F150 Lost Signal to Tach/Multifunction Commandlink

[Sooo Shallow]

I have a pair of 2006 F150's that I have owned since new with very little trouble. Two weeks ago I lost signal to one of the tachs. It powers on but just has a dash.

I bought a new tach, assigned it to engine #2 as it should be, and still the dash.

I removed the pigtail cable from engine 1 tach and connected it to the rear bus panel where the engines plug in, same result. I changed the rear bus panel, same result.

It appears to me that either the engine has stopped sending signal or the line from the engine to the rear bus has failed. Either seem rather unusual to me.

Any help would be appreciated.

[fairdeal]

i'm not following all your troubleshooting steps, but no matter:

that you have twins, and one engine/tach still works fine, AND that you still have trouble with a new tach,

seems culprit can only be on Engine #2 :
ECU
harness wiring/connectors
Command Link pigtail wire/connectors between engine harness - rear hub

A "bad connection" seems more likely than a "bad ECU".

Although I have read a claim of a spontaneously occurring bad contact of a single pin in an ECU connector. (not for the CL output specifically)

You could swap the ECUs and see what happens...

[Sooo Shallow]

Thank you for the reply.

I eliminated the rear bus panel by replacing it and using a known good pigtail to the tach from the rear bus eliminating all components in between the dash and the rear bus.

So yes, either the ECU or the pigtail from the engine to the rear bus must be the issue. I was just looking for some suggestions. I had not considered swapping ecu's, but a great idea.

I have not looked into where the ECU is located. Is it much trouble to swap?

[fairdeal]

I have not looked into where the ECU is located. Is it much trouble to swap?

Suggest remove power to the engine;
remove the cover below for access
and be reasonably careful with your manipulations plugging/unplugging.

[pstephens46]

Port side of engine towards the top. Square box sort of thing

[Sooo Shallow]

Thank you Very much!

[Sooo Shallow]

I did some more testing this weekend and after switching ECU's as suggested, the problem switched as well. No matter what I do, I only get a dash on the display from what appears to be the bad ECU instead of a 0 as the good one reports before I start the motor.
Seems odd, but I do not know where else to look other than replacing the ECU