Desperately seeking sag

[TPro]

SAG, did you receive my email? I need some help in the worst way.

 

[ENafziger]

Anything we can help with???

 

[TPro]

I have an 04 cr that won't communicate with my scanner (snapon modis), won't power

up the in tank lift pump, won't power up the gauges. No 5volt reference on all

applicable sensors, whick are all disconnected now. We have good battery power to the

ecm connectors, have tested all grounds. I'm very hesistant to blame the ECM as they

are very dependable and very expensive. The only information I have is Mitchell On Demand. We cannot find a PCM on this truck , I'm assuming that this year (or half year)

model incorporates PCM functions thru the ECM. Hence my search for SAG as I've read

his posts for many years and know he's a dealer tech (and a good one). Any other

techs out there have ideas? TIA. . Tim Propes

 

[TCDiesel]

Yep... its the PDC... See if the scanner can connect to ABS module or Front control Module and report Back (FCM/BCM).

 

[cerberusiam]

Probably the front controle module as it is the link to the ECU.



An 04 of any kind will have the PCM functions integrated into the ECU.



First thing to try is disconnect the fan harness. If the fan clutch shorts the FCM will shut down power to a lot of the sensors and inputs.



You might have to disconnect the batteries for 30 minutes or so to drain the any capcitors and allow it to reset.

 

[TPro]

Yes, we have communication with Front Control Module, ABS, airbag. I thought the

FCM controlled lighting, as this one shows light circuit problems in rear (harnesses

disconnected). Does it have any communication with the ECM? Could this be the

culprit?

 

[TPro]

Also have stored code 'FCM-Loss of JTEC, J1850 message, and FCM-Loss of CNN.

J1850 message. Thanks, guys

 

[cerberusiam]

Big harness connector on the firewall, thats the J1850 bus connection to the data port and cluster. It will sometimes loose continuity inside the connector. Unplug it, spray it out with electrical contact cleaner and re-seat it.



The FCM is the load supply for the circuits. The ECU is reading the back non-load side of the circutis to detemrine continuity, and commanding power on\off dependign on the readings. If the ECU senses a short it will knock out circuits to keep things from frying. The FCM is a controller with digital and mechanical relays that can and will go bad at times. Some of the relays can be unsoldered and replaced but the internals can't. Make sure all the ground points are solid and clean or you will chase ghosts forever. Make sure all battery cables are clean and tight, and, other power connections are clean and tight. Load test the batteries to make sure they are hoilding. A bad battery will cause no end of issues.



Make sure to umplug the fan clutch harness as it will shut down multiple circuits and cause a no start condition.

 

[TPro]

Great information, thanks a bunch. When you say FCM, aren't you referring to the

TIPM? I thought the Front Control Module controlled lighting, wipers, etc.

 

[cerberusiam]

TIPM is an 06+ item. The earlier trucks have a FCM and PDC that together handle the power distribution and control. You can replace them seperately. The TIPM is a single unit and has to be replaced as a single unit. Instead of $300 or so for each unit you get to pay $7-800 for the TIPM. Gotta love integration.

 

[seafish]

Here is a recent TDR thread with pix that describes the differences between TIPM and PDC/FCM--

https://www.turbodieselregister.com...29485-how-many-years-has-dodge-used-tipm.html

 

[sag2]

I have an 04 cr that won't communicate with my scanner (snapon modis), won't power

up the in tank lift pump, won't power up the gauges. No 5volt reference on all

applicable sensors, whick are all disconnected now. We have good battery power to the

ecm connectors, have tested all grounds. I'm very hesistant to blame the ECM as they

are very dependable and very expensive. The only information I have is Mitchell On Demand. We cannot find a PCM on this truck , I'm assuming that this year (or half year)

model incorporates PCM functions thru the ECM. Hence my search for SAG as I've read

his posts for many years and know he's a dealer tech (and a good one). Any other

techs out there have ideas? TIA. . Tim Propes

Sorry, been on vacation in Florida with the wife. If you have power and ground to the ECM go ahead and cut the 5v wire(s) coming out of the ECM and measure the voltage on the ECM side of the wire. It sounds like the 5v is shorted somewhere in the harness if you have all the sensors disconnected.

There are up to five 5v circuits, connector 1 (C1) pin 27, DB/BR, C1 pin 42, VT/PK (A/T), BR/VT (M/T), C1 pin 54, PK/YL, C2 pin 23, YL/PK, C2 pin 33 VT/BR (MT).

Once you cut the 5v, try communicating again with the ECM. Make sure you leave enough room to solder and use quality shrink wrap.

 

[sag2]

Just as an FYI, the factory tools communicate with the ECM on the SCI BUS wires, the aftermarket tools and smog machines use the PCI BUS wires. The Cummins tool uses CCD BUS going to a dedicated 3 pin connector.

 

[TPro]

Thanks, SAG. I'll do this sometime today. I have a new FCM but i don't want to open the

box unless I know the ECM can communicate. Seafish, Cerberusiam and TCDiesel

stepped up in your absence and got me started in the right direction.

 

[TPro]

Today I cut the three wires on connector #1 and have 10volts on all three, coming out

of the ECM (battery voltage at 11. 87, key on, headlights on. While I was disconnecting

connector 2, I heard the fuel pump relay click and the a/c compressor clutch energize,

all with the key out of the ignition. I haven't cut the other wires in connector 2 cause

this is kinda spooky. I tested for data bus activity on the ALDL connector and have very

weak activity (less than . 30 volts) on the SCI wires, no activity on the PCI bus wire.

Should I go ahead and cut the two remaining wires or what? TIA

 

[sag2]

Might as well, that is why they make solder and shrink wrap. Just make sure you use good stuff. Sounds like you are onto something, probably a circuit shorted so I could continue on with the diagnosis. Get some alligator clip jumper wires and use them to temporarily reconnect the 5v circuits one at a time (get enough to do all of them) if cutting them gets your communication back.

 

[TPro]

I cut the remaining wire and now have no voltage at any of the five with key on. This is

with a new FCM installed. Sure looks like a bad ECM

 

[sag2]

OK, what is the "rest of the story"? What happened prior to this? Any repairs, modifications, parts replaced? Are you sure you load tested the powers and grounds? I use a halogen headlamp bulb. Before you replace it, if you can plug it into another 2003-2005 truck and see if you can communicate with it then. Don't attempt to start it, just turn the key to the run position and try to talk to it. The only thing to worry about is both trucks have to be equipped with SKIM keys, or both can not. If you mix a SKIM with a non SKIM one truck will not start again when you swap the ECM's back.

 

[TPro]

Well, we've put this on the back burner cause the a/c jobs are backed up. I've got the

vehicle for a while yet, so we'll do the ECM swap as soon as we get a chance. I need to

ask though, is it a sure fire indication that a vehicle is SKIM if it has the plastic halo

around the key? or do I need to look for a module somewhere?

Many thanks guys, I'm not giving up.

 

[sag2]

Regular key has a black thin head, SKIM key has a thick (1/4") gray head. Send the last 8 of the VIN and we can tell for sure.