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Clayton, Mechanic
Category: Heavy Equipment
Satisfied Customers: 755
Experience:  5+ Years at Freightliner, Detroit & MBE Certified, ATD, and Electrical
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60 Series..quit on Tach as original.What..look next

Resolved Question:

FLD 120 60 Series DDEC lll
Tachometer quit working-Replaced-New one not working- Set codes on Tach as original.
What and where do I look next? Could it be a Sensor? How would I check that out?
What would the replacement Sensor # XXXXX?
Submitted: 4 years ago.
Category: Heavy Equipment
Expert:  Clayton replied 4 years ago.

Hi, Welcome to Just Answer, I am Clayton. I can help you with this.


What is the last 6 of the vin number?,


The tach is most likely driven off of the ECM, but I will look and make sure your truck is wired like this.


I have a wiring diagram I can look at so you can ohm out the wires from the tach to the ECM if it is wired this way.



Customer: replied 4 years ago.


VIN #838265 Freightliner FLD 120

Could you send wiring diagram so i can follow sequence

Thank you,



Expert:  Clayton replied 4 years ago.
On the Vehicle interface harness connector,(ECM, it will be Pin location #1, this harness connector is on the left side of the ECM, if you are facing the driver side of the engine.

This is circuit D505, this goes into a 2 pin connector. This 2 pin connector will be circuit d953, and d505.

The drawing I have is very generic.

Pull the panel for the tach down, look for these 2 circuits. Ohm Circuit 953 to ground, this should be the ground. Then Ohm the tach signal wire which is Circuit D505 to Pin 1 of the ECM connector. If you have good continuity here, then there is something going on with the switches in the tach, or the ECM's tach output is bad.

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