Vehicles SPN 2003 Code Explained and Troubleshooting Posted by David T on August 2, 2022 Read Next → Vehicles SPN 4364 FMI 18 DTC Explained, Troubleshooting Vehicles SPN 4334 FMI [2-18] Troubleshooting Explained Vehicles SPN 3264 FMI [0-16] Troubleshooting Explained SPN 2003 is a diagnostic trouble code for bad connection between ECM and TCM. Troubleshoot: ECM, TCM wiring harness David T Read Next → Vehicles SPN 4364 FMI 18 DTC Explained, Troubleshooting Vehicles SPN 4334 FMI [2-18] Troubleshooting Explained Vehicles SPN 3264 FMI [0-16] Troubleshooting Explained