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Old 12-24-2017, 03:26 PM   #4
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Join Date: Aug 2014
Location: Boulder, Colorado

Does the diag LED light up when you push the button with the probe not plugged into anything? If so, it means you have good power and ground to the diag box. If not, ground is under the button, power is under the LED. You can also touch the probe to ground to light up the LED.

If the 740 harness is like the 240 harnesses, then the pin 2 diag wire runs all the way to the LH ECU with no other connectors in the path (pin 6 goes direct to EZK). Since you're getting a CEL but pin 6 shows 1-1-1, the CEL must be from ECU. Find a chart of ECU fault codes -- only some of them will light up the CEL (CTS, AMM but not TPS IIRC).
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