Cummins 3559 and 3558 fault codes often lead to unnecessary replacement of the DEF dosing unit. This comprehensive guide clarifies the root cause and provides troubleshooting steps for these codes, based on Cummins Inc. Technical Service Bulletin TSB190202.
Understanding Cummins 3559 and 3558 Fault Codes
These fault codes indicate an electrical issue within the OEM wiring harness of the DEF dosing unit, specifically a short or open circuit. Contrary to common practice, replacing the DEF dosing unit itself won’t resolve the problem as the fault lies within the wiring. The codes may manifest as active fault codes 3558 and/or 3559, potentially making the DEF dosing unit appear non-functional.
Root Cause of Cummins 3559 and 3558
The root cause is not a faulty DEF dosing unit, but rather a problem within the OEM wiring harness. This can include:
- Chafed wires: Wires rubbing against each other or other components, causing damage to the insulation.
- Damaged/exposed wires: Wires with cuts, breaks, or exposed conductors.
- Damaged pins: Bent, corroded, or broken pins in the connectors.
- Malfunctioning relay: A faulty relay can disrupt the electrical signal to the DEF dosing unit.
Troubleshooting Steps for Cummins 3559 and 3558
Before replacing any components, follow these diagnostic steps:
- Connect INSITE™: Use the INSITE™ electronic service tool to check for active fault codes.
- Prioritize Fault Codes 5865 and 5867: If these codes are present, troubleshoot them before addressing 3558 or 3559.
- Inspect Wiring Harness: Thoroughly examine the DEF dosing unit relay wiring harness for any signs of damage, including chafed wires, exposed wires, and damaged pins.
- Verify Relay Operation: Test the OEM aftertreatment DEF dosing unit relay to ensure proper functionality. A faulty relay can mimic the symptoms of codes 3558 and 3559.
- Check ECM Connection: Inspect the wire connecting the aftertreatment DEF dosing unit to ECM pin 79 for any damage.
- Consult OEM Resources: Refer to the OEM service information and troubleshooting documentation for detailed instructions specific to fault codes 3558 and 3559. This information will provide further guidance and diagrams to aid in diagnosis.
Conclusion
Cummins 3559 and 3558 fault codes point to wiring issues, not a faulty DEF dosing unit. Following the correct troubleshooting steps outlined in this guide and the Cummins TSB will save time and money by preventing unnecessary part replacements. Always consult official OEM documentation for comprehensive information and safety procedures. Accurate diagnosis and repair are crucial for maintaining the performance and longevity of your Cummins engine.
