PCM issues

MRTHOMAS

MEMBER
2007 FORD TAURUS
3.0L
6 CYL
2WD
AUTOMATIC
100,000 MILES

I haven’t had much issues with it except normal wear and tear. I recently replaced the starter, alternator, battery, ignition switch. I use this car for work so it’s very important I get it back on the road by Friday when I go back. Long story short, I’ve checked all relays and they seem fine. I’ve checked all fuses and grounds and seem fine. I’ve tried a few tricks I have read about. But this car will just not crank. I’ve tried just about everything I can think of. I’m no mechanic but I’m not dumb when it comes to mechanical issues. It’s electrical issues that I’m not very good at diagnosing. Hence why I’m here. I can’t get this car to crank (engine turning) and it won’t start. I can’t hear the fuel pump turn on which leads me to believe it’s the PCM. Can someone point me in the right direction to figure out if it’s that or something I might have missed?

Also just a side note, I have no communication with obd scam tool (just a cheap one).

7 Replies

STEVE W.

MECHANIC
13,475 POSTS

Did it crank and run prior to the ignition switch replacement? Did you replace only the electronic switch or did it also include a new key cylinder and keys? If so did you have the new keys programmed into the anti-theft system. If not the first time you tried to start the engine with a non-registered key the system went into a lockout mode and will leave you with a brick for a car. An automotive locksmith should be able to get into the system and program the new keys in, however some of the Fords are harder than others in key programming.

What does it do when you turn the key on? Do you have power like lights, interior? Dash?

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Tuesday, November 19th, 2019 AT 4:56 PM

MRTHOMAS

MEMBER
4 POSTS

I’m sorry, I should’ve clarified this in the original post but the car ran perfectly fine with no issues like it normally did on Saturday, I parked it over the weekend and went to go start it on Monday with my remote starter that I always use, and it didn’t start, I went outside and tried using the key and it did absolutely nothing. Like I said in the original post, Everything seems fine to me. But that being said to answer your question, I have lights and everything else. The dash works the radio works the blower motor works, everything seems to work fine except when you go to start it it doesn’t want to crank. I don’t have a panic alarm and the key does not have a transponder in it. But like I said the OBD does not communicate which leads me to believe it has something to do with the PCM.

I also have tried unplugging the battery for a while and then hooking it back up and still have nothing.

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Tuesday, November 19th, 2019 AT 10:28 PM

STEVE W.

MECHANIC
13,475 POSTS

Is the remote start a factory item or an add on?
As a test of the entire starting system to be sure the starter and wiring isn't the issue here is a simple test. Go to the junction box by the radiator and pull the starter relay. Look on the relay to identify the terminal locations. Take a test light and connect it to a good ground. Use it to probe terminal 87. This is the power feed to the relay. The light should come on if the wiring and fuses are good.
Now have someone turn the key to the start position and check for power at terminal 85. If the fuses, wiring, ignition switch and park/neutral switch are all good the light should come on.
Now swap the test light over to battery positive. Now touch the light to terminal 30. If the wiring through the starter motor is OK the light should come on. The starter may even come on but it's doubtful.
Next have the key held in start and test terminal 86. The light should come on if the PCM is getting the start signal and is grounding the relay. If one of them fails we have a starting point. The last part of the test is to take a jumper wire and jump from terminal 87 to terminal 30. This should energize the starter and crank the engine if the starter and power through the system is good.

The fuel side is a bit more complex as it uses a fuel pump driver module instead of just a pump and switch. For it a scan tool is the best way to test it.
You mentioned the fuses seem fine. Take the test light and use it on the tabs on the top of the fuses with the key on. Be sure to test the fuses in the front fuse box under the hood as well as the box under the left side of the dash. Any fuse with power should light at both ends. If you find one that only lights on one side change it out as it's blown.
Let us know what you find doing these tests.

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Wednesday, November 20th, 2019 AT 11:03 AM

MRTHOMAS

MEMBER
4 POSTS

Well I did all of the tests you suggested and they all passed. However I did notice that certain fuses when I touched them with test light (not the ones you asked me to test but other random ones like PCM fuses and GEM logic, they were all either 2amp or 5amps. Except one which was a 20 amp I think) and it would crank the motor. Any clue as to why? Maybe a bad ground or something? Or is that just the PCM being stupid cause it’s probably bad?

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Friday, November 22nd, 2019 AT 12:17 PM

STEVE W.

MECHANIC
13,475 POSTS

Did the starter turn over when you used a jumper in place of the relay? And the light came on when you tried terminal 86 with the key on? If those are both yes then the PCM is getting the start signal and should be triggering the relay to activate the starter.
Without knowing which fuse it is it's hard to say why the starter motor turned.
What does the security light on the dash do? How about if you turn on all the lights and try the key? Do they dim or anything? I'm almost wondering if you have a bad battery cable or connection. To test for a bad cable is simple, take a pair of jumper cables, connect the black side to a good ground on the engine, then the other end to battery negative. Try the key, Now connect the clamp you put on the engine to a good ground on the chassis/body. Try the key. Now take the red cable, connect one end to the positive post on the starter, then connect the other end to battery positive. Try the key. If it starts with either of the first two it's a bad ground, last one = bad positive cable or connection.