The increasing number of sensors deployed in cars calls for new design approaches in intra-vehicle electronic control unit (ECU) networks. ZigBee wireless sensor networks are seen as a good candidate technology, since they can provide high-performance short-range communication with low power consumption, as well as mesh networking capabilities. One of the main questions to answer before adoption of wireless technologies in a car is whether the performance delivered by these technologies is high enough. Firstly, a better understanding of the propagation characteristics in these environments is necessary. In addition, ZigBee sensor networks may experience interference from Bluetooth devices inside the car, commonly used for voice or data transfer applications, which may have a negative impact on the system performance. In this work, we study the performance of ZigBee sensor networks for intra-vehicle communications, in the presence of Bluetooth interference. In the first part, channel models are proposed for intra-vehicle communications in industrial, scientific and medical (ISM) 2.4-GHz band, obtained from channel measurements. In the second part, the system performance is evaluated in terms of packet error rate (PER) and average/peak packet latency, using measurements and calibrated simulations. The impact of topological and transmission parameters is studied, such as the sensor node locations or selected output power. Finally, recommendations for high performance operation are provided.