will be set

If the number of detected fuel cut-offs during this idle phase exceeds a calibrated threshold for a calibrated period of time, a maximum fault LLRKH will be set.