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Autodata - Diagnostic Trouble Codes Fault locations and probable causes - 2004 edition

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Oscilloscope testing I<br />

Fig. 18<br />

Fig. 19<br />

EvapMstive ~mlsslon (EVAP) can-<br />

purge valve<br />

Fig. 20<br />

Fig. 21<br />

Serial data - amplitude, frequency, shape, pulse width <strong>and</strong> pattern<br />

Serial data signals will be generated by the engine control module (ECM), if it has a self-diagnosis facility - Fig. 21.<br />

By noting the pulse width, pattern <strong>and</strong> frequency, the short pulses can be counted in groups <strong>and</strong> interpreted a souble<br />

code, in this case 1223.<br />

The amplitude <strong>and</strong> shape remain constant <strong>and</strong> the pattern will be repeated until the trouble code has been erased.

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