Having a major electrical gremlin in my 02 7.3. Driving down road, just quit like I shut it off. Everything seemed to be working but would not start. Cranks but no start. Upon closer examination I notice that the fuel pump is not running, jumper it , it works fine. Glow plugs light just stays on and plugs don't work. Gauges on dash reset when key turned on, but do not read anything. Except oil pressure gauge works. Tried AE to scan for codes, it cannot communicate with the pcm. Tried DP Infinity. It also cannot communicate. Pulled pcm plug and tested for power and ground. All power and ground pins have power or ground. Changed CPS, no difference. While key is on, the infinity powers but all the gauges are blank except the pyros which are independent of anything else. It was suggested that the fuel bowl heater can kill the pcm when it goes. SO unplugged that and put in a new pcm. No difference. Tried my pcm in another truck. Works fine. Tried new pcm in another truck, works fine. So can anyone give me a clue were to look or what is going on. I cant find anything wrong, yet in my truck my pcm is dead, or acting dead, has power and gets warm, but no signals come out. Help please

 

There is a 30 amp fuse in the fuse box under the hood to power the PCM. This is the fuse that blows when the fuel bowl shorts out. Also make sure the cigarette lighter fuse is OK.

 

I have an 02. There are no fuses under the hood, all are in the fuse panel in the cab and every fuse and relay on the board is good. As stated above, the pcm is receiving power at all the pins its supposed to, grounds as well. So not a fuse issue. Power goes into the pcm, but is lost between the pcm and the motor. I saw on the drawings that there is an auxillary powertrain control module after the pcm. Trying to find it to see if I can test it. Maybe it is blocking the signals from getting threw. At this point I can't find anything wrong. Im just going to test each pin one at a time, end to end to look for shorts. Then the dash harness as well. Something is stopping the pcm from functioning and I havn't a clue what.

 

[LINK]

The "auxillary powertrain control" is the Injector Driver Module - the item that drives the injector solenoids.

I see the tan wire with an orange trace and the pink wire with a light blue trace are your communication wires.

 

I continuity tested the communication wires from the usb port to the pcm. they are good. pcm to rest of motor I havnt got to yet. the wires you say, are they the idm signal wires or the pcm ones? I'm going to redo all my tests with the pcm in, probing the back of the pcm plug into the wires. That way I can trace all the pcm out bound signals to see if I'm losing any. which seems to be whats happening, sort of. Like stated the pcm has all its power and gets warm like it should, but no info comes out for the running of the truck. I'll start with the pcm to idm signals. The fuel pump is out too, so I'll check that next, then glow plugs and dash signals. That's all the stuff missing so I'll start there. That should take a few days. Lots of wires. eek

 

Just a note. All the stuff not working is because the pcm is either not turning them on, or the pcm signal is lost some were. I jumpered all the dead stuff and they all work fine, so its a signal or short issue. The idm is un testable so I'll check the wires first, if all checks out I might throw a new idm at it to be sure. wish you could test that stuff. But I don't see why the idm would stop pcm communications. I'm stumped. Also, I want to test the cps wires as the cps causes some weird gremlins. Only issue I have on that is the electrical drawings show the cps plug is a two wire system. Mine is a 3 wire plug and system and I'm not sure what goes were to test it. CPS is new so its ok

 

They go to the PCM, the IDM, and the instrument cluster.

That link in my previous post shows the three-wire CPS.

 

I cant see your link? I will look at the wires you said. Do you know there pcm pin numbers? Easier to find that way. Plus i can mark them off as i test. I do know the communication wire from usb to pcm is good. Im hoping the onez you said are the outgoing signals. Thats what i think is missing

 

found your link, thank you. will test now. the link was right under you picture so my brain assumed they were all one picture. Duh!

 

Look for a chafed wire in the steering column. Specifically the TCIL harness.

 

Ok, I will check the column. Can you un abbreviate that harness? Im not good at reading these diagrams, don't know which one you mean. If those wires can cause communication issues I wouldn't doubt it. My shifter is so loose I can't get 1st gear except in drive. Some times I have to jimmy the shifter to get the key out. Wish I could fix that too, but can't afford a column either. lol.

 

Don't see any chafed wires. The white block on the bottom with the big yellow wires coming out has a lot of taps from the alarm system guy. Checked the all out, soldered and good taps. Alarm works as should so ok there. I did try to take it out though just to be sure its not involved but theres a yellow cut and tapped into the alarm and I don't know were it went to re hook it with alarm out. So alarm stays in. I think it went to the fuse box, as there is a cut yellow there. I don't think it related as it immobilizes by killing the starter and setting off alarm. which Is working and when off the starter turns over fine. No other results to post at this time. Lots of wires to trace.

 

I know you said all the relays were OK but did you try swapping the one that controls the IDM and fuel pump? I know that one controls a lot of stuff, it is the same one the Cyclops anti theft system uses to disable the truck. If you are not sure which one I can go look at my 02 and post back. It could be there is a grounding issue as well, maybe at the relay?


Also, to be clear, you definitely have power to the fuse box? I know there is a connection on the fender behind the air box on 02-03 that supplies power to the fuses and relays and it is fairly common for it to degrade in snow/salt country. I know you said the PCM is powering up but if I recall there is more than one power source for the PCM.

 

I definitely have power. All my fuses work, and are good, and if you know nothing about the truck and turned on the key, you would have no clue anything is wrong unless you try to start. Dash and everything lights up and works and the gauges cycle to 0, only indication theres a problem is the glow plug light stays on, and the digital gauges on the infinity have no values, read nothing. They should have 0 until it reads a value, but they are blank. Only when you try to link to the pcm do you discover that it wont link and the running side is out. It does find the usb port because it works fine and the communications wire from it to the pcm is also fine. Its gotta be after the pcm. The relay you mention, is in the fuse box next to the pcm relay?? 302 and 303. Those both click, and the pcm gets power, so that one is good for sure. I havnt started testing key on pcm in yet. Alittle nervous because its the wires from the pcm to the idm I want to do first. Communication line first. But the idm supplies 115 volts to injector harness, so I'm alittle nervous of the probing wires on the plug while its live.

 

It is the relay with the blue tape on it in my picture. Without that relay I get the same symptoms you are having, no fuel pump, no gauges, WTS illuminates but no glow plugs. You might have a problem with that relay, its socket, or the circuit connected to it.