Functional check in idle
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During a functional check while idling, the air ratios are checked on the basis of their behavior under different marginal conditions.
When idling, the air ratios are measured in a range from 1.5 to 8.
The following marginal conditions affect the air ratios:
- Exhaust-gas recirculation:
When exhaust-gas recirculation is active, the proportion of fresh air during combustion is lower, leading to a lower air ratio.
The exhaust-gas recirculation can be switched off for the purpose of the test, e.g. be entering a long continuous idle phase.
- Activating consumers:
Activating consumers increases the fuel quantity during combustion, leading to a lower air ratio.
The following graphic shows how marginal conditions can affect the air ratios when idling.
| Index | Explanation |
|---|---|
| 1 | Air ratios when exhaust-gas recirculation is active. |
| 2 | Air ratios when exhaust-gas recirculation is switched off. |
| 3 | Signal from oxygen sensor upstream of oxidation catalytic converter. |
| 4 | Signal from oxygen sensor downstream of oxidation catalytic converter. |
| 5 | No consumers activated. |
| 6 | Successive activation of consumers. |
| 7 | Consumer activated. |
| 8 | Air ratios level during idle with no consumers activated. |
| 9 | Air ratios level during idle with consumers activated. |