Chevy Error codes

What is error code 12 - "Diagnostic Mode" mean? I have a 88 Chevy Blazer and the service engine light comes on once in a while and that is the
error I get when I short the two contacts. Thanks
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It means, "I'm in diagnostic mode", "The Codes that follow are error codes". 12, 12, 12, short pause, 12, 12, 12, long pause. Means "I'm in diagnostic mode", "There are no error codes", "I'm still in diagnostic mode".
jrdad wrote:

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In article

Error code 12 means "no ignition reference pulses received by the ECM."
Since the conditions are that the engine is not running, there will not be any ignition reference pulses.
Diagnostic Mode; There are a number of diagnostic modes available depending on the resistive value placed between pins A and B of the ALDL. When you short the ALDL with a jumper, you are in the zero K ohms mode, using different resistor values such as 3.9K ohms or 10K ohms or open will allow different diagnostic modes to be activated by the ECM
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are there any references to this? what "different" modes of diagnostics are available?
never heard this before.
TIA.
C.B.
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So does that mean I need to get a resisitor to check it out or is everything ok? It only comes on if I drive it for a long period of time.
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I got it now, have to wait until the 12,12,12 is over. I have a 32 now, BARO circuit low
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