Where Is Your Grid Heater Location? A Complete Guide by Engine

The Grid Heater: Your Diesel’s Cold-Start Assistant

Diesel engines are marvels of efficiency and torque, but their reliance on the heat generated by high compression for fuel ignition presents a unique challenge in cold weather. Unlike gasoline engines that use a spark plug, a diesel engine may struggle to reach the necessary temperature for combustion when the engine block and incoming air are cold. To overcome this, manufacturers employ cold-start aids, with the grid heater being a prominent solution, particularly in Cummins-powered trucks.

What is a Grid Heater and What Does It Do?

A grid heater, also known as an intake air heater (IAH), is a powerful electrical heating element strategically placed in the engine’s air intake system. Its primary function is to warm the air charge before it enters the cylinders. This pre-heated air significantly aids in the ignition of diesel fuel during cold starts, ensuring the engine fires up more quickly and runs smoothly in low temperatures.

Beyond the initial start, the grid heater often continues to cycle for a period as the engine warms up. This post-start operation serves a crucial secondary purpose: it helps to ensure more complete combustion, which reduces the amount of white smoke (unburned fuel) and unburned hydrocarbon emissions that are common during a cold diesel engine’s warm-up phase.¹ For many owners, this system is a critical component for reliable year-round operation, and understanding its function is the first step in proper diesel engine maintenance.

How It Works: The Electrical Pathway

The operation of a grid heater is a coordinated effort between sensors, the engine’s computer, and high-amperage electrical components. When a driver turns the ignition key to the “On” position, the Engine Control Module (ECM) or Powertrain Control Module (PCM) first assesses the ambient air and engine coolant temperatures.

If the temperature is below a predetermined threshold—for many Cummins models, this is around 66°F (about 19°C)—the ECM initiates the pre-heat cycle. It sends a signal to one or more heavy-duty relays, or solenoids.³ These relays function as powerful switches, closing a circuit that draws an immense amount of electrical current—often between 150 and 200 amps—directly from the vehicle’s batteries. This massive current flows to the grid heater’s resistive element, causing it to glow red-hot, much like a toaster element.

Air being drawn into the engine passes over this glowing grid, rapidly increasing in temperature. This pre-heating phase can last anywhere from a few seconds to over a minute, depending on how cold it is.⁶ During this time, the “Wait to Start” or “coil” light illuminates on the dashboard. When the light goes out, it signals that the intake air has reached an adequate temperature for starting, and the driver can crank the engine.²

Signs of a Healthy Grid Heater

For truck owners, a few simple observations can confirm the grid heater is working correctly without requiring any special tools. The most telling sign is a noticeable dip on the vehicle’s voltmeter when the “Wait to Start” light is on.³ This temporary voltage drop is a direct consequence of the massive 150-200 amp load the heater places on the electrical system. Headlights and dashboard lights may also dim momentarily as the grid cycles on and off.³

This visible electrical draw is not a symptom of a problem; rather, it is a clear confirmation that the relays are closing and that a high-current load is being successfully delivered to the heating element. In fact, the absence of this voltage dip on a cold day when the “Wait to Start” light is on can be the very first indication of a failure in the system, such as a faulty relay, a blown fusible link, or a burned-out heating element. Additionally, a distinct, audible “click” from under the hood often accompanies the start of the heating cycle, which is the sound of the large relays activating.¹⁰

Grid Heater Location: A Pinpoint Guide for Your Truck

The exact location of the grid heater or intake air heater varies significantly between different diesel engine manufacturers and even between different generations of the same engine. Knowing where to find it is essential for inspection, diagnosis, and maintenance.

Cummins (The Classic Grid Heater Engine)

Cummins engines are the most well-known users of the grid heater system as their primary cold-start aid.

5.9L Cummins Grid Heater Location (1998.5-2007)

On the popular 5.9L 24v Cummins engines, the grid heater is a distinct, rectangular plate. Its location is “sandwiched” directly between the intake air horn and the engine’s intake manifold, found on the driver’s side of the engine.² This modular design makes it a relatively straightforward component to access and replace.

6.7L Cummins Grid Heater Location (2007.5-2024)

With the introduction of the 6.7L engine, Cummins significantly changed the design. The grid heater is no longer a separate plate but is integrated directly into the cast aluminum intake manifold plenum cover.¹² This assembly is also located on the driver’s side of the engine, but it sits beneath the high-pressure fuel rail and injector lines.¹³ To access or replace it, a technician must first remove the intake horn, fuel rail, and all six injector lines, making the job considerably more involved.¹⁵

This fundamental design change from a separate component to an integrated one is directly linked to the system’s most notorious failure mode. While the 5.9L system was prone to primarily external electrical issues like faulty relays, the 6.7L’s integrated design placed the heater’s critical electrical fastening bolt and nut inside the intake plenum, directly above the intake runners. This seemingly minor packaging decision created the potential for a catastrophic mechanical failure, where a failed fastener could fall directly into a cylinder, a problem that would become widely known as the “killer bolt”.⁵

Powerstroke (Primarily Glow Plugs with an Auxiliary Heater)

Ford’s Powerstroke engines have historically taken a different approach to cold starting.

Finding the 7.3L Powerstroke Intake Air Heater (1999.5-2003)

The 7.3L Powerstroke relies on a robust glow plug system for its primary cold-start capability. However, models from 1999.5 to 2003 are also equipped with an auxiliary intake air heater. This heater is located on the driver’s side of the engine, threaded into the intake manifold’s “Y-bridge”.¹⁸ Its main purpose is not for starting but to reduce white smoke during prolonged idling periods in cold temperatures by keeping the intake air warm.¹⁸

Do Modern Powerstrokes (6.0L, 6.4L, 6.7L) Have a Grid Heater?

The answer is a definitive no. Modern Powerstroke engines, including the 6.0L, 6.4L, and 6.7L models, exclusively use a glow plug system for cold starting.² They do not have a factory-installed grid heater or an auxiliary intake air heater, which is a key architectural difference compared to the Cummins platform.²⁰

Duramax (Primarily Glow Plugs with an Auxiliary Heater)

Similar to Ford, GM’s Duramax engines primarily use glow plugs but have incorporated auxiliary intake air heaters on some models.

Locating the Intake Air Heater on LB7, LLY, LBZ, LMM, and LML Engines

On Duramax engines from the LB7 (2001) through the LML (2016), an intake air heater is located near the top of the intake manifold assembly.²² As with the 7.3L Powerstroke, this heater is an auxiliary system designed to aid in emissions control and reduce cold-start smoke, while glow plugs handle the primary task of getting the engine started.¹⁸ While its exact position can vary slightly by generation, it is generally accessible from the top of the engine.²⁴

Modern Duramax (L5P) and Cold-Start Systems

The modern L5P Duramax engine (2017 and newer) relies solely on an advanced and efficient glow plug system.² It does not use an auxiliary intake air heater, simplifying the intake tract and following the broader industry trend seen in modern Powerstroke engines.

Table: Grid Heater Location Quick Reference

Grid Heater vs. Glow Plugs: The Great Diesel Debate

The choice between a grid heater and glow plugs represents two different engineering philosophies for solving the same problem. Each has distinct advantages and disadvantages that have influenced manufacturer decisions for decades.

Head-to-Head Comparison: How They Differ

The fundamental difference lies in where the heating occurs.

• Glow Plugs: These are small, individual heating elements, with one installed in each cylinder. They thread directly into the combustion chamber or a pre-chamber and heat the air right at the point of combustion.²
• Grid Heaters: This is a single, large heating element located centrally in the intake manifold. It heats the entire volume of incoming air before it is distributed to the individual cylinders.¹

Table: Grid Heater vs. Glow Plugs: Pros & Cons

Why Ram & Cummins are Switching to Glow Plugs in 2025

In a landmark shift, Ram and Cummins announced that the 6.7L Cummins engine for the 2025 model year will no longer use a grid heater, adopting a glow plug system instead.¹⁷ According to Ram’s engineering team, this change was primarily driven by a broader engine redesign aimed at improving emissions and performance. A new bolt-on intake manifold and the relocation of other components made the integration of glow plugs a more efficient packaging solution.¹⁷ The most significant benefit touted for customers is a drastic reduction in cold-start wait times—down to as little as three seconds from over 30 seconds with the grid heater.²⁶

While these engineering and customer-experience reasons are valid, the long and troubled history of the 6.7L grid heater’s “killer bolt” failure undoubtedly played a major role in this strategic decision. For over a decade, the potential for a small, inexpensive part to cause a catastrophic, five-figure engine failure has been a significant stain on the engine’s otherwise stellar reputation for reliability.¹¹ This issue spawned a thriving aftermarket of “delete” and “fix” kits and created persistent concern among owners. By switching to glow plugs—a technology used reliably by competitors for decades—Ram and Cummins not only modernize their starting system but also decisively eliminate their most infamous and costly point of failure. This move simultaneously addresses engineering goals, improves the customer experience, and resolves a long-standing reliability concern.

Troubleshooting a Failing Grid Heater: Symptoms, Codes, and Tests

When a grid heater system begins to fail, it typically provides a series of warning signs. Recognizing these symptoms and understanding the associated trouble codes can help owners diagnose the problem before it leaves them stranded.

Common Symptoms of Failure

Owners should be alert for the following indicators of a malfunctioning grid heater system:

• Hard Starting or Extended Cranking in Cold Weather: This is the most direct symptom. The engine takes longer to fire up because the intake air is not being pre-heated.²
• Excessive White Smoke on Startup: The white smoke is essentially atomized, unburned diesel fuel exiting the exhaust. It’s a clear sign of poor initial combustion due to insufficient heat.¹⁰
• Rough Idle After a Cold Start: The engine may stumble, misfire, or run erratically for the first minute or two until the cylinders generate enough heat on their own to sustain smooth combustion.²
• No Voltmeter Dip or Dimming Lights: As noted earlier, the absence of the characteristic heavy electrical draw during a cold key-on cycle is a strong indicator that the heater is not receiving power.³

Decoding the Check Engine Light: Common Grid Heater DTCs

The ECM continuously monitors the grid heater circuit for proper voltage and performance. If it detects a fault, it will illuminate the Check Engine Light (CEL) and store a Diagnostic Trouble Code (DTC). Owners can access these codes by.

Table: Common Grid Heater Trouble Codes

How to Test Your Grid Heater System

For those comfortable with basic automotive diagnostics, testing the grid heater system is relatively straightforward.

• Testing the Relays/Solenoids: The simplest test is to have an assistant turn the key to the “on” position in cold weather while listening for the audible “click” of the relays engaging.¹⁰ To test more thoroughly, a multimeter or 12V test light is needed. Check for constant battery voltage at the relay’s main input stud. Then, check for voltage at the output stud that leads to the heater only during the pre-heat cycle. If there is power going in but not coming out when commanded, the relay is faulty.³⁰
• Testing the Heater Element: Disconnect the main power wire from the grid heater stud. Set a multimeter to the resistance (ohms) setting. Touch one probe to the heater stud and the other to a good engine ground. A functional heater should show very low resistance (continuity). An “OL” or infinite resistance reading indicates the heating element has burned out and is broken.¹⁰
• Testing the Complete Circuit: The most effective field test is to connect a test light to the main power stud on the grid heater itself and clip the other end to a ground. Have an assistant turn the key on. The test light should illuminate brightly for the duration of the “Wait to Start” light cycle. This single test confirms that the ECM, relays, and wiring are all working together to deliver power to the heater.³²

The “Killer Bolt”: A Critical Guide for 6.7L Cummins Owners

The term “killer bolt” refers to a specific and catastrophic failure mode unique to the grid heater in 2007.5-2024 Ram trucks with the 6.7L Cummins engine. This issue has been extensively documented by aftermarket companies like(https://bankspower.com/blogs/ram-tech-tips/history-of-ram-cummins-6-7l-grid-heater-failure) and is a serious concern for owners.¹¹

Understanding the Catastrophic Failure: What Happens and Why

The failure is a chain reaction. It often begins when the grid heater relay fails and sticks in the “on” position.²⁹ This sends a continuous, unregulated flow of over 200 amps to the heater element long after the engine has started. The element and its connections were never designed for continuous duty and begin to overheat severely.³³

This extreme heat, combined with engine vibration, causes the small bolt and nut securing the power connection on the underside of the intake plenum to fatigue, melt, or break off.⁵ Once free, the metal fragment falls into the intake manifold. Due to the manifold’s design and airflow dynamics, the debris is most likely to be ingested by cylinder #5 or #6. The result is immediate and catastrophic engine damage, including destroyed pistons, bent valves, and a damaged cylinder head, often requiring a complete engine replacement.²⁵

The “Jiggle Test”: A 30-Second Check That Could Save Your Engine

Fortunately, there is a simple, no-cost preventative check that every 6.7L Cummins owner should perform regularly. It is known as the “jiggle test.”

1. Ensure the engine is off and completely cool.
2. Locate the main power terminal for the grid heater on the driver’s side of the intake plenum. It is a stud with a large-gauge wire attached, secured by a nut.¹⁵
3. Gently but firmly grasp the terminal and attempt to wiggle it back and forth and side to side.³⁴

There should be absolutely zero movement. If the stud feels loose or has any perceptible play, it is a critical warning sign that the internal nut has loosened, and failure is imminent. The vehicle should not be operated until the grid heater assembly is inspected and repaired or replaced.¹⁵

Solutions and Prevention: Aftermarket Fixes and Upgrades

Owners concerned about this issue have several options:

• Upgraded Fastener Kits: Companies like BD Diesel offer a “Killer Grid Heater Upgrade Kit” that replaces the factory bolt and bus bar with a more robust design intended to better withstand the heat and vibration.¹⁵
• Relocated Heater Kits: Some aftermarket solutions, such as those from Glacier Diesel Power, provide a full replacement intake plate that deletes the factory heater, but include a new, safer heating element that is installed externally or in a different part of the intake tract.³³
• Full Intake System Upgrades: High-performance intake systems, like the Banks Monster-Ram, completely replace the restrictive factory plenum and integrated heater. They often replace it with a simple delete plate for maximum airflow or a redesigned, vertically mounted coil-style heater that eliminates the problematic bolt design entirely.¹¹

The Grid Heater Delete: Pros, Cons, and Considerations

A popular modification, especially for 6.7L Cummins owners, is to completely remove or “delete” the factory grid heater. This modification has significant benefits but also comes with serious drawbacks that every owner must consider.

Why Delete the Grid Heater?

There are two primary motivations for this modification:

1. Reliability: For 6.7L Cummins owners, the number one reason is to permanently eliminate the risk of the “killer bolt” failure. By removing the entire assembly, the point of failure is gone.⁵
2. Performance: The factory grid heater element creates a significant obstruction to airflow in the intake manifold. Removing it smooths the air path, which can increase airflow, improve throttle response, allow the turbo to spool faster, and help lower Exhaust Gas Temperatures (EGTs), which can be beneficial when improving diesel towing performance.⁵

The Downsides: Cold-Weather Starts and CELs

Deleting the grid heater is not without consequences:

• Cold-Start Difficulty: This is the most significant drawback. In climates where temperatures regularly fall below freezing (32°F / 0°C), and especially below 0°F (-18°C), the engine will be extremely difficult or impossible to start without the grid heater or another starting aid like a block heater.⁵
• Check Engine Lights (CELs): The ECM expects to see the grid heater in the circuit. Removing it will cause the computer to detect an open circuit and trigger a CEL, typically with code P2609.¹² Erasing this code permanently often requires custom ECU tuning.³⁷
• Emissions Compliance: The grid heater is considered part of the vehicle’s emissions control system. Removing it may be illegal in jurisdictions with strict emissions testing and could cause the vehicle to fail an inspection.⁵ Owners should always verify local regulations before performing such modifications.

Is a Grid Heater Delete Right for You?

The decision depends almost entirely on climate and vehicle use.

• For owners in warm climates where temperatures rarely approach freezing, a grid heater delete is a very practical modification that enhances reliability and performance with minimal downside.³⁷
• For owners in cold climates, a full delete is generally not recommended for a daily-driven vehicle. The loss of cold-start capability is a major issue. For these owners, an aftermarket solution that relocates or redesigns the heater is a much better option, providing both reliability and cold-weather functionality.⁵ A block heater becomes essential if a delete is performed in a colder region.

Frequently Asked Questions (FAQs)

Q1: Where is the grid heater located on a 5.9 Cummins?

A: On a 5.9L Cummins, the grid heater is a distinct plate located on the driver’s side of the engine, positioned between the intake horn and the intake manifold.10

Q2: Do all Powerstroke engines have a grid heater?

A: No. Only the 1999.5-2003 7.3L Powerstroke has an auxiliary intake air heater. All modern Powerstroke engines (6.0L, 6.4L, 6.7L) use glow plugs exclusively for cold starts.2

Q3: What is the “killer bolt” on a 6.7 Cummins?

A: The “killer bolt” refers to the fastener that holds the grid heater’s power connection inside the intake manifold on 2007.5-2024 6.7L Cummins engines. It is known to fail from overheating, fall into a cylinder, and cause catastrophic engine damage.5

Q4: Will deleting my grid heater hurt my engine?

A: The act of deleting the heater will not harm the engine; in fact, it can improve airflow. However, it will make the engine very difficult to start in cold weather and will likely cause a persistent Check Engine Light unless the ECM is reprogrammed.38

Q5: Can I test my grid heater myself?

A: Yes. Simple tests include watching your truck’s voltmeter for a dip during a cold key-on, listening for the relay’s “click,” or using a 12V test light on the heater’s main power stud. For 6.7L Cummins owners, performing the “jiggle test” on this power stud is a crucial and easy preventative check.3