Circuit Description

The Class-II serial data line is used to communicate information between modules. Each module connected to the serial data line is assigned its own recognition code (address). This DTC is used to identify which modules are communicating. Modules communicate with each other by periodically sending State Of Health (SOH) messages.

When ignition switch is in RUN position, each module communicating on the serial data line sends a SOH message every 2 seconds (one second for PCM) to ensure that system is operating properly. When the Electronic Brake and Traction Control Module (EBTCM) stops communicating on the Class-II serial data line, such as EBTCM losing power or ground, the SOH message it normally sends on the serial data line every 2 seconds disappears. The instrument cluster which expects to receive that SOH message detects its absence and sets an internal DTC U1040 associated with the loss of SOH of the EBTCM, which is no longer communicating on the Class-II serial data line.

Conditions of setting DTC:

• Instrument cluster does not receive SOH message back from EBTCM. Instrument cluster retries the request 3 times, then sets the DTC.
• This DTC only sets if DTC B1982, B1983, U1300 or U1301 is not current in instrument cluster memory.