Secondary Air Monitoring
4. SECONDARY AIR MONITORINGSec (e) (5)
Secondary Air System (based on linear - lambda sensor): Flow check
P0491/P0492, P0411
General Description:
The diagnosis is used to check if the minimum secondary air flow is available to warm up the catalyst, thus detecting a damaged pump, blocked valve or disconnected tube.
The diagnosis consists of two steps:
Step 1:
First the operative-readiness of the lambda-sensors must be reached. The mixture is then checked to determine if it is in a lean lambda-range for a defined number of monitoring cycles.
The diagnosis and secondary-air operation may be interrupted due to high engine speeds or engine-load ranges, because the flow of secondary air is then too low for catalyst heating and diagnosis.
Step 2:
After completion of the secondary air function, the result of step 1 must be validated. If the number of monitoring cycles is reached the lambda controller is used to check if the mixture is in a "normal" (non lean) lambda-range thereby ensuring no lean-problem is present.
Monitoring Conditions
The following enable conditions must be met for secondary air system monitoring:
- Secondary air pump is on
- Oxygen sensors (front state) are on
- Engine coolant temperature at first start is within acceptable limits
- Mass air flow is within acceptable limits
- Engine speed is within acceptable limits
- Air mass is within acceptable limits
- Engine state overrun fuel cut off is not active
- Engine state overrun is not active
- Ambient temperature is not too low
- Transient injection time correction (wall-applied film) is within acceptable limits
- Measured lambda is not too lean
Flowchart : Pump - electrical diagnosis
P2258, P2257, P0418
