Principles Of Operation

Heated Steering Wheel

Principles of Operation

Heated Steering Wheel System Operation

When a heated steering wheel request is received, the Heated Steering Wheel Module (HSWM) applies voltage and ground to the steering wheel heating element (integral to the steering wheel). The steering wheel is heated to a temperature of approximately 28-34°C (82-94°F) and is maintained by the HSWM (Heated Steering Wheel Module) using a temperature sensor (integral to the steering wheel). The HSWM (Heated Steering Wheel Module) supplies a reference voltage and ground to the temperature sensor and monitors the voltage drop for controlling current flow to the heating element. The HSWM (Heated Steering Wheel Module) is designed to remain on, heating the steering wheel and maintaining temperature until switched OFF on the Front Display Interface Module (FDIM) or the ignition switch is turned OFF.

On all vehicles, slow heating between the 10 o'clock and 2 o'clock steering wheel hand positions is considered normal. On vehicles equipped with wood inserts in the steering wheel, there is no heating elements located under the inserts.

Heated Steering Wheel System Network Communication

The controls and indicators for the heated steering wheel system are in are located in the FDIM (Front Display Interface Module) (touch screen) only. The FDIM (Front Display Interface Module) does not communicate on any network and is connected directly to the Accessory Protocol Interface Module (APIM).

When the FDIM (Front Display Interface Module) controls are used, the APIM (Accessory Protocol Interface Module) sends a heated steering wheel request message to the HSWM (Heated Steering Wheel Module) using the following message path:

- The APIM (Accessory Protocol Interface Module) sends the request over the Infotainment Controller Area Network (I-CAN) to the Front Controls Interface Module (FCIM).

- The FCIM (Front Controls Interface Module) sends the request over the I-CAN (Infotainment Controller Area Network) to the Instrument Panel Cluster (IPC) module.

- The IPC (Instrument Panel Cluster) module then sends the request to the Body Control Module (BCM) over the High Speed Controller Area Network (HS-CAN).

- Lastly, the BCM (Body Control Module) sends the requests to the HSWM (Heated Steering Wheel Module) over the Medium Speed Controller Area Network (MS-CAN).

The messaging path is followed in reverse for status updates that need to be sent from the HSWM (Heated Steering Wheel Module) to the APIM (Accessory Protocol Interface Module).

Remote Start System Behavior

When the remote start feature is used, the heated steering wheel system may be configured, through the message center, to be activated by the HVAC module based on outside air temperature. During remote start, the outside air temperature is continually evaluated by the HVAC system and the heated steering wheel system activation changes if the outside air changes from cold to moderate or warm temperatures or back from moderate or warm to cold temperatures.

For cold ambient air temperatures (below 10°C (50°F)) the heated steering wheel activates if the Steering Wheel is set to Auto in the IPC (Instrument Panel Cluster) message center.

For moderate and warm ambient air temperatures (above 10°C (50°F)) the heated steering wheel does not activate.

Field-Effect Transistor (FET) Protection

A Field-Effect Transistor (FET) is a type of transistor, that used with module software, monitors and controls current flow on module outputs. The FET (Field-Effect Transistor) protection strategy is used to prevent module damage in the event of excessive current flow.

The HSWM (Heated Steering Wheel Module) utilizes an FET (Field-Effect Transistor) protective circuit strategy for its heated steering wheel element output. Output load (current level) is monitored for excessive current (typically short circuits) and is shut down (turns off the voltage or ground provided by the module) when a fault event is detected. A short circuit DTC is stored at the fault event and a cumulative counter is started.

When the demand for the output is no longer present, the module resets the FET (Field-Effect Transistor) circuit protection to allow the circuit to function. The next time the driver requests a circuit to activate that has been shut down by a previous short (FET (Field-Effect Transistor) protection) and the circuit is still shorted, the FET (Field-Effect Transistor) protection shuts off the circuit again and the cumulative counter advances.

When the excessive circuit load occurs often enough, the module shuts down the output until a repair procedure is carried out. The FET (Field-Effect Transistor) protected circuit has 3 predefined levels of short circuit tolerance based on the harmful effect of each circuit fault on the FET (Field-Effect Transistor) and the ability of the FET (Field-Effect Transistor) to withstand it. A module lifetime level of fault events is established based upon the durability of the FET (Field-Effect Transistor). If the total tolerance level is determined to be 600 fault events, the 3 predefined levels would be 200, 400 and 600 fault events.

When each tolerance level is reached, the short circuit DTC that was stored on the first failure cannot be cleared by a command to clear the DTCs. The module does not allow the DTC to be cleared or the circuit to be restored to normal operation until a successful self-test proves that the fault has been repaired. After the self-test has successfully completed (no on-demand DTCs present), DTC U1000:00 and the associated DTC (the DTC related to the shorted circuit) automatically clears and the circuit function returns.

When each level is reached, the DTC associated with the short circuit sets along with DTC U1000:00. These DTCs can be cleared using the module self-test, then the Clear DTC operation on the scan tool. The module never resets the fault event counter to zero and continues to advance the fault event counter as short circuit fault events occur.

If the number of short circuit fault events reach the third level, then DTCs U1000:00 and U3000:49 set along with the associated short circuit DTC. DTC U3000:49 cannot be cleared and a new module must be installed after the repair.