Intake manifold — heating (Audi 80 B4)

From the Mono-Motronic fuel injection unit, the air-fuel mixture enters the intake manifold and from there — into the combustion chamber of the cylinder. If the intake manifold pipes are cold, then a significant part of the mixture settles on their inner walls in the form of condensate. This leads to increased fuel consumption. This can be avoided by heating the intake manifold, which is switched on when starting a cold engine. The intake manifold heater, installed on cars with four-cylinder engines, has the shape of a "hedgehog", which is placed in the intake manifold (see illustration 7.0).



This shape of the heater was not chosen by chance. It allows to keep the dimensions small, but to increase the heating area. The intake manifold heater operates until the coolant temperature reaches approximately 65°C, and then switches off. The thermal switch, designated in the electrical diagrams as the coolant temperature sensor G62, informs the fuel injection control unit of the coolant temperature. Depending on the coolant temperature, the control unit supplies power to the intake manifold heater via a relay on the additional relay block under the instrument panel. As the coolant temperature increases, the intake manifold is heated by the coolant circulating through the outlet channel in the intake manifold.

Intake Manifold Heater - Check

1. Disconnect the heater power cable plug. The engine must be cold.

2. Connect one wire of the ohmmeter to the heater power wire, and the other to the "ground" (-). The ohmmeter should show 0.25 - 0.50 Ohm. This means that the "hedgehog" is normal. If you do not have an ohmmeter at hand to check the heater, you can check the heater as follows.

3. Remove the fuel injection unit. The engine must be cold.

4. Turn on the ignition and make sure that the "hedgehog" heats up. If the heater resistance is normal, but it does not work, then the relay may be faulty.