I’m at a loss, this is what my 05 lr3 4.4 is doing every time I try to start it. When I turn the key I get nothing, no click, no hesitation, no nothing except all these lights. I try to run the codes and it says “no communication to ecm/pcm A” it’s been to the dealer and they couldn’t figure it out, I replaced the TCCM, the brake switch, it’s got a new battery that tested good, repaired a bunch of corroded wires in both floor rails, replaced the ECM, replaced every fuse and relay, replaced the brake light bulbs just in case, and even checked the plug in the left rear wheel well. Is there something I’m just not seeing. Any help would be appreciated !!!!!

upon further testing I have found an oddity the “high can” is measuring 40ohms while asleep and I thought it should read 60 when normal and 120 if there is a bad resistor, instead it is measuring as if there is an extra resistor???? Also while ignition is on I am getting 2.4v out of the 6pin and 2.2v out of the 14pin on the OBD port when I thought I was supposed to get 2.7 out of 6pin and 2.4 out of 14pin would this cause the loss of communication????

 

Has the CJB been messed with? Thats the large module behind the glove box that EVERYTHING plugs into. Also if the HVAC panel is shot/inop/not plugged in the truck will not turn over. When it come to the bus, no clue really. I dont mess with that sorta stuff.

 

The voltages you are getting on the can buss indicates it is shorted. You are correct, if all is good it should be 60 ohms as you read 40 ohms that indicates a problem also. The resistors reside in two places - firstly on the instrument panel and the other end is on the ABS module. If you disconnect the plug to the ABS module you should read 120 ohms.
Here is a diagram showing pin connections - having problems attaching files

 

Globetrotter448; Where did you get that diagram?

That is worth its weight in gold.

I am going to put that someplace for safe keeping (only to forget where, and have to ask for a new one later)


Jeff

 

Thank you, I truly appreciate that diagram and will check again with the abs module disconnected. The part that concerns me is that it seems as if I’m getting extra resistance somewhere as I’m reading 40ohms that tells me that there are three resistance points all at around 120 ohms. It makes sense to loose a resistor and jump to the reading of 120 from 60 but to gain a resistor and jump from 60 to 40 is confusing me to say the least.

 

I made it up when I was troubleshooting a problem I had and figured it was a handy all in one place info

 

The same would happen if two can buss wire are shorted together. Possibly need to check that wiring in the sill area again.

 

Ok, so after digging through endless amounts of wiring and constantly checking my 6/14 pins for correct voltage and ohm readings as I disconnected what feels like every plug/fuse/relay/sensor/and computer I think I found it !!!!!!

When I disconnected the gauge cluster itself my ohms are at 60 where they should be and my volts are at 2.7 and 2.3. I’m assuming this means that the cluster was the culprit and should fix the problem by replacing it. The other thing that happened when I disconnected the cluster is that when I put the ignition in the on position my locks all cycled and the hazards came on which didn’t happen while checking everything else.

I just want to know if this sounds correct Before I spend the $850 on a new cluster ????

 

Or should it be reading 120 ohms because one of the resistors resides in the cluster ????

 

If disconnecting cluster and you get 60 ohms you still have a problem as you should see 120 ohms with the ABS plugged in. It shows that you still have a shorted problem somewhere