A4 Mk1
| Principle and function |
| Principle |
| The over-enrichment of the mixture in the cold start phase produces a higher proportion of unburnt hydrocarbons in the exhaust gas. The secondary air system improves the afterburning (oxidation) process in the catalytic converter, and thus reduces toxic emissions. The heat generated by oxidisation accelerates the “light off” of the catalytic converter and significantly improves exhaust gas quality during warm-up. |
| Function |
| The engine control unit activates the secondary air pump motor -V101- via the secondary air pump relay -J299-. The stream of air from the secondary air pump opens the combination valve for secondary air and permits air to flow into the exhaust system upstream of the catalytic converter. |
| 1 - | Secondary air pump motor -V101- |
| q | Fitting location → Fig. |
| 2 - | Air cleaner |
| 3 - | Combination valve for secondary air system |
| q | Fitting location → Fig. |
| q | Removing and installing → Chapter |
| 4 - | Throttle valve module -J338- |
| 5 - | Secondary air pump relay -J299- |
| q | Fitting location → Fig. |
| 6 - | Simos control unit -J361- |
| q | Fitting location → Fig. |
| 7 - | Non-return valve |
| q | Installation position: as shown in illustration, the arrow points in direction of flow |
| 8 - | Secondary air inlet valve -N112- |
| q | Fitting location → Fig. |
| q | Checking → Chapter |
| 9 - | Intake manifold |
| 10 - | Cylinder head |
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