Pcm not communicating

Ethan Teeters

New Member
Feb 20, 2020
1
0
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19
Albion Michigan
So I bought another mustang as a project... it's a 1999 v6 5-speed ford mustang. The car will crank but won't start. Also the fuel pump doesn't kick on. Theft light is flashing, and the pcm is not wanting to communicate to a snap on tablet. I first began to replace the fuel pump and filter, and nothing still didn't work.
Then I found out that the theft light was flashing. I had someone come out with a snap on tablet and we got a new key and started setting it up. But the pcm was not communicating with the tablet. So i went and got a brand new pcm for the car, installed it and it started to communicate.I ended up manually hooking the fuel pump up to a battery. To fix the fuel pump not kicking on. I Turned the key on and the fuel pump started working. The car started right up with the fuel pump manually connected to a battery and a brand new pcm. Turned car off and the pcm stopped communicating. Even kept the fuel pump hooked up to the battery but it wouldn't start. The theft light turned back on. I'm really stuck on what to do, I'm 17 and i only know so much. Please help :)
 
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alwayshi

Member
Feb 22, 2019
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Hawaii
I had a similar problem to this recently. Ended up being a bad CCRM. I’ll find the thread for you to sift through. Burns helped me diagnose and check a lot of stuff.
So before I post the thread. Check your fuses if not done so. And by check, I mean pull and literally check each one, then check for continuity and/or power
 
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wmburns

SN Certified Technician
Aug 14, 2009
5,878
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204
Houston Texas
Please understand there are several "conditions" that could cause your reported symptoms. The first recommendation I would like to give is to resist the urge to "part change" to a solution. Instead, perform some targeted tests and go where the results led.

Go though the "crank with no start" check list. Pay attention to what the check engine light is supposed to do during cranking. Pay attention to exactly what the theft light is supposed to do. Again, understand that a PCM power/ground problem can CAUSE an apparent anti-theft (PATS) problem.

Also note the role that fuses F2.34, F2.2, and F2.8 can play in this. Confirming the power state of these key fuses would put you way down the road to understanding where the problem really is.

Crank with no start check list:
 
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