Diagnostic Memory

The C-4 system is designed with a short-term memory. It will store a trouble code as long as the ignition switch is on. When it is turned off, the memory will be erased. To remember intermittent problems, and because some trouble codes do not register for 5-18 minutes after engine warmup, a long-term memory is sometimes needed. To create a long-term memory, connect the "S" terminal lead of the ECM to a battery positive source (such as fuse block cavity marked "GAUGES").

A long term memory is not factory connected because it will create a small drain on the battery during ignition off and could cause a discharged condition. When repairs are completed, disconnect this wire.