No CEL, No codes?

Went in for emissions test. When they plugged into the diagnostic port, the CEL lit. Trans and engine computer communication lost were the two codes.

I checked connections at the TCM under the dash and poked around under the hood checking ground strap continuity and stuff. Didn't find anything so I disconnected the battery for awhile to clear the codes.

Drove the truck 50-60 miles. Still no CEL so back to the sniffer station. As soon as they plugged in, CEL and same two codes. Whiskey Tango Foxtrot?

After about 20 miles of driving, the CEL went away by itself.

I dropped the truck off at a mechanic tonight to see what they can find out.

I'm feeling poor already.

Did you work (unplug and plug 3,4,5 times) all the connectors you can find to the PCM? Seems like it's intermittant. The mechanic will guess at answers, and then guess how much to charge$$$$$$$$$$$$$$$$$$$$$$$ And funny how when you trace stuff down yourself, 90% of the time it's the connector, but if you take it in, it is almost always an electronic component. After all, how much could they charge for cleaning a connector? But if a $200 part needs replacing too, then $200 labor sounds reasonable.

winterbeater said:

Did you work (unplug and plug 3,4,5 times) all the connectors you can find to the PCM? Seems like it's intermittant. The mechanic will guess at answers, and then guess how much to charge$$$$$$$$$$$$$$$$$$$$$$$ And funny how when you trace stuff down yourself, 90% of the time it's the connector, but if you take it in, it is almost always an electronic component. After all, how much could they charge for cleaning a connector? But if a $200 part needs replacing too, then $200 labor sounds reasonable.

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The two modules I worked the connectors on are the one above the gas pedal under the dash (TCM?) and the big flat aluminum thing behind the driver side headlight with three big connectors on it. I also checked the battery connections and I verified the battery ground to frame and the ground strap continuity with an ohm meter.

The thing that's weird to me is that the CEL only goes on when the emissions test plug is connected to the diagnostic port. And after driving for awhile, it resets itself. If it was an O2 sensor code or something, well, OK, but it's a computer communication code, so that makes me think the act of plugging into the diagnostic port is triggering the CEL, but I'm ignorant about the workings of this stuff.

I see what you're saying. I don't know -- something stupid..........do they plug it in when the key is off, or while it's running? If running, will they do it when it's off? Maybe try a different test station. When we had that testing crap in Michigan, the results would be way different depending where you went.

Its the test equipment. Find a different place.