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Year 1955 Manual Transmissions 75 Units
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Year 1964 327 ci / 300 HP 10,471 Units
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Year 1996 Coupe base Price $ 36,785
Recovering the C4 ECM / PCM Codes
The following applies to recovering the OBD-I (On Board Diagnostics) codes on the 1984 through 1993 model C4 Corvettes via the 12 pin ALDL connector located under the dash just to the right of the steering column.
1994 and 1995 C4s also had the OBD-I system but used a 16 pin access connector that would become standard for the OBD-II system used on 1996 and later Corvettes. For 1994 and later models, you will need to recover the codes using a special procedure involving the speedometer and the odometer as explained in the service manual or use a special diagnostic device known as a scan tool.
On Board Diagnostics
The 1984 through 1996 Corvette has an On Board Diagnostic (OBD) system which is part of the Electronic Control Module or ECM, (also known as Powertrain Control Module or PCM in 1994 and later Corvettes), plus a system of sensors located throughout the automobile. The ECM/PCM gathers input from the sensors and continuously changes the fuel/air mixture, timing and other engine and transmission parameters so as to optimize the operation of the automobile for the best compromise between performance, efficiency and exhaust emissions.
Any time a sensor's output exceeds a Hi / Lo reference parameter stored in a Programmable Read Only Memory (PROM) array in the ECM / PCM module, an error code is set and retained in the ECM / PCM memory.
This event causes the lighting of the Malfunction Indicator Lamp (MIL) on the "tell tale" panel (more commonly known as the "Check Engine" light) or the SYS (System) lamp located on the instrument panel above the speedometer on later C4 automobiles.
If the problem clears and remains cleared for 10 seconds, the light will extinguish however, the error code is still stored in the ECM / PCM memory.
Regardless of whether the problem is constant or intermittent, the error code can be recovered through a user friendly system involving the MIL (Check Engine) or SYS lamp.
To the immediate right of the steering column under the dash, you will find a multiple pin electrical connector. This connector is called the Assembly Line Data Link (ALDL).
From 1984 until the end of the 1993 model year a 12 pin ALDL was used. After that, a 16 pin ALDL connector was used. The 1994 and 1995 model year still used the OBD-I system even though they have 16 pin connectors. The 16 pin connector in the 1996 C4 is used for the much more complex OBD-II system and a scan tool is required to discover the OBD-II system's secrets.
The early ALDL connector has room for 12 pins however only 7 are populated and of those we are only interested in Pin "A" and "B" for this procedure.