How do you tell if you have a LS3 or L99?

The quickest way to tell is to check the factory engine code on your vehicle’s RPO label or window sticker: LS3 or L99. In practice, LS3 is the high-performance version often paired with a manual transmission, while L99 is the 6.2-liter engine equipped with Active Fuel Management (AFM) and typically found with an automatic transmission.

Where to look for the engine code

Use these steps to verify the engine family from official documentation and factory labels. This is the most reliable method to distinguish LS3 from L99.

Before you begin, know that the engine code is usually printed on factory paperwork or labels such as the door jamb/RPO label and the dealership build sheet. If you have access to a GM VIN decoder or can pull the vehicle’s build data from GM, the engine code will be LS3 or L99 for the relevant 6.2L variants.

1. Check the door jamb label or the window sticker for the engine code. Look for a line that lists the RPO code as LS3 or L99, which directly identifies the engine family.


2. Review the vehicle’s build sheet or Monroney sticker if available. It typically lists the engine code in the RPO section, giving a definitive answer.


3. If you only have the VIN, use a GM VIN decoder or contact a dealer to pull the RPOs associated with that VIN. The engine code read there will be LS3 or L99 for the 6.2L variants in question.


4. Know the typical pairing: LS3 is the higher-performance 6.2L usually found with a manual transmission, while L99 is the same size engine configured for AFM and commonly paired with an automatic transmission. This helps confirm when you also know the car’s transmission.

Verifying the engine code via paperwork is the most reliable way to distinguish LS3 from L99. If you have the correct documentation, you can skip ahead to final confirmation.

Practical checks if paperwork isn’t available

If you can’t access the official labels or build sheets, these practical cues can help you infer the engine type. Remember, there are exceptions depending on model year and configuration, so use these as guiding clues rather than absolute proof.

• Transmission pairing: L99 is designed for automatic transmissions (such as a 6-speed auto) in Camaro SS and similar models. If your car is automatic, L99 is more likely; if it’s a manual, LS3 is more likely. This is a strong clue but not foolproof.


• AFM hardware: L99 engines include Active Fuel Management (cylinder deactivation). If you can confirm AFM hardware or a software/ECU setting that enables AFM, this strongly suggests L99. Some cars may show AFM indicators in the odometer readout or scan tool.


• Engine block stamping: In some cases, the engine block may have a stamped code near the timing cover or other visible areas that identifies the engine family as LS3 or L99. Accessing the stamp might require removing a cover or view from the passenger side; not always easily visible.


• Official horsepower and option data: If you know the car’s original window sticker or spec sheet, LS3 versions typically show higher performance figures than the AFM-enabled L99. This can help corroborate the engine family when combined with other clues.

These practical checks can help when documentation isn’t handy, but they are best used alongside any available official data to reach a confident conclusion.

Summary

In short, the LS3 and L99 are both 6.2L V8s, but the key differences are AFM and transmission pairing. Check the engine code on the door jamb label or window sticker (RPO LS3 vs L99) for a definitive answer. If paperwork isn’t accessible, look at the transmission type (LS3 more common with manual; L99 with automatic) and search for AFM indicators or engine stamps as corroborating clues. When possible, verify with a GM VIN decoder or a dealer to be certain.

How do I know if I have a LS3 or L99?

The easiest way to tell the difference is to check the 8th digit of the VIN code. Follow this link to Identify an LS Engine by VIN.

How do I tell if I have an LS3?

You can identify an LS3 engine by checking the casting number on the block (e.g., 12621766) or by visual cues like the electronic throttle body, sensor on the timing cover, and its 6.2L (376 c.i.d.) displacement. It is a Gen 4 engine, so it will have the knock sensors on the sides of the block and the cam sensor on the front timing cover. 
Key identification methods 
This video explains the key differences between different LS engines, including the LS3: 57sPals Ocala Auto RepairYouTube · Aug 19, 2022

• Casting Number: Look for the casting number on the engine block, typically on the passenger side near the rear. The common LS3 casting numbers are 12621766 or 12623967. 
• Displacement: The LS3 is a 6.2L (376 c.i.d.) engine. You may be able to find a displacement stamp on the block, though its location can vary. 
• Throttle Body: The LS3 uses an electronic throttle body, not a cable-actuated one. This is a hallmark of Gen 4 LS engines. 
• Timing Cover: Gen 4 engines like the LS3 have a sensor on the front timing cover. A plain timing cover is characteristic of an older Gen 3 engine. 
• Engine Block Material: The LS3 has an aluminum block, which will not be attracted to a magnet. Truck engines could have either iron or aluminum blocks. 
• Knock Sensors: Gen 4 LS engines have the knock sensors on the sides of the block, whereas Gen 3 engines have them in the valley. 
• Cam Sensor: The cam sensor on a Gen 4 engine is located in the front timing cover. On Gen 3 engines, it's at the back of the valley. 
• VIN: If the engine is still in the vehicle, the 8th digit of the VIN can identify the engine. For the LS3, this digit is typically a "W". 

You can watch this video to learn how to identify LS engine generations: 49sSummit RacingYouTube · Jun 17, 2014

How do I know what engine is in my Camaro?

The 8th digit in a 4th gen Camaro's VIN is the engine code

1. S= 3.4L V6 (the L32 for '93-'95)
2. K= 3.8L V6 (the L36 for '95-'02)
3. P= 5.7L V8 (the LT1 for '93-'97)
4. G= 5.7L V8 (the LS1 for '98-'02)
5. 1993 = P.
6. 1994 = R.
7. 1995 = S.
8. 1996 = T.

How to identify LS3 engine?

You can identify an LS3 engine by looking for a casting number, checking for a 6.2L displacement, or by its specific visual features like rectangle-port cylinder heads and an electronic throttle body. Other identifiers include the VIN (if it's from an original vehicle), the engine's specific RPO code (if available), and its features like the composite intake manifold.
 
By casting number

• The most reliable method is to check the casting number on the engine block.
• For an LS3, look for casting numbers such as 12621766 or 12623967. 

By displacement

• The LS3 is a 6.2L (376 cubic inch) engine.
• This larger displacement is a key identifier, a result of the 4.065-inch bore diameter. 

By visual features

• Cylinder Heads: The LS3 has rectangle-port cylinder heads, a feature shared with other high-performance LS engines, differentiating it from earlier "cathedral port" heads. 
• Throttle Body: The LS3 uses an electronic throttle body, which is a key indicator for this Gen IV engine compared to older cable-operated throttle bodies. 
• Intake Manifold: Look for a composite intake manifold, which is designed to be lighter and improve performance. 
• Crank Sensor: For Gen IV engines like the LS3, the crank sensor is gray and located at the rear of the engine, unlike the black sensor on Gen III engines. 

This video shows how to identify the generation of an LS engine: 1:00Coverman66YouTube · Mar 7, 2022
By VIN

• If the engine is still in its original vehicle, you can use the Vehicle Identification Number (VIN). 
• The eighth digit of the VIN corresponds to the specific engine model. You can look up the VIN digit in a table to confirm if it corresponds to an LS3.