The Data Communications Link (DCL) is a wiring system that allows the sharing of information between the Electronic Engine Control System (EEC- IV), the Message Center Control Assembly (MCCA) and the Cluster Control Assembly (CCA) located in the electronic instrument cluster panel by using a common link (DCL).
The EEC-IV system transmits the following information through the DCL to the CCA and MCCA: Engine rpm.
Engine coolant temperature.
EEC-IV malfunction indication.
The CCA transmits the following information through the DCL to the MCCA: Fuel level.
Cluster display temperature.
Battery voltage warning.
Oil pressure warning.
Vehicle in Accessory/Run (ACC/RUN) mode.
Engine temperature warning.
Charging system warning.
There are two EEC-IV, DCL strategies. One covers the 49-state application, the other covers California. The California strategy uses the EEC-IV system to transmit Malfunction Indicator Lamp (MIL) information to the MCCA. The MCCA uses MIL information to generate a CHECK ENGINE warning in the event of an engine sensor failure.
In the event of a DCL failure, an alternating message of CHECK ENGINE then CHECK DCL is displayed on the MCCA.
Always check the fuses and relays first. If those check out, then check all the wiring and connectors. With a vehicle this old, it isn't uncommon to find wires that have frayed/broken/burned, and/or connectors that've worked their way loose.
If everything checks out, then suspect the computer. But don't just replace it. Check the input/output wires to see if the computer is actually accepting inputs and giving outputs according to spec. If not, then the computer is bad.