I have 2004 f150 super c lariat the problem has been intermitant at first the guages would work then i turned it on and while driving they would turn on and off also odometer would read nothing as well this was intermittent but seems to be separate from guage malfunction. Rpm, speedometer and i think temp the only guage forsure that still worked was gas. Also one day the truck accesories would not turn off had to pull batt term.(we had heavy rain that week) All problems stopped for a week truck ran perfect! Different problems came back now truck key when turned off wont stop engine have to pull fuse. Truck accesories stay on heat radio head lights. Engine/ accesories run while key is out. Had to disconnect batt overnight. Truck will not turn over unless i hook batt up with key in on pos if i hook up with key in off pos truck wont start. Truck rarely turns off now but will run rough when key is removed. Cats where removed (earlyier time no relation) but engine light should be on always because of this it is not on now. So guages have been consistantly working and odometer, just cant get it to turn off and wondering why the cluster is not showing engine light. Ive changed fuel pump module driver by spare tire was very badly corroded. Recently changed cops. Ive checked all relays fuses. Also another thing in this time frame i think 3 times now the key has turned everything off but when i returned to my truck lights radio heat etc accesories have been on??? Has anyone had this prob??? Is it ignition switch? Would contacts on ingnition effect if guage cluster shows engine light on cluster??

 

I assume you have a New Body Style 04 and not a heritage. I would say start by getting a set of wiring diagrams for the truck, I purchased a dealer wiring manual on eBay for like $50 (just make sure you get the right manual F150 vs F150 heritage) but BBB Industries is a good tool as well (and its free).

The Check engine light is illuminated by the instrument cluster if it is instructed to do so by the PCM over the CAN Bus Network. The Oil pressure, voltmeter, and Fuel level are the only hard wired gauges, Tachometer, Speedometer, Odometer, Coolant Temp, MIL, Charging System Fault Indicator, ABS Indicator, 4x4 Indicators, and the Cruise Control indicator all come over the CAN Bus Network. Sounds like there could be an intermittent CAN Bus Fault, but that shouldn't prevent the ignition switch from shutting the engine & accessories down. Other than Catalyst efficiency codes due to the missing cats, are there any other codes in the PCM?

It could be the ignition switch keeping things on when it shouldn't be, but it could also be something back feeding power into the CJB's "Hot in Start/Run" Bus. Which fuse did you pull to shut the truck off?

 

Thank you for your reply.. So I tried to scan it at two different dealers they said they couldnt connect because of a short or fault. Thinking your on to something with can bus but would that stop the truck from starting or stopping i wonder. I forgot to mention it was putting my truck into engine failsafe mode but that has stopped for couple weeks i thought that was maybe a bad cops I installed but engine would run fine then bam engine fail safe mode as well with guages going crazy made me think pcm but thinking maybe water got into can bus area im not familar with that Ill look into it today. The pretty sure prob is not in pcm i unplugged the 3 big connectors and short is still occuring. Looking into can bus now thanks again!

 

The key switch controls the pcm power relay which controls dash cluster fuel pump etc . Can you pull pcm relay and will engine shutdown ? Pcm relay could be welded closed . There is a fuse to it you can try that as well . My diags are 05 .

 

So im leaning towards ignition switch. I took it out and manually turned switch or collar inside that as well was intermitant did that twice installed and removed key switch now it seems to turn on and off fine...looking for a way to get into contacts for ignition?? Thinking they might be damaged or dirty thing that bothers me is the big rain a couple weeks ago happen to be a coinsedence? Maybe the fuel pump module driver I changed yesterday was the problem and in cause back feed into ingnition contacts made then dirty??? Or maybe its coinsendece lol??

 

Thanks for reply..yesterday I swapped relays around no change. Im thinking something inside key switch but when i manual turned it with screw driver truck remained on. Iam i missing something that switch is just a secured key switch that turns the inside collar so if i bypassed it by useing screw driver why is the problem still there. Is there a way to get to the contacts inside?

 

I doubt the PCM power relay is the issue if the radio and other accessories are affected. The Ignition switch is a likely candidate for the starting/ not shutting down issues, however i'm not sure how it could cause a CAN communication issue. I suspect you may be dealing with 2 separate issues, especially since the instrument cluster issues arose first then the switching issues seem to have come later.

Unfortunately, i think you need to remove the steering wheel to access the ignition switch, or at least you have to to access the multi function switch. Maybe someone with more experience in this area can chime in, if not ill check my service manuals when I get home from work.

 

I removed steering column found theres a plastic rotating switch that controls on acc and start its on the left side opposite key side thinking this is the problem looking for part name now lol. It looks like the ignition switch has a little rod that goes through steering column key switch i think is ok... Im stuck now though everything is fine now so I cant go any further will update if problem happens again thanks for everyones comments. Does anyone know that part name or know if this sounds like the root of the problem?

 

did you figure this out.i have same problem and figured mine out

 

Fuel pump module located under rear axle it's part of the starting circuit mine was corroded and you could visually see damage also I changed the brake module ford located it in a terrible spot your drivers side tire covers the module in water etc the brake module harness connector needed cleaning as well

 

Hey Krazzy man56! What did your issue turn out to be. I am fighting this same issue and the unplugging the fuel pump module under the spare tire did not shut the truck off (until ran out fuel). I swapped out the ignition switch, no difference, swapped the relay, no difference. Pulling the PCM relay shuts everything down so something is keeping it energized.

Appreciate it, thanks!

 

The Fpdm is a known problem for a back feed . When water gets in there it causes crazy symptoms .After market items can cause back feeds . Evidently the run bus is being kept hot to hold pcm relay . New head units, stereo's/remote start etc . Its going to take some testing to find it. Start by pulling wires to added stuff .
One way to stop a backfeed is to put a heavy diode in the path . I say heavy but one that is easily big enough to carry the load is what's needed. We had to do this on some equipment at work to stop backfeeds.
Occasionally we did have trouble with some relays sticking closed ,some bad contacts ,some became magnetized .

 

Thanks Redfishtd! I will do some further digging.