Code 12 is only the beginning of fault code reading process,it is not a Fault Code in itself.Here is how to retrieve the codes properly.Most parts stores will pull codes for FREE if you are having trouble getting them.Is the Check Engine light even illuminating here or are you only assuming that there should be codes when the engine runs poorly?

Listings of the trouble for the various engine control system covered here are located in this section. Remember that a code only points to the faulty circuit NOT necessarily to a faulty component. Loose, damaged or corroded connections may contribute to a fault code on a circuit when the sensor or component is operating properly. Be sure that the components are faulty before replacing them, especially the expensive ones.

The Assembly Line Diagnostic Link (ALDL) connector or Data Link Connector (DLC) may be located under the dash and sometimes covered with a plastic cover labeled DIAGNOSTIC CONNECTOR.

1. The diagnostic trouble codes can be read by grounding test terminal B. The terminal is most easily grounded by connecting it to terminal A (internal ECM ground). This is the terminal to the right of terminal B on the top row of the ALDL connector.

2. Once the terminals have been connected, the ignition switch must be moved to the ON position with the engine not running.

3. The Service Engine Soon or Check Engine light should be flashing. If it isn't, turn the ignition OFF and remove the jumper wire. Turn the ignition ON and confirm that light is now on. If it is not, replace the bulb and try again. If the bulb still will not light, or if it does not flash with the test terminal grounded, the system should be diagnosed by an experienced driveability technician. If the light is OK, proceed as follows.

4. The code(s) stored in memory may be read through counting the flashes of the dashboard warning lamp. The dash warning lamp should begin to flash Code 12. The code will display as one flash, a pause and two flashes. Code 12 is not a fault code. It is used as a system acknowledgment or handshake code; its presence indicates that the ECM can communicate as requested. Code 12 is used to begin every diagnostic sequence. Some vehicles also use Code 12 after all diagnostic codes have been sent.

Images available only to Customers.


Fig. 2: ALDL connector-1993-95 models

5. After Code 12 has been transmitted 3 times, the fault codes, if any, will each be transmitted 3 times. The codes are stored and transmitted in numeric order from lowest to highest.

The order of codes in the memory does not indicate the order of occurrence.

6. If there are no codes stored, but a driveability or emissions problem is evident, the system should be diagnosed by an experienced driveability technician.

7. If one or more codes are stored, record them. Refer to the applicable Diagnostic Code chart in this section.

8. Switch the ignition OFF when finished with code retrieval or scan tool readings.

After making repairs, clear the trouble codes and operate the vehicle to see if it will reset, indicating further problems.

Please click my ACCEPT button if this will be helpful,Thanx Dale and let me know how you make out here.Images available only to Customers.

"It is much wiser and cost efficient to ask a question than to stumble blindly through your auto repairs".Please Click Accept if my answer was helpful.