Electrically Heated Catalyst Monitoring

FUNCTION AND DIAGNOSIS

The heating of the electrically heated catalyst is only conducted at every engine start when numerous switch-on conditions are met and no faults are stored for the following ranges.

- CAN ECM
- CAN instrument cluster
- Output stage injection valve
- Misfire (Catalyst damage)
- Output stage secondary air injection pump
- Output stage secondary air injection valve
- Coolant temperature sensor
- Crankshaft sensor/reference point

The adjustment and the diagnostic for the heater of the electrically heated catalyst is conducted by a separate control unit directly communicating with the ECM.

If the heating-element is supplied by electrical current, it begins to glow. The heat generated by this process is let to a small catalyst located directly behind the heating-element. The heating-time is independent from the input parameters and has always the same duration.

The heating-current is compared as a diagnostic criteria (1.5 x standard) to a defined current threshold. If the heating-current decreases the defined threshold for a defined duration a relevant fault is stored and the MIL is illuminated during the next driving cycle.

Additionally to the above mentioned diagnostics further electrical diagnostics and plausibility-checks are conducted, which cause a break-off or a lock of the heating-cycle and a relevant fault storage in case of a fault

Both exhaust Systems are separately checked.