Glow plug control manages the electrical heating elements in diesel combustion chambers. The ECU controls pre-glow (before cranking), glow-during-start, and post-glow phases to ensure reliable ignition and reduce cold-start emissions.

Overview

Modern diesel engines use quick-start ceramic glow plugs that reach operating temperature in seconds. The ECU modulates glow plug current based on ambient and coolant temperature.

Controlled Signals

• Glow plug relay / PWM driver
• Glow plug current feedback
• Coolant temperature
• Ambient temperature
• Battery voltage

Maps Involved

• Pre-glow Duration Maps vs temperature
• Post-glow Duration Maps
• PWM Duty Cycle Maps
• Voltage Compensation Maps

Logic Sequence

Key-On → Temperature Check
         ↓
Pre-glow Duration Calculation
         ↓
Glow Indicator Light / Start Enable
         ↓
Cranking → Glow During Start
         ↓
Running → Post-glow Phase

Calibration Objectives

• Reliable cold start in all conditions
• Minimize white smoke at startup
• Optimize glow plug lifespan

Calibration Strategy

• Extend post-glow for cleaner cold idle
• Reduce pre-glow time if using high-performance plugs
• Verify start behavior across temperature range

Diagnostics

• Glow plug circuit faults (open/short)
• Hard cold start
• White smoke at idle

Best Practices

• Replace glow plugs as a set
• Check glow plug control module on older vehicles