1 Multiplexed Electrical System Service Manual Important Notes Instrumentation Service Information describing how to remove, disassemble, and reinstall instrumentation components is located on ServiceNet. Before attempting any instrumentation repairs, the technician should have a complete understanding of the procedures described in ServiceNet. The simulate function within ESA can provide a valuable diagnosis tool. To ensure safe operation, certain CECU outputs are not accessible for simulation such as: cruise control, engine oil pressure and the park brake switch. Simulation of gauges is also not permitted if the engine is running.
This manual contains service manual information covering vehicles equipped with software version "CECU3 with Chassis Node" (P30-1011). For vehicles with prior CECU software versions (such as: "CECU3 with Chassis Node" (P30-1009), CECU3 (P30-1008), ICU (P30-1003), and CECU/CECU2 (P30-1002)) refer to earlier publications. Replacing the CECU results in the odometer being reset. Take appropriate action to record the vehicle miles prior to removing the CECU. CAUTION Interrupting the communication or power supply during a control unit reflash could result in hardware damage.
When replacing a chassis node, disconnect the batteries and do not reconnect them until node installation and all wiring connections are complete. A new chassis node and the CECU need to be powered up simultaneously during the node's first power cycle; otherwise a fault code message will appear in the main instrument cluster between the speedometer and tachometer. This message indicates that the CECU is not recognizing the proper communication with the chassis node. ESA recognizes when a software update is required on a connected vehicle. If for some reason the user chooses not to reflash the control unit, ESA triggers a warning display.
The LCD backlighting of the speedometer and outside air temperature blink for 1 minute. The warning is triggered at every key-on of the vehicle until the required update is performed to alert the operator or other technicians that a vehicle reflash is required. NAMUX 4 incorporates software in the CECU along with software in the instrument cluster. These software versions will often be linked together which will require both units to get updated should the other get updated. ESA will prompt the user if such a requirement is needed. ESA automatically identifies the version of CECU hardware when connected, and only permits software downloads that are applicable for that control unit.
Software versions are not backwards compatible; a vehicle is rendered inoperative if a CECU without the correct software version is installed. Check the program menu within ESA to see if an inoperative feature is disabled. This is very important when diagnosing an inoperative physical gauge on a CECU equipped vehicle. The gauge may have been previously disabled. 1 - 2 PM819023/KM815057 (08/14/2012)