3406e ecm no communication with ET

Hey hef I'm in lil over my head as usually...
D400e series 2 8ps800 ecm is not communicating with monitoring or prowertrain ecm or et I got 25v switched and unswitched and 10ohms on ground pins 4 5 6 plug one. But she's not totally dead dig sens pwr it +8v and sensor feed is +5v when key is on it pegs coolant temp gauge and I get .8vs on plug two pin 15 return. I'm thinking I have a communication issue. Does that sound right? Thanks hef

Comm problems can be tricky to chase down. There's a couple of strategies you can use. You could try;

• Unplugging the other ECMs in turn and see if you get communication with the engine
• Now you have them all unplugged, ohm out the CDL wiring between each module
• Make up a breakout harness and wire the comm adapter directly to the engine ECM CDL pins
• If you suspect the ECM, before condemning it, as a last resort I would remove it and power it up on the bench. Note that usually, you will only need 1 x bat +, 1 x ign +, and 1 x gnd to power it, but I would give powers and grounds to all the pins that need it, just to be sure to be sure.

Thanks cmark I left ecm in place tested harness out was getting pretty confident in bad ecm go to take it off and was previously mounted with wrong hardware wedging bolt into case. With it loose I had communication!!! I quickly did copy configuration. Here's the weird part it comes and goes I'm not super happy with the sockets in wiring harness for the twisted data link. So I'm going to put new ends on and new mounts and bolts try that but it almost feels like something might be loose inside ecm..... If I wiggle wires and ecm it will communicate and start but then I'll use in under a minute. It ran fine when parked just wouldn't start next shift.

Just a suggestion, in on-road 3406E back in late 90s it was common to find leads broken inside insulation at ECM connectors. We would take out each pin and perform a tug test on each, about 10 pounds of effort is all it takes. The seal that fits tightly into the connector body squeezes the wires where any vibration will contribute to breaks in the wiring, wire looks fine from outside, tug on it a bit and the wire stretches because the internal conductor is already broken.

I'll give it a go it's weird I was really working the harness testing it out and never communicated but once I loosened up ecm mounts then if worked for sort time periods. Kinda thinking for $600ish bucks should have ordered a harness.... The other odd thing is when it acts up I get one code from monitoring ecm saying it don't see engine but trans has no codes. If I have harness unhooked from engine ecm the trans shows 2 codes about engine ecm. Thanks for the insight been on some hair pulling out jobs lately.

Another thing from on-road , 2 fuse holders near starter. Terminals loosen up and fuse spaces get crusty. Just more to consider.

Get the ECM off the truck and build a bypass harness so you can test it on your bench...?
If you can communicate with it under those circumstances then it points the finger firmly at machine harness/wiring.
Below is a diagram for what works/worked on a 3408/3412 with an ADEM-II ECM. Batt + connects to BOTH Pins 6 and 23, Pin 6 to supply battery power to the ECM & the Comms Adapter, Pin 23 to simulate the machine key switch being in the ON position.
Your ECM may need the wiring connected to different Pin Numbers on the ECM (left) side, but the Comms Adapter (right side) will be good because they all connect the same way. A 12v motorcycle battery will give you enough power to run the Comms Adapter and power up the ECM.
I would say that the wires for the ATA Datalink would not be required unless you connect via ATA on this particular engine installation.



Edit: I looked at the Schematic (SENR9146) for 8PS800. You need Batt+ on Pins 4 & 6 of Connector #1 of the ECM. The Batt- (Pin 5) and the Cat Datalink connections (Pins 3 & 9) are the same. I don't see any additional grounds anywhere, other than the usual cable from the ECM "box" itself to one of the mounting bolts.

Have you tested for a communication signal with an oscilloscope? I don't know what protocol Cat uses, possibly TTL or CAN. Either way, a scope is the best way to check for communication. You have to be a little careful with terminating resistors, but you should be able to isolate which components are talking and which are not with a scope and some methodical probing and unplugging.

Here's a snip of the ECM connector. Wire #150 Orange on Pin #6 is only powered when the machine key switch is on, but you need Batt+ on both it and Pin #4 (Unswitched Power) to get the ECM to communicate.

Sorry for delay busy week.
After changing ecm mounts and important ecm harness pins ( really wasn't nothing wrong with old ones ) she ran for 2 days no issues then quit.
I took ecm to local dealer they flashed new one and verified old was bad. I gave tech my copy configuration from truck and so far so good it runs. I did do timing calibration. Thanks for all the input I sure learned alot about these older ecms. I will be making my own test harness but I learned I can only change parameters I can't do flash files.

Yep, only dealer versions of ET have Winflash which you need to upload software to ECMs.