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Discussion Starter · #1 ·
2017 E-450 Super Duty 6.8L Gas Engine.
I drove through an extreme dust plume. Unbeknownst, mice chewed a hole in the end cap of the air filter. The dust caused problems giving Error Codes: P-0171, P-0174 and P-0300.
AutoLink tester I/M readiness shows problems with FUE, CAT and EVAP.
Replaced air filter, the mass air sensor and added Lucas gas treatment. The engine seemed to return to normal. But the A/C wouldn’t work.
Cleared errors and drove about a 1000 miles to home. Checked upon arriving home and there were no additional error codes. Engine was difficult to start when cold, but perfect starts once warmed up.
As mentioned, the AC wouldn’t work on drive home and still doesn’t work.
I explained, in writing, this exact scenario to Ford Dealership. They said it needed a new throttle body… It was replaced and nothing changed. They said it needed a new fuel pump… It was replaced and nothing Changed.
A local mechanic, they said the Computer wasn’t sending ground to the A/C relay and I needed a new Computer.
I still don’t think that will fix the problem because something in the emissions system is not allowing the computer to send the ground to the A/C relay.
What would cause the computer to not send the ground to the A/C relay?
Thanks,
Mark
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Well I'm definitely no expert in anything, but mentioned mice had gotten into it, the first thing I would do it open it up find the wire harness for the AC compressor and start back tracing through the harness until you find the spot that the mice may have chewed through. You could also grab a wiring schematic for the electrical on your van, locate the ground wire on the compressor, unplug your main harness connector at the firewall find out which pin is the ground wire to the compressor and check for continuity. If you have continuity then more than likely something happened inside the PCM / ECU. Just my opinion, maybe others will chime in.
 

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Discussion Starter · #3 ·
Mike1962,
Thanks for the input. I've done lots of checking and can't find any additional rodent damage. However, I still have a nagging feeling the problem is with the original dust issue. The A/C went out as soon as the problem occurred.

I was referred to another mechanic today who specializes in auto electronics. In talking with him, he also suspects there's more to the dust problem such as other downstream sensors. I have to agree with him since the PCM is simply an isolation point. Meaning... just because the PCM is not sending the ground to the A/C relay doesn't automatically mean the PCM is defective. It quite possibly means the PCM is prevented from sending ground because another emission sensor is still indicating a problem.

Thanks for the info. I will continue to look.

Mark
 
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