2003 Ford F150 Theft Light Flashing

This 2003 Ford F150 came in with the complaint that the engine would not fire up and run. The starter worked, the theft light flashes quickly and the odometer reads all dashes instead of numbers. Scanning the PCM found that it would not communicate with the scan tool. There was a code U1262 ( missing standard corporate protocol communication bus malfunction)  stored in the IPC/HEC (Instrument Panel Cluster /Hybrid Electronic Cluster).  Basically the IPC/HEC set a code because it knows that another computer module is not talking to it.  An interesting note about the flashing theft light. Turn the ignition switch to the run position and watch the theft light as it flashes quickly for one minute. After the 60 second period of the theft light flashing rapidly the light will go out. Then it may start flashing slowly in a pattern. One flash, a pause and then 6 quick flashes. the pattern will repeat. The pattern is a two digit code of one followed by a six. The code is a 16 and is equivalent to a U1147 or a U1262. I already had pulled the code U1262 with my scan tool.

All of the evidence is pointing to a problem with the PCM not communicating. The next step is to check the voltage on the red wire at the idle air control (IAC) solenoid assembly, the mass air flow (MAF) sensor or at any injector connector. with the ignition on. There should be a nominal 12 volts present. The reading I got was .378 volts.


The PCM power relay (pointing to below) supplies power to the red wire mentioned above. Installing a new relay restored battery voltage to the red wire circuits.


Testing the output signal of the PCM power relay can also be done at several fuses in the underhood fuse/relay box. Fuse number 18.


Fuse number  23.


Switched ignition power for terminal 86 of the relay comes from the #30 fuse (30 amp) in the central junction  box / interior fuse box.


I also replaced the fuel pump relay at the same time since it will likely fail in the near future.


The engine now started and ran, the theft light went out and the digital odometer reading was restored. With the mileage on this vehicle I should also point out that the odometer is sometimes just blank. That is a completely different problem and I have covered it here.




13 discussions on “2003 Ford F150 Theft Light Flashing”

  1. Thank you for your help! I followed your directions & the truck started up again. It was the fuel pump fuse located under the steering wheel column that was causing the problem, it had blown out. But it was acting as if the key was not programmed or the receiver was not recognizing the key.

  2. So I have a 2002 Ford F-150 4.6L V8 I’m looking for a new ECU would any computer from a 2002 Ford F-150 fit mine? Or is there like a year to year where they used the same computer like 2000-2003 or something like that?

  3. Yes they were fully powered the red light turned on when I checked them. With the keys I had a locksmith come and when he seen it he said he was sure that it was that the keys weren’t programmed so he did his thing and he ended up saying it wasn’t the keys could it be possible that it’s the computer that just gave up from one moment to another.

    1. Anything is possible. Looks like you will need to get someone local that is more familiar with the systems and has more tooling than your locksmith.

  4. I also have the same problem a few nights ago I got in my 2002 Ford F-150 and I started it as I was reversing I felt like I hit something well there was a lamp post behide me so I thought I hit it got out to check the damage and nothing so I thought it was weird as I went back to leave again I put it in gear and the truck is off even though I left it on so I turn it off with the key I go to turn it back on and it’s only cranking now. Now I have no clue what it is I had someone come check it out and he told me to get a locksmith to come and program my keys again. Well he comes out and he says he’s sure it’s the keys that aren’t programmed a few minutes go by and he says it’s the not keys that I should call someone to see if it’s the computer that just messed up. So if anyone has anything they might think it is that can be helpful.

    Ps I also called the guy who installed the alarm on my truck and he said it couldn’t be anything with the alarm.

    1. I would check to see if battery voltage is present at the IAC solenoid or an ignition coil with the key on. If it is not replace the PCM relay in the underhood fuse box. Very common for it to fail. The theft light will flash quickly and the odometer may display dashes instead of numbers.

      1. When the mechanic came that’s what he did he checked if voltage going to the IAC solenoid and he said everything was fine but I still went ahead and changed the PCM relay anyways and I try to crank it and it still won’t fire up the theft light is still on and the odometer is still showing dashes instead of a set of numbers.

        1. I am assuming that your truck has the 4.6 liter engine since you have not stated different. Check fuses 18 and 23 in the underhood fuse box to make sure that they are both good and powered with the ignition on. If okay try to start the engine and leave the key on. Watch the theft light. If it is flashing rapidly continue watching it and in about 60 seconds it will start to flash two digit trouble codes. Record the code and get back to me. Do you have access to scan tool to check codes in all modules?

          1. It is a 4.6 and I checked fuses 18 and 23 both were still good, I did what you told me which was to get the code from the flashing theft light and it says 1 5 1 5 over and over again. About the scanner when the mechanic come he had one but he said the computer wasn’t letting him scan anything.

          2. You did not state whether the fuses were fully powered with the ignition on? If they were not then the code is meaningless. If they were then the flashed code 15 indicates a problem with the key being used. It is either faulty or not programmed to the vehicle.

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