Circuit Description

The brake booster pressure sensor measures the negative air pressure or vacuum in the brake booster assembly. The engine control module (ECM) supplies the following circuits to the brake booster pressure sensor:

• A 5-volt reference circuit
• A signal circuit
• A low reference circuit

During engine running conditions, the brake booster pressure sensor signal circuit voltage varies, depending on the vacuum reserve internal to the brake booster. If the ECM detects that the brake booster vacuum is less than the intake manifold vacuum, then DTC P0556 sets.