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Re: reading computer codes
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.
On all 1990–95 models 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.
Once the terminals have been connected, the ignition switch must be moved to the ON position with the engine not running.
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.
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 PCM 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.
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.
NOTE: The order of codes in the memory does not indicate the order of occurrence.
If there are no codes stored, but a driveability or emissions problem is evident, the system should be diagnosed by an experienced driveability technician.
If one or more codes are stored, record them. Refer to the applicable Diagnostic Code chart in this section.
Switch the ignition OFF when finished with code retrieval or scan tool readings.
NOTE: After making repairs, clear the trouble codes and operate the vehicle to see if it will reset, indicating further problems.
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The first hing I would do is look at the coolant temp sensor data on a scan tool. This will tell me what the computer is seeing. If it is reading something way different than it should I would unplug it and see what the value changes to. It should read -40F. if it reads anything other than there is a problem with wiring or the computer. If it does read -40 than I would likely replace the coolant temp sensor.
most dealers do not read fault codes just to make money
have the fault codes read and that will determine which exhaust sensors are faulty ( heated oxygen sensor in the exhaust manifold) or o2 ( oxygen sensor after the cat converter)
the reading will also show it there is a problem ECM
That is the difference between reading codes & reading the computer readings. The codes don't necessarily mean the part is bad, emissions, electrical shorts, vacuum leaks make sensors set codes. YOU MUST READ THE SENSOR READINGS>
The universal OBDII code reader came out in 1996 per government mandate.Before that time, OBDI was the first vehicles with computers, and every manufacture was doing their own thing and creating their own vehicle specific testers or using lights on the computer to read codes.So you will not be able to ready the codes on your pre '96 vehicle.You would have to take it to a shop that has the special equipment to read the codes or get a service manual with flow charts to walk you through reading the codes off the side of the computer.Hope this helps.Good luck :O)
1st step is to get the codes read from the computer, it is an OBD2 system, so it should tell you what it is seeing wrong. It will set a code whenever it is unable to compensate for a sensor reading that is out of limits. Most auto parts stores will read the codes for you for free. The codes the computer kicks out should point you in the right direction to figure out what is wrong with it.
the only way to turn this off is to connect the car to a ODB II computer and read the codes the computer has set or activited. In the US most auto parts stores will read the codes of your car and turn off your service engine soon light for free but to make the light go off for good you need to read the codes and fix the problems those codes point you to.