The 6.6L Duramax diesel engine, found in Chevrolet and GMC trucks from 2006 to 2012, utilizes a sophisticated glow plug system to ensure reliable cold starts. At the heart of this system is the Duramax Glow Plug Module, a critical component responsible for managing and delivering power to each individual glow plug. This article provides a comprehensive overview of the Duramax glow plug module, covering its function, common issues, diagnostic procedures, and replacement steps.
Understanding the Duramax Glow Plug System
The Duramax 6.6L diesel engine employs eight glow plugs, with one dedicated to each cylinder. Unlike simpler systems, the Duramax utilizes a glow plug control module that individually powers each glow plug via a dedicated transistor. This advanced design allows for precise control over glow plug operation, managed by the engine control module (ECM). The ECM determines glow plug cycle times based on various factors, primarily ambient temperature and engine coolant temperature.
The primary function of the glow plug system is to preheat the combustion chamber. In cold conditions, diesel fuel may not ignite readily upon compression. Glow plugs provide the necessary heat to ensure proper and complete combustion during engine start-up, and may briefly remain active after the engine starts to ensure smooth running. This is particularly crucial in cold climates where starting a diesel engine can be challenging.
When the Duramax glow plug module or individual glow plugs malfunction, it can lead to hard starting, rough idling immediately after startup, excessive engine cranking, or even a no-start condition in cold weather. Addressing these issues promptly is essential to maintain engine reliability and performance.
Duramax Glow Plug Module Programming
For LBZ and later Duramax engine variants, the glow plug module plays an additional role in fuel injector management. Fuel injector flow rates are stored not only in the ECM but also within the memory of the glow plug module. This redundancy ensures that if ECM communication is disrupted, critical injector data can be retrieved from the module.
Programming a new Duramax glow plug module involves transferring this injector flow rate information from the ECM to the new module. This procedure requires a specialized scan tool, such as a GM Tech 2 or an equivalent professional-grade diagnostic device that supports this functionality. Proper programming is crucial for optimal engine performance and fuel efficiency after replacing the module.
Duramax Glow Plug Module Parts List
Identifying the correct Duramax glow plug module and glow plugs for your specific Duramax engine is crucial for proper repair. Below is a parts list outlining the appropriate components for different 6.6L Duramax models within the 2006-2012 range:
| Part Description | Part Number(s) | Remarks |
|---|---|---|
| LBZ glow plug controller (2006 – 2007) | GM 98041624 | — |
| LMM glow plug controller (2007 – 2010) | GM 98089571 | — |
| LML glow plug controller (2011 – 2012) | GM 12652111 | — |
| Glow plug (LBZ, LMM, LML) | ACDelco 9G | [1] |
[1] – Replaces ACDelco 61G, not compatible with 2004 – 2005 model year LLY.
It is important to note the specific model year and engine code when ordering parts to ensure compatibility. Using the correct glow plug module and glow plugs will guarantee proper system function and prevent potential issues.
Diagnosing Duramax Glow Plug Module Issues
Ignoring glow plug system faults, even minor ones, can lead to more significant problems. Over-cycling or continuous power supply to a faulty glow plug can cause the glow plug tip to swell. A swollen glow plug tip can be difficult to remove, increasing the risk of damage to the cylinder head if the tip breaks off inside the cylinder. Prompt diagnosis and repair are therefore recommended.
Faults within the glow plug system can stem from the glow plug controller, individual glow plugs, wiring harness issues, connector problems, or a combination of these. Common diagnostic trouble codes (DTCs) associated with the glow plug system include:
- P0671 (cylinder 1 glow plug fault)
- P0672 (cylinder 2 glow plug fault)
- P0673 (cylinder 3 glow plug fault)
- P0674 (cylinder 4 glow plug fault)
- P0675 (cylinder 5 glow plug fault)
- P0676 (cylinder 6 glow plug fault)
- P0677 (cylinder 7 glow plug fault)
- P0678 (cylinder 8 glow plug fault)
- P0380 (glow plug circuit “A” malfunction)
- P0382 (glow plug circuit “B” malfunction)
While DTCs are helpful, they are not always present. If experiencing cold start issues, a systematic approach to diagnostics is necessary. Individual cylinder DTCs (P0671-P0678) often indicate a failed glow plug, whereas codes referencing a bank or circuit (P0380, P0382) may point towards a glow plug controller or wiring harness issue.
Start troubleshooting with a thorough visual inspection. Examine the glow plug controller, glow plugs, and all associated wiring. Pay close attention to electrical connectors for corrosion or damage and inspect wiring for chafing or breaks. Access to the glow plugs and wiring is improved by removing the passenger and driver side inner fender liners.
Check for corrosion at the glow plug ring terminals, flange nuts, and the battery power supply wire to the module. Also, verify the torque of the glow plug flange nut (44 in-lbs). A loose or corroded connection can disrupt the entire system and trigger DTCs. Intermittent faults are frequently caused by chafed wires or poor connections.
Testing the Duramax Glow Plug System
Diagnostic tests can pinpoint the source of glow plug system problems. Two key tests are the glow plug resistance test and the glow plug module voltage test.
Glow Plug Resistance Test (Ohm Test)
This test quickly assesses the condition of individual glow plugs.
- Set a multimeter to the resistance (Ohm – Ω) setting.
- Probe the terminal at the top of the glow plug with one test lead.
- Connect the second test lead to a good ground (glow plug base or engine block).
A multimeter is used to perform a resistance test on a Duramax glow plug, checking for continuity and proper function.
The resistance reading for each glow plug should be less than 1 Ohm. A reading above 1 Ohm indicates a faulty glow plug requiring replacement. A new ACDelco 9G glow plug typically measures around 0.4 Ohms. Ensure the glow plugs are OFF during this test.
Glow Plug Module Test Procedure
To verify the functionality of the glow plug module, perform the following voltage checks:
- Confirm battery voltage is adequate. Low voltage can cause module malfunction.
- Disconnect the large gauge battery voltage supply wire from the glow plug module. Measure voltage between this wire and ground. Battery voltage should be present. If not, check for battery terminal issues or circuit breaks. Reconnect if voltage is present.
- With the preheat sequence active (wait-to-start light illuminated), measure voltage at the top terminal of each glow plug to ground.
If a single glow plug is not receiving power, inspect its wiring. If a bank of glow plugs or all glow plugs lack power, the glow plug module is likely faulty and may require replacement.
How to Replace the Duramax Glow Plug Module
Replacing the Duramax glow plug module is a straightforward process. Follow these steps for successful replacement:
- Disconnect Batteries: Disconnect both negative battery cables to ensure safety.
- Locate Module: The glow plug controller is located on the driver’s side of the turbocharger, near the firewall.
- Remove Power Connector: Detach the round power feed connector (left side of module) by pressing the ridged segments and pulling it straight out.
The power connector is detached from the Duramax glow plug module by pressing the ridged segments and pulling outwards.
- Remove Rectangular Connector: Release the slide lock on the rectangular glow plug connector by sliding it towards the driver’s side. Pull the connector off the module.
- Remove Module Bolts: Use a 10mm socket to remove the two bolts securing the glow plug controller.
- Remove Module: Lift the glow plug controller off its bracket.
The bracket is visible after the Duramax glow plug controller has been removed.
- Install New Module: Installation is the reverse of removal. Mount the new glow plug controller on the bracket and tighten the two bolts to 89 inch-pounds (in-lbs).
- Reconnect Connectors and Batteries: Reattach the rectangular and round connectors, and reconnect the negative battery cables.
Replacing the Duramax glow plug module can resolve various cold start issues related to the glow plug system. Always ensure correct part selection and follow proper procedures for a successful repair.
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