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Chris (aka- Moose)
Chris (aka- Moose), Technician
Category: Ford
Satisfied Customers: 46039
Experience:  16 years experience
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OK I'm going to take a chance here as one tech before told

Customer Question

OK I'm going to take a chance here as one tech before told me to do evrything I had done, then posted pictures from the service manual of pinpoint tests(which I already have) and said take it to the dealer which I explained was 150 miles away. Here is what I have done and what's going on. First I had the switch light on all the time. I replaced all the sensors and then the speaker. The speaker made the light go off. The 2 inside sensors work, the 2 outside ones do not. I replaced the outside ones, same thing. I switched the inside sensors to the outside with the same result--inside work-outside do not. I replaced the PAM--no change. I replaced the switch, no change. I replaced the wiring harness to the sensors-no change. The drivers outside sensor will go off momentarily if I stick my finger over it for a few seconds. The outside sensors do tick. I've looked around for pinched wires, broken wires, etc with no luck. On a general OBD II scan no codes. I have an Auto Enginuity scanner that hooks to a laptop and will scan the parking system abs, etc. It comes up with the message that it cannot communicate with the parking module. As you might guess, I am about to pull my hair out.
Submitted: 1 year ago.
Category: Ford
Expert:  Chris (aka- Moose) replied 1 year ago.

Let me know if you need the wire diagrams for this circuit. A no communication concern indicates the module is bad, or has wiring issues on the power or ground or communication wires. Have you tested those with a volt ohm meter?

You want a excellent 5 star answer & I would like to be rated the same for providing it. Consider I don't know your skill level & I can't see, smell, hear, or touch the vehicle. It may take a few back and forth replies. Try your best to respond with good detail so I can do the same. I normally log in at 3pm and work late. A rating is required. Your rating me, what I type. I am not an employee of this website, nor have control over the fees or the time it took to get a response. If you rate negative or not at all you still paid, but I get nothing. I want you pleased with me and my efforts, so let me know if your experience here has come up short.

Thanks Chris

Customer: replied 1 year ago.
I have wiring diagrams and the full service manual. Since I replaced the parking module with the new one and I have the exact same symptoms present, I took that as pretty good evidence (though not 100%) that it is not the module. I am obviously getting power to all the sensors since they tick. My reasoning is that I'm not getting a return signal or at least not enough to complete the alarm circuit in the module or the module is not getting enough power. The fact that I can put my finger over the driver outside sensor and it will eventually beep--but only for a second or so, makes me think there is a bad ground. I have searched all over the place. I bought this truck in Nov 14 and it was from New york. I bought it online so I didn't know about the rust which I have pretty much removed and repaired. I found a grounding strap rusted through on the rt side which I replaced but have found nothing else. I have checked the fuse which is ok and would be as I expect since there is power in the circuit as the 2 inside sensors work properly. I am having difficulty testing the wiring harness where it connects to the PAM. I have 3 voltmeters and all the probes are too big to touch the pins in the connector. I have taken a piece of copper wire and placed in the connector site I want to check and then use that as my contact point. I also pulled the connector in the tailight just to be sure there was no corrosion, etc since that connector branches off to eventually give power to the sensor wiring harness. Then I get this module communication error with this scanner. And since the module, switch, pam, and speaker have all been replaced, all that leaves me with is wiring-correct? I have pulled off the step plates on the carpet at the bottom of the doors and find no pinched or broken wires. I have done all this on the passenger side since that is where all the wiring leads. According to one diagram, there is supposed to be a ground from the license plate/trailer hitch circuit to the driver side frame rail. Of course, the spot it would be at is right where the gas tank is against the frame rail. I have felt up there but I do not feel any wire or grounding bolt there and there is no junction on the wiring I can find where it would split off to connect to a grounding point anyway. The wiring as it goes forward on the driver's side seems intact and undamaged which I would also expect since it attaches at one point to the fuel tank unit and I would assume I would have issues with gauges, fuel pump or something.My skill level is this;I am a dentist so I am good with my hands, think very logically as to cause and effect, and I catch on quickly.My dad taught me a fair amount of things about cars growing up and I am mechanically inclined. This is my second Excursion and they have been my hobbies as well as primary driver. I had a minor in physics in college so I can read wiring diagrams some but not as well as I would like. I can use a volt meter fairly well though I am not an expert. For example I'm having trouble wrapping my head around one of the point tests where you test resistance between pin 3 circuit 57 on the harness and against a ground...doesn't make sense to me. The biggest mechanical job I've done is I replaced my front leaf springs by myself. I do brakes , I've put in stereos and amps.etc. Basically I've been able to eliminate a lot of potential issues but testing the wiring--especially since I got the communication error from the scanner-has got me stumped.
Expert:  Chris (aka- Moose) replied 1 year ago.

The CKP is used for the ignition spark. The CMP is used for injector pulse. The CMP does not effect the fuel pump relay, the PCM and VLCM does that. Can you verify the PCM is grounding the VLCM with the key on. Below is a diagram if needed.

Customer: replied 1 year ago.
I believe you sent this to the wrong person
Expert:  Chris (aka- Moose) replied 1 year ago.

That I did, that was for the previous customer I was helping and for some reason it sent it to both of you.

Expert:  Chris (aka- Moose) replied 1 year ago.

Lets not chase wiring all over the vehicle. Slide a paper clip in beside the power and ground pins at the PAM so you can connect your tool there and see if you get battery voltage and no resistance to ground. Then we can follow the wiring if either of these fail. Can you do that?

Customer: replied 1 year ago.
You are talking about power and ground on harness correct? Make a u shaped connector out of a paper clip and connect power and ground--then measure voltage. across the clip??. I know setting resistance on the meter but where do I put the probes checking resistance for the ground. This is the one that gave me a conceptual problem. Easy to measure resistance at either end of a piece of wire, I get that. If I measure resistance between power and ground with a clip, Im getting the resistance of the paper clip aren't I?
Customer: replied 1 year ago.
this is what I got:
Harness to ground on body boltThis is what I could measure following my diagnostic sheets so far.Pin 1 (Voltage) 11.1 volts
Pin 9 (Voltage) 9.67 to 9.77 volts measured several times 2 different multimeters
Pin 3 (Resistance) .5 ohms-also checked multiple times with 2 multimeters
Expert:  Chris (aka- Moose) replied 1 year ago.

I am talking about power and ground at the connector on the PAM. The paper clip is straight slide in beside the power pin for the first test then beside the ground pin for the next test.

Pin 1 LB/BK is supposed to be battery voltage

Pin 3 BK is supposed to have no resistance to another ground pint.

The first wire coming out of the harness at the PAM, when following it from the PAM connector, is going to be the ground for the PAM.

Customer: replied 1 year ago.
U see my readings?
Expert:  Chris (aka- Moose) replied 1 year ago.

Pin 3 was the only one out of specs form your readings.

Customer: replied 1 year ago.
what do I do now?
Expert:  Chris (aka- Moose) replied 1 year ago.

Remove that ground connection, and sand it and retest. It needs to have 0.0 ohms of resistance on this ground wire to another ground location.

Customer: replied 1 year ago.
Do I pull it out of the connector?
Expert:  Chris (aka- Moose) replied 1 year ago.

You unbolt it from the body where the ground for the PAM comes from.

Customer: replied 1 year ago.
Where the heck is that----I've been trying to figure that out?...or can I splice on to the ground wire out of the connector and run a new ground wire to something??
Expert:  Chris (aka- Moose) replied 1 year ago.

The first wire coming out of the harness at the PAM, when following it from the PAM connector, is going to be the ground for the PAM. Below is an image.

Customer: replied 1 year ago.
OK but you don't know where the grounding bolt is??
Customer: replied 1 year ago.
Everything is wrapped in that binding tape
Customer: replied 1 year ago.
I followed the ground which is not present at the tailight connector harness. There is one place I see it going up to the speaker-which works. The wiring diagram I have says the ground is at the right rear corner of the vehicle which I have yet to see.The split going the other way runs under the big trim panel to the rt rear door which I'm not chasing since I've already pulled the door plates. Since the 2 inner sensors work that tells me the wiring to those is fine. What must be a problem is the wiring that is common to the outer sensors but not the inner--correct? the switch operates--simple on/off power to the system. Pin 3 on my troubleshooting guide says resistance has to be < 5 ohms which it is... .5 ohms. Pin 9 to ground is < 10 volts which it then says to repair circuit 140--which I have no clue what that is. Pin 9 is labeled "reverse input" going to exterior light system--I assume backup lights--all lights work. I think I am ready to shoot the PAM with my .45. This is insane
Expert:  Chris (aka- Moose) replied 1 year ago.

I posted an image pointing to where the ground wire is bolted to the body.

Circuit 140 BK/PK goes to the TR sensor and its the power that tells the PAM when your in reverse.

Customer: replied 1 year ago.
I promise you there is no bolt and there is no ground at that point. The harness wiring joins with 4 other sets of wires. One is a ground to the back of the blower motor--best I can feel.That one is about twice the guage as the others feeding into the junction. I don't suppose they would ground to the back of the blower motor would they??? One goes to the tailghts, one goes to the power point and one goes forward under the plastic panel. That's it. I have a picture but I can't paste it. The junction looks just like the diagram--there is just no ground wiregoing to a grounding bolt
Expert:  Chris (aka- Moose) replied 1 year ago.

I am just not seeing any progression occurring between you and I and this vehicle. We are pretty much stuck without a scan tool. I think its best I opt out and let someone else give this a shot. Best of luck and Thanks for letting me try.

Customer: replied 1 year ago.
someone else will contact me?
Customer: replied 1 year ago.
remember I have a scan tool that reads the parking module, abs, etc--AutoEnginueity scanner that works through my laptop-not one of those chinese trinkets. It says it cannot communicate with the module.
Customer: replied 1 year ago.
Thanks for trying
Customer: replied 1 year ago.
Bought the X in Nov. Back up on/off switch light was on. A 4 sensors seems bad--no ticking Replaced all 4 sensors--light still on, not working. Replaced the speaker, light goes off and the 2 center sensors work, the outer ones do not. I swapped them inside to outside, same deal so all 4 sensors are good--verified with a conductance wand. Thought it had to be the PAM. Found a used one. Ordered it, put it in, exactly the same result--inside works, outside do not.I replaced the on/off button. I replaced the bumper harness to the sensors with a new one-same result.I bought an Auto Enginuity Scanner which will read the parking module and several other expanded circuits as I paid extra for those options. When I run the scanner, everything checks out EXCEPT it says "cannot communicate with parking module". I did discover if I put my finger over the driver side outside sensor for a few seconds it will beep----once. I checked the power pin in the PAM connector--10.77 volts. Measured twice with 2 different multimeters. Resistance on ground wire is .5 ohms. That's where I am at
Customer: replied 1 year ago.
Also, I have tried to find the grounding bolt but it is nowhere that I can find