ECM Main Relay Circuit Open
What does DD-1485-5 mean?
The DD-1485-5 (Detroit Diesel DD Series) diesel fault code means: ECM Main Relay Circuit Open. This is a moderate severity code.
Common Symptoms
- Check Engine Light / Amber Warning Lamp illuminated
- Hard starting or extended crank
- Extended key-off ECM power-down time
Probable Causes (Ranked by Likelihood)
- Failed main relay Likely
- Harness break Possible
Step-by-Step Diagnostic Procedure
Swap main relay with a known-good identical unit.
Verify coil and contact continuity.
Frequently Asked Questions
What is Detroit Diesel fault code DD-1485-5?
Detroit Diesel fault DD-1485-5 (SPN 1485 FMI 5) indicates: ECM Main Relay Circuit Open. It is a moderate-severity fault and is commonly seen on DD13/DD15/DD16 engines in Freightliner and Western Star chassis.
Can I drive my Freightliner or Western Star with fault DD-1485-5?
It depends on severity. Critical and serious faults trigger derate or engine shutdown — do not continue driving. Moderate faults usually allow continued operation short-term but schedule repair to prevent cascading aftertreatment damage.
How much does it cost to fix Detroit Diesel fault DD-1485-5?
Typical repair cost is $500-$2,200. Sensor/harness fixes fall at the low end; turbo actuator, injector, aftertreatment component, or head gasket repairs fall at the high end. Detroit DDDL software and sometimes factory parameter reset are required for proper reset.