manolumber Posted December 13, 2014 Share Posted December 13, 2014 Have a code for an open circuit on the DEF line heaters. I suspect it may be something simple like a blown fuse or a bad relay. I can find a schematic for the DEF system on the Mack website but it does not include a complete circuit for the line heaters. Checked the legend for the fuse panels and all I can find are main power feeds for the DEF module. I know there are fuses in the left lower fuse panel for the heated side of the NOX sensors. Is there a fuse for the DEF line heaters? Can someone post a complete schematic for the DEF line heaters? The truck in question is a 2012 CXU with catalyzed DPF. Thanks in advance! Quote Link to comment https://www.bigmacktrucks.com/topic/38087-2012-mp7-def-line-heater-issue/ Share on other sites More sharing options...
Macktech689 Posted December 13, 2014 Share Posted December 13, 2014 The DEF line heaters are controlled by the aftertreatment control module mounted on the left side of the DEF tank. There is an output for lines 1&3 and another output for line 2. Check the connectors for corrosion and the line resistance, sorry I'm not computer savvy enough to post the schematic. Quote Link to comment https://www.bigmacktrucks.com/topic/38087-2012-mp7-def-line-heater-issue/#findComment-270303 Share on other sites More sharing options...
manolumber Posted December 14, 2014 Author Share Posted December 14, 2014 Thanks Porch. Yes, my schematic shows the module and describes the line heater circuits as "outputs" but I was not sure if these outputs are actually voltage out from the module or if there is a fused voltage source which the module grounds. The schematic I have does not show the complete circuit, only the module outputs.Are the line heaters a resistant wrap which extends the length of the line or a heated "block" which is located at specific locations. Everything is thoroughly wrapped so instead of tearing into the whole of the wrapping I was hoping to locate the position of the heaters and connectors and both the source and ground side of the heater ciruits?. Thanks again Quote Link to comment https://www.bigmacktrucks.com/topic/38087-2012-mp7-def-line-heater-issue/#findComment-270379 Share on other sites More sharing options...
Macktech689 Posted December 14, 2014 Share Posted December 14, 2014 There is a 12V driver in the module that supplies voltage to the heater circuits, the module grounds the heaters when needed. The line heaters are part of the line assemblies, if a line heater is faulty the line needs to be replaced. The connectors for the line heaters are in the DEF harness behind the tank, keep in mind the connectors are not "BOZO" proof and can be hooked up incorrectly causing "open" faults. Quote Link to comment https://www.bigmacktrucks.com/topic/38087-2012-mp7-def-line-heater-issue/#findComment-270408 Share on other sites More sharing options...
manolumber Posted December 14, 2014 Author Share Posted December 14, 2014 Thanks again Porch, great info. So, I can ohm the heater circuits by disconnecting the harness at the module and using the harness pins in that connector because the circuity begins and ends at the module?. Ever any problems with the terminals/connectors at the module? Any idea what the ohm range should be? Obviously if the circuit is open it will be infinity but just curious?I should have mentioned this initially, sorry but I just remembered....when I went to the SCR diagnostics I activated the line heaters manually and showed "100%" reaction on each of the heater circuits. Does this mean the computer is seeing voltage on the return side of the heater circuits? If so, any other reason it would be setting these codes:spn 4354 fmi 5 spn 4356 fmi 5Thanks again for any advice! Quote Link to comment https://www.bigmacktrucks.com/topic/38087-2012-mp7-def-line-heater-issue/#findComment-270441 Share on other sites More sharing options...
Macktech689 Posted December 14, 2014 Share Posted December 14, 2014 If I saw those 2 faults logged the first thing I would check is the connectors, if the line connectors are hooked together and the harness connectors are hooked together thats wrong, the lines should be connected to the harness. You can check line resistance at the line connectors the ACM connector or the rectangular connector below the ACM connector,(FCUT in the schematic) can't remember the resistance in the heaters but if the lines are open there will be no continuity Quote Link to comment https://www.bigmacktrucks.com/topic/38087-2012-mp7-def-line-heater-issue/#findComment-270442 Share on other sites More sharing options...
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