Theory Of Operation - BCM/RF Hub Module Interaction

WARNING: This page is about a different car, the 2024 RAM ProMaster EV. However, it is still accessible from the selected car via links, so may be relevant.

There are a few things that must take place before the starter relay can apply voltage to the starter. Below are some key points to check when diagnosing a no crank condition.

The BCM requires two signals from the RF HUB to verify the ignition is in the run or start position. The voltage on the Ignition Run Start Output circuit is one of these signals. It can be monitored in both the RF HUB and BCM data display screens as the Ignition Run/Start under the "Sensor" value. The run or start position voltage on this circuit should be at or close to Battery voltage.

Simultaneously the RF HUB busses the Ignition Run/Start status to the BCM. The BCM monitors the bussed input information as the secondary verification on the Ignition Run/Start status. The bussed messages can be monitored with the scan tool in both the RF HUB and BCM data display screens.

The Ignition Run Start Output circuit voltage and the bussed ignition run/start status message received by the BCM must agree to enable starting. Once the vehicle is started, the loss of only one ignition signal will not cause the vehicle to cycle off as long as the other feed still indicates a "run status".

The RF HUB also requires an input from the Gated park switch (hardwired) and the OK to start CAN Bus message from the TCM (Crank Enable).