Fault Codes (ALDL connector):


The ALDL connector is found under the lower right hand hush panel - drivers side (except 1981/82).

F = T.C.C (if used) B = Diagnostic terminal
E = Serial data (connection to diagnostic tools) A = Ground
D = Service engine soon lamp (if used) G = Fuel pump
C = A.I.R (if used) M = Serial data (connection to diagnostic tools)

1982-1995 CORVETTE To obtain these codes the ALDL connector (on the right side of the lower hush panel - drivers side) you must Short together the ALDL pins A & B, perhaps using a paperclip, then count the flashes, each code is repeated 3 times, first off 3 x code 12 followed by any others held (repeated 3 times). When a fourth or subsequent code 12 is flashed that indicates the end of the code storage.

1981 Corvette (L81) These models had a very simple computerised ignition timing system, there is very little diagnostic information available with these cars, the GM shop manual would be recommended for this vehicle. The ALDL connector is under the centre console ash tray.

1982 Corvette (L83 Crossfire) These models had a more detailed ECM, akin to the later vehicles, the location of the ALDL connector is under the centre console ash tray, the diagnosis is similar to later vehicles, albeit more simplified.

1984 Corvette (L83 Crossfire) These models were similar to the 1982 Corvettes, but the diagnosis procedures are the same as the later vehicles. The ALDL connector is under the drivers side hush panel on the right side, this applies to all subsequent models.

1985 Corvette (L98 Tuned Port Injection) These models used the Mass Air flow system to determine engine air flow, using input from many of the other sensors the engine fuel and spark are varied according to load demands.

1986-1989 Corvette (L98 Tuned Port injection) Essentially the same as the previous model, but the introduction of ABS and the VATS system required additional computer units.

1990-1991 Corvettes(L98 Cross Fire Injection & LT5 32 valve) These models used the Speed density system to determine air flow. With the introduction of the 'wraparound' dash and subsequent additional options like FX3, the processing power required more computer units. Also note that the mileage of these and subsequent cars was held electronically in a non erasable form.

1992 and up Corvettes (LT1 & LT4-1996, & LT5 32 valve-up to 1995) These models were ever more sophisticated. The introduction of ASR, to compliment ABS, was made. The processing computers were changed in number over these years to attempt to consolidate servicing and complexity. These models had two oxygen sensors for each bank, enabling the ECM to control more even and accurate running. The speed density system was changed back to the MAF system in 94+ models. 95 & 96 models have a 3rd oxygen sensor post cat converter.

1996 CORVETTE The ALDL connection contains more pins and the diagnosis procedure is slightly different. More detailed diagnosis is required for the OBD-2 computer systems.

The above is intended as an overview of the system only. Please note codes can vary from year to year (1981 to 1996) so it's best to arm yourself with the correct factory workshop manual for your car. Eurovettes have these for sale. Please contact us and we will be happy to supply the workshop manual for your model.

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