Engine Management
Secondary Air TechnologySecondary Air System and On-Board Diagnostics (OBD)
On American on-board diagnostics, the function of the secondary air system is monitored with the aid of the lambda control. Two different methods are used in this case:
With European on-board diagnostics, called EOBD, the secondary air system is only checked with regard to the electric connection of the secondary air pump, but not for its effect. An incorrectly functioning secondary air system is therefore often only detected by an unusual whistling noise from the secondary air pump or by a varying idle speed in cold running phase.
Troubleshooting
Due to the fact that the actual cause of damage often remains unnoticed during the repair, the secondary air pump is consequently only replaced. The origin of the damage remains on the vehicle, however, and may cause a further failure of the secondary air pump. The actual cause is frequently due to the ingress of moisture and dirt into the secondary air pump on the suction-side or exhaust-side. A secondary air pump should really be installed as high and dry as possible, but due to the absence of such locations, car manufacturers often place the secondary air pump behind one of the front wheel housings, i.e. low and damp. Moisture and dirt have no problem getting in, especially if the pump is provided with its own filter integrated into the housing or if the induction pipe is not tight. For this reason, the filter and induction pipe should always be checked when replacing the secondary air pump to see whether dirt and water have accumulated there. Right: 'Dirty' secondary air pump interior |
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Before vehicles were equipped with component monitoring systems, the failure of a component in the secondary air system often remained almost unnoticed. However, since the introduction of on-board diagnostic systems, known as "OBD", every malfunction is "a case for the repair shop".
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