DTC U034B: Software Incompatibility with Brake Booster Control: Description

Some engines are also equipped with a VSV. The VSV replaces the traditional vacuum check valve usually located in the brake booster. The VSV is located in the vacuum harness and is used for stop-start applications, to shut off air conditioning in warm or hot markets and to supply additional vacuum to the brake booster for brake performance during specific driving conditions.

The VSV is controlled by the PCM. When the demand for vacuum increases, the PCM grounds the VSV and vacuum is routed to the brake booster. The PCM must be configured correctly for VSV operation, if a VSV is installed on a vehicle and the PCM is not configured for a VSV, this DTC sets.