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| After the three code 12 flashes, you will either get an error
code (or codes) or you will get another string of code 12 flashes
if there are no trouble codes stored. All codes are repeated three
times with a long pause between each code group so (for instance)
you could recover a string like this: 12, 12, 12, 36, 36, 36,
44, 44, 44, 12, 12, 12. In this example, your OBD has stored error
codes indicating that the Mass Air Flow burn off circuit has exceed
the Hi/Lo limits (Code 36) and that the Exhaust is to lean (Code
44). Whether or not this means that the sensor is bad or that
the parameter it measures has truly been exceeded is yet to be
determined however, you do know that the PROM based limits for
these two sensors have been exceeded. |
| If the "Check Engine / System" light is on when the
engine is running (during normal, driving operation in other words),
the condition(s) are currently present; if the light is not on
during normal operation, the limits were exceeded at some point
in time and the event was recorded in memory but the reading has
since returned to the normal operating range. Once you have determine
the error code situation, you can set about troubleshooting the
problem or you can take your vehicle to a Corvette repair shop,
tell the technician what you have found in the OBD system and
perhaps somewhat shorten the repair time. |
| Remember to remove the shorting device from the connector after
you have read the codes. |
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| To clear the codes from memory, remove the negative battery
cable for a minimum of 10 seconds. Very
Important: Make absolutely certain the ignition key is
turned to the off position. You run the very real risk
of destroying the ECM/PCM module if you connect the battery with
the ignition switch turned on. |
| Disconnecting the battery will clear all stored codes but it
will also clear the radio button presets, clock, trip odometer,
average gas mileage memory, power seat memory (if you have that
option) and anything else that stores something in memory. Your
ECM/PCM computer will also have to relearn your driving habits
again and adjust the timing/mixture/exhaust emissions to your
driving style. |
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| The central point to keep in mind when troubleshooting the codes
is there is no reason to automatically believe a sensor has failed.
It is possible that a sensor itself is exhibiting a hard or a
intermittent failure but it is more likely that a connector has
gotten dirty, a wire has broken or some underlying problem is
present and the sensor has done it's job. |
| For instance, a Mass Air Flow (MAF) error code is often a dirty
connector at the MAF sensor as opposed to a bad sensor. Similarly,
a code indicating a lean condition can be timing, fuel delivery
or dirty/plugged injectors. The codes are normally a symptom,
not the disease. |
| Do not immediately buy a new sensor in hopes that will fix the
problem. Look into the problem a bit more first using the links
from the code table as your guide and consider buying a scan tool
so you can determine exactly what your ECM/PCM is being told by
the various sensors and---just as important---how it is reacting
to the sensor inputs. |
| The table which follows lists the error (trouble) codes which
can be stored and recovered using the pin A/B technique explained
above. To learn some possible causes for the codes, click on the
code number. |
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