Action Taken:
ECM clears all BCM data from ECM memory. ECM assumes that A/C clutch is on at all times and controls ISC motor operation accordingly. ECM turns on "SERVICE SOON" light. ECM tries to send "SERVICE SOON" message to BCM over data link.
The ECM and BCM share information through the ECM-BCM data link. The BCM is in control of data link and data is only transmitted at the BCM's request. Data is sent in 8 character words at a rate of 8192 characters per second. The data from the ECM to the BCM contains power steering pressure switch, park/neutral switch, 4th gear switch, engine running, and coolant temperature sensor information. The ECM/BCM data also includes coolant temperature sensor, RPM and injector pulse width information to control the cooling fans, display RPM, and calculate MPG for display. The BCM sends the ECM air conditioning status to be used for idle speed control and ambient temperature for use in VCC application and release.
Code EO47 is set in the ECM in the event of a data link failure. If it's a hard failure, the ECM will not be able to communicate with the BCM and Code B334 will be current. Code EO47 is current in the ECM but cannot be sent (displayed) to BCM because of data link fault. If data link fault is corrected, both Code E047 and B334 will be displayed as history codes.
Code E047 can only be displayed as an intermittent. If fault is present, Code B334 will be current. Diagnose problem using BCM CODE B334, LOSS OF ECM DATA chart. Refer to the DFI BCM TESTS/CODES article in this section. Three failures can result in a Code E047:
- Open in circuit No. 800/800H between ECM terminal C9 and data link. The symptoms will be: A - "SYSTEM PROBLEM" message on CCDIC panel. B - "SERVICE SOON" and "CHECK INFO CENTER" lights on. C - Diagnostics entered and "NO ECM DATA" is displayed on CCDIC panel. D - When repaired, diagnostics will show Code EO47 as history and Code B334 as current codes until key is cycled to off.
- Grounded circuit No. 800/800H from ECM terminal C9 to data link. Symptoms will be: A - "SYSTEM PROBLEM" message on CCDIC panel. B - "SERVICE SOON" light on. C - Speedometer is blank at instrument cluster. D - A/Cheater system goes to 75°F and defrost, cooling fan goes to high. E - Diagnostics disabled, "SYSTEM PROBLEM" message stays on CCDIC panel. F - When repaired, diagnostics will show Codes E047, B334, B335, B336 and B337 as history codes.
- Open ECM Memory Calibration (MEM-CAL) unit. Unit contains communications instructions for the ECM. Symptoms will be the same as grounded circuit No. 800/800H.