Diagnosing Intermittent Shutdowns on a DT466E Engine

[MikePhua]

The DT466E and Its Electronic Evolution
The DT466E is a turbocharged, electronically controlled diesel engine produced by Navistar International, widely used in medium-duty trucks, fire apparatus, and vocational vehicles from the mid-1990s through the early 2000s. It evolved from the mechanical DT466, a workhorse engine known for its wet-sleeve design and long service life. The “E” variant introduced electronic fuel injection via the HEUI (Hydraulic Electronic Unit Injector) system, integrating sensors, solenoids, and control modules to improve emissions and performance.
Navistar sold hundreds of thousands of DT466E engines globally, with many still in service today. Their reputation for durability is matched by occasional complexity in diagnostics, especially when electronic faults mimic mechanical failures.
Terminology Notes

• HEUI System: Uses high-pressure engine oil to actuate fuel injectors, controlled electronically by the ECM.
  
• ICP Sensor: Injection Control Pressure sensor, monitors oil pressure used to drive injectors.
  
• CMP Sensor: Camshaft Position sensor, provides timing input to the ECM.
  
• EEC / VPM / ICM: Electronic Engine Control, Vehicle Power Module, and Injection Control Module—three key control units in the DT466E system.
  

Symptoms and Initial Troubleshooting
In one case involving a 1997 fire truck with a DT466E, the engine would start and run smoothly in the bay, rev to full RPM, and idle indefinitely. However, under load or during driving, it would shut off abruptly—like flipping a switch—and emit a cloud of unburned fuel smoke. The truck would restart immediately and repeat the cycle.
Initial repairs included:

• Replacing the ICP sensor without improvement
  
• Replacing the fuel pump and seals
  
• Rebuilding injectors
  
• Replacing the CMP sensor, which resolved a no-start condition
  

Despite these efforts, the shutdown persisted with no diagnostic codes.
Electrical and Module Investigation
The absence of fault codes pointed to intermittent electrical failure. Technicians traced the issue to:

• Wiring Harness Faults: Movement or vibration caused signal loss. Wiggling connectors during operation sometimes triggered shutdowns.
  
• Relay Block on Firewall: Dirty or corroded 5-pin relays caused intermittent power loss. Cleaning or replacing relays restored function.
  
• Ground Connections: A small ground wire near the starter and battery was corroded. Cleaning and reseating improved stability.
  
• Battery Box Fuse Holders: Acid fumes caused corrosion, leading to voltage drops.
  

One operator noted a faint electrical smoke smell in the cab during early failures, prompting inspection of the EEC and VPM modules. No visible heat damage was found, but the possibility of internal failure remained.
Sensor Clearance and Installation Notes
The CMP sensor may require shimming for proper clearance. While some sensors are go/no-go, others benefit from precise depth alignment. In racing applications, crank sensors often have a clearance spec, and the same principle may apply here. Lack of shims on both old and new sensors raised questions about installation accuracy.
Preventive Measures and Recommendations

• Inspect and Clean Grounds: Especially small wires tied to main battery cables.
  
• Replace Relays Proactively: They are inexpensive and often the root cause.
  
• Check Harness Connectors: Wiggle test during operation can reveal faults.
  
• Use Dielectric Grease: Protects connectors from moisture and corrosion.
  
• Document Module Locations: EEC and VPM are often buried deep in the dash.
  

Conclusion
Intermittent shutdowns on a DT466E engine are often electrical in nature, not mechanical. While sensors and injectors may be replaced, the root cause frequently lies in wiring harnesses, relays, and ground paths. With methodical testing and attention to electrical integrity, operators can restore reliability to these engines. The DT466E remains a robust platform—when its electronic systems are properly maintained.