How to Read Your Trouble Codes

About This How-to
Author: moonwell
Added: 07.19.03
Updated: 02.27.04
Discuss (16)
Find out what the "Check Engine" light really means - Applies to all 1982-94 J-Bodies

Is you check engine light on? Does it flash on and off intermittently? This means that there is probably a problem with one of the computer-controlled sensors controlling various parts of your car. These codes are store in the ECM’s memory. The ECM is the computer that controls your car. Before you take your car to a mechanic, you can easily find out what these codes mean yourself, and possibly fix it without paying for a costly mechanic! The most common trouble code seems to be number 13, the Oxygen sensor. Read below for info on how to retrieve these codes.


How To Do It

Step 1

To extract this information from the ECM memory, you must use a short jumper wire, or paperclip to ground a TEST terminal on the Assembly Line Diagnostic Link ALDL. This terminal is part of an electrical connector located under the dashboard by the steering column. There may be a small plate covering the connector that must be pried out of place to provide access to the terminals

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Step 2

With the connector exposed to view, push one end of the jumper wire into the TEST terminal and the other end into the GROUND terminal. These are the only two connectors with metal inside that are right next to each other. Do NOT start the engine with the TEST terminal grounded!

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Step 3

Turn the ignition to the “On” position, but don’t start the engine. The “CHECK ENGINE” or “SERVICE ENGINE SOON” light should flash Trouble Code 12, indication that the diagnostic system is working. Code 12 will consist of one flash, followed by a short pause, then two flashes in quick succession. After a longer pause, the code will repeat itself two more times, for a total of three

Step 4

If no other codes have been stored, Code 12 will continue to repeat itself until the jumper wire is disconnected. If additional Trouble Codes have been stored, they will follow Code 12, repeating 3 times before moving on

Step 5

Once the code(s) have been noted, use the identification table below to locate the source of the fault. Note: Whenever the battery cable is disconnected, all stored Trouble Codes in the ECM are erased. Be aware of this before you disconnect the battery.

Be advised. Damage to the ECM, PROM CAL-PAK or MEM-CAL calibration unit or related components can be damaged if you are careless with this procedure. I assume no responsibility for any damage;)

Step 6

Look up your code on the table below


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