We do a lot of diagnosing at 441 Diesel but that’s not all we do. We do a lot of medium and heavy duty too. This particular truck is a 2005 Freightliner with a Detroit Diesel 60 series. The complaint was a consistent “check engine” light and no jake brake activation/no cruise. I checked it with the Detroit software and saw that the code was for an open circuit for the idle validation switch. The idle validation switch tells the ECM when the accelerator pedal is in the idle position. It is integrated into the accelerator pedal position switch which the previous shop had already replaced. The first thing I did was test the switch. The idle validation switch is just a 2 terminal switch that makes a circuit when the accelerator pedal is released and this completes the circuit sending a ground to the ECM indicating idle. After verifying the switch had 0 resistance when released and inf when pressed I knew the switch was good. The next step was testing the harness. I removed the connector at the ECM and checked continuity from ECM connector to IVS. The wire was definitely broken and showed infinite resistance. We removed the harness and took it apart.
After taking the harness apart we found this broken wire and 4 other wires that were eaten into. This part of the harness was at a sharp bend where a bracket held the harness. We decided to replace the entire vehicle harness because previous shops had done multiple repair to this harness and repinned the data link circuits. This repair shows where the disconnect is for many shops that do not understand wiring completely. If you have any electrical issues or have a truck that no one can fix leave it with 441 Diesel. Thanks guys