Cylinder 4 Glow Plug Circuit
The engine control module has detected a malfunction in the glow plug circuit for cylinder #4. Glow plugs pre-heat the combustion chamber in diesel engines to facilitate cold starting. A failure in this circuit prevents proper heating of that cylinder.
What You Might Notice
- Check engine light illuminated
- Difficulty starting engine in cold weather
- Rough idle when engine first starts
- Excessive white smoke from exhaust during cold start
- Engine misfire on cylinder #4
Most Common Causes
- 1
Failed glow plug
The glow plug element in cylinder #4 has burned out or failed electrically. This is the most common cause and prevents that cylinder from being pre-heated.
- 2
Glow plug relay failure
The relay controlling power to the glow plug circuit has failed, cutting off voltage to the glow plugs during the preheat cycle.
- 3
Wiring or connector issues
Corroded connectors, broken wires, or loose connections in the glow plug circuit for cylinder #4 are preventing proper electrical flow.
- 4
Engine control module fault
The ECM itself may have a fault in the glow plug control circuit, though this is less common than component failures.
How to Diagnose It
- 1
Check Failed glow plug — The glow plug element in cylinder #4 has burned out or failed electrically. This is the most common cause and prevents that cylinder from being pre-heated.
- 2
Check Glow plug relay failure — The relay controlling power to the glow plug circuit has failed, cutting off voltage to the glow plugs during the preheat cycle.
- 3
Check Wiring or connector issues — Corroded connectors, broken wires, or loose connections in the glow plug circuit for cylinder #4 are preventing proper electrical flow.
- 4
Check Engine control module fault — The ECM itself may have a fault in the glow plug control circuit, though this is less common than component failures.
How to Fix It
- 1
Replace glow plug in cylinder #4
Remove the old glow plug and install a new one rated for your specific diesel engine. Torque to manufacturer specifications to avoid damage.
- 2
Inspect and repair glow plug wiring
Check the wiring harness and connectors leading to cylinder #4's glow plug for corrosion, damage, or loose connections. Repair or replace as needed and ensure proper contact.
- 3
Test and replace glow plug relay
Test the glow plug relay with a multimeter to verify it's functioning. If faulty, replace with an OEM or quality aftermarket relay to restore circuit power.
- 4
Check engine control module
If other components test good, have the ECM scanned with advanced diagnostics to verify it's sending proper control signals. ECM reprogramming or replacement may be necessary.
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