- Checking the Basics

Before considering the C-3 system as a source of engine performance, fuel economy or exhaust emission problems, normal diagnostic checks for a vehicle without C-3 must be performed. Engine and all related systems must be operating within specifications to ensure proper C-3 system operation.
All procedures must be performed as outlined to ensure accurate results. Although there are several charts associated with C-3 system diagnosis, if proper procedure is followed only a few charts are needed to prove that system is operating properly, and normally only 3 charts are needed to locate a malfunction.
The built-in self-diagnostic mode detects system malfunctions most likely to occur and displays these malfunctions as trouble codes through the ``Check Engine'' or ``Service Engine Soon'' lamp. However, this system does not detect all possible C-3 system malfunctions and the absence of a trouble code does not mean that the system is operating properly.





Due to the electronic system control and low system voltages, certain precautions must be taken to ensure accurate diagnosis and avoid system damage. Do not disconnect or connect electrical connectors with ignition on unless specifically instructed. Do not connect test equipment directly to ECM, except where noted, and never attempt to measure oxygen sensor output as sensor will be damaged.