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 2017 Thomas B2 Cummins code 4156
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TRex
Senior Member

60 Posts

Posted - 07/08/2021 :  6:20:58 PM  Show Profile  Visit TRex's Homepage  Reply with Quote
4UZABRDT0HCHR7074 Freightliner/Thomas B2 Cummins ISB 6.7 CM 2350 ESN 73944784 Built 02-16 Have an active code 4156. “Aftertreatment 1 Diesel Exhaust Fluid Dosing Unit Heater Relay Circuit – Voltage Below Normal or Shorted to Low Source”. We are good thru the relay that is mounted near the firewall, drivers side, engine side. I do not have 12V at the DEF pump module. DEF unit is located on the pass. side frame near the step. Wiring goes from the DEF pump module into a 3’ bundle of wiring that goes over top of the trans and makes it way to the relay fuse blocks. . Looking for a possible known failure point in the wiring. TIA

Bluenozer
Advanced Member

Canada
441 Posts

Posted - 07/13/2021 :  02:14:29 AM  Show Profile  Reply with Quote
the fender mounted PDM i've seen issues with the power feed to PDM and the harness is bad from the PDM to frame rail, and the plug on frame that connects the ATF harness to ecm harness by turbo down pipe
pin 82 on ecm connector J2 is power supply

OEM trained in wiring and all engine platforms for 20 years

Edited by - Bluenozer on 07/13/2021 08:12:43 AM
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TRex
Senior Member

60 Posts

Posted - 07/14/2021 :  06:34:13 AM  Show Profile  Visit TRex's Homepage  Reply with Quote
Blue, we found this problem. Somebody poked a hole in the wire suplying the fuse and relay. Greenies got it. See that hole poking on quite a few buses from this fleet.
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