Engine Controls - Poor Performance in Diagnostic Mode

Bulletin No. T 83-44
File In Group 8
Number 28
Date Feb. '83
POOR PERFORMANCE IN DIAGNOSTIC MODE - 1982 DFI


Poor performance may occur in the diagnostic mode whenever a parameter value of "96" is being displayed on 1982 DFI-equipped vehicles. The normal operating mode is unaffected. This condition is most likely to be encountered while displaying barometric pressure (.0.3), coolant temperature (.0.4), or MAT temperature (.0.5). If a reading of 96 kPa or 96~C is encountered, the system outputs will remain unchanged regardless of sensor values until "96" no longer appears on the display.

Normal calculation of DFI system outputs is bypassed whenever the diagnostic display contains the mode number ".9.6" due to the diagnostic system's "output cycling" program. The ECM's cannot distinguish between ".9.6" and "96" on the displays.

Diagnostic codes which are set when the ECM recognizes an improper sensor value are set only in the normal operating mode and are not set while in the diagnostic mode. Likewise, "fail-soft" sensor values that are normally substituted to maintain vehicle operation when a code is set are not substituted in the diagnostic mode. Should an intermittent vehicle condition occur while in diagnostic mode, the service technician will not have all the diagnostic benefits normally provided by the DFI system. Therefore, while the parameter display can be very useful to technicians diagnosing specific conditions, customers who are aware of the diagnostic mode should be discouraged from operating the vehicle in this mode.