My wife was going home from work. When it died no lights on. It would turn over but not start. Put a new pump in. Had just changed the filter. But still nothing. I noticed the security light flashing so I put my scanner on it and all I get is a code saying no signal to the pats system. So is that the key or something else in the system. Also does anyone know what wires on the ecm relay do what and their voltages and amps. Just checking things out. Because I can't scan nothing else on it but the security system. Thanks

 

If the security light is flashing, then there's something wrong with the PATS system and no pump will solve that issue. You need to diagnose the PATS system, perhaps the pickup coil is bad or loose connection, that's where I would start unless there's a code pointing to something more specific.

To this end, I would highly suggest you get a proper scantool and order a DVD with the workshop manual if you're going to work on it yourself, you can get the workshop manual for 10-20 bucks on ebay.

Use FORScan (available on Android, iOS and Windows) to properly check the system with a cheap bluetooth scantool. (Or you could pull the trigger on a good one for 99 bucks, get the OBDLink MX if so OBDLink® MX Bluetooth | OBDLink® | OBD Solutions .)

 

The problem is "upstream" of the PATS subsystem, PATS cannot disable a vehicle that is already running.

Check for PCM power (the relay is a common failure). Observe and report the state of the check engine light and the digital odometer display when the key is first turned from OFF to RUN (not START).

 

No check engine light is on. Checked relay it was good. All fuses are good. The odometer has dashes on it. I did notice that sometimes most of the stuff on the instrument panel don't allways come on. I did put a 2amp fuse in a add a fuse link.and touched it to the signal side of the .ecm relay and everything worked. Didn't leave it on but for a couple of seconds.

 

Swap the PCM relay with another good known working one, like for wipers or something.

 

Any blown fuses?

 

Swapped relay. No blown fuses. Codes was u1262 and b1681.

 

U1262 is communication fault between PCM, GEM and other modules. In order to figure out which module is not communicating, you need a good scanner. A good bluetooth scanner with FORScan could do this.

Most likely it is the PCM not communicating. This can be bad wiring/connector, PCM not receiving power or dead PCM. I don't have the wiring diagram in front of me for 2001 Expedition, but checking voltage on the connector to the PCM would be the next step for ensuring that the PCM is receiving 12+ V on all the necessary pins

 

There are two communication networks running on the Expy. One is the standard corporate protocol network that runs on a twisted pair cable. IIRC, the only modules on the SCP are the PCM, the HEC (which is the instrument cluster), and the EATC (Electronic Automatic Temperature Control).


All the other modules run on the ISO network, which is a single wire network.


(ForScan will map out which modules the vehicle actually has and which network they live on.)


The U1262 is set when the SCP determines that an SCP message is missing.


The B1681 is saying that the PATS transceiver signal is missing.


I suspect that the missing PATS signal is why the vehicle has a no start condition (and probably caused the U1262). I don't think the 2001 has a starter interrupt, so the starter spins the engine with the fuel shut off.

But as SHO said, PATS won't disable a running engine, so I suspect you have another issue that caused it to die when your wife was driving it.

 

Correct me if I'm wrong, but isnt the PATS integral to the PCM? If I am correct on that, making sure the PCM is powered up would be an important thing to find out. Truck suddenly dying and then having these non-communicating codes does point to a PCM not powering up as it should.

 

The PATS module, which includes the transceiver, lives under the steering column shroud. When the ignition key is turned to start, the HEC wakes the PATS module. The PATS module sends out an RF signal. The transponder in the ignition key captures enough energy from that signal to allow it to send out the transponders ID code. (That's why the key doesn't require a battery.)


The PATS antenna captures the ID code and sends it over the SCP to the HEC. The HEC logic (software) lives within the HEC. The HEC communicates with the PCM over the SCP network. If they both agree or disagree that it is a valid ID code, the PCM either enables or disables the engine. (Some systems use a starter interrupt, some use a fuel interrupt.) (That's why the HEC and the PCM must be "married" so that they can agree.)


To your point, it is interesting that the PCM relay, the HEC and the PATS module are all powered by the same fuse: fuse #30 (30A) in the CJB.

 

What you're calling the "PATS module" is correctly called the "PATS tranceiver". It's basically an antenna for reading the RFID chip in the tranponder key. Earlier model Expys had a separate PATS module that performed the task of operating the transceiver and then sending appropriate authorization to the PCM when it was requested.

Both the U1262 and the B1681 DTCs originate from the HEC, not the PCM.

But we digress. This is not an example of a PATS problem, it is an example of the failure of the PCM to power up and to communicate with the HEC (this vehicle has no PATS module) as evidenced by the specific answers to the specific questions I posed (no CEL, dashes on odometer).

Focus on the PCM's operation. It MUST have power and ground in order to operate. Until you PROVE both of those are present, you're only guessing (and probably wrongly).

 

You didn't say if it's 4.6 or 5.4, but they look identical for the power supply to the PCM.

Grounding pins 3 (BK/WH power ground), 25 (LB/YE case ground), 51 (BK/WH power ground), 76 (BK/WH power ground), 103 (BK/WH power ground).

Power pins 55 (RD/WH Keep alive power, always on), 71 (RD vehicle power, 12+V when key on RUN), 97 (RD vehicle power, 12+V when key on RUN).

Check all these, i.e. place black probe on chassis/negative on battery and measure 12V on each power pin and see if it gets a good 12V, do the same with the red probe on battery positive then black probe to check each ground pin.

Here's a picture of the plug.

 

Ok thanks everyone. I am gonna check the pcm out. And a couple more things. It is a 5.4. Think I might head to the junk yard and pick up a few extra parts. I do have one last question on this one. The inside fuse box. Are there some fuses that are a negative fused system. Went through retesting everything. It was showing some of them as a negative use. I use the power probe to check voltage and it was showing it.

 

Never heard of such a thing.