NAG1 Transmission in Jeep Wranglers — Complete Guide

The NAG1's Origins

The NAG1 five-speed automatic transmission was used in JK Wranglers from 2012 to 2018 behind the 3.6L Pentastar. It was designed by Mercedes-Benz and is also known as the 722.6. This transmission was used in Mercedes cars and SUVs for many years and is known for its strength and durability. It is a significant upgrade over the 42RLE and handles the Pentastar's power well even with larger tires.

The NAG1 has a 3.59 first gear and 0.83 fifth gear overdrive. The gear spacing is tighter than the 42RLE, which keeps the engine in its power band better during acceleration. The transmission uses a sophisticated adaptive learning system that adjusts shift firmness and timing based on driving habits. This system can be reset to restore factory shift behavior if the transmission has learned bad habits from a previous driver.

Common Issues

The NAG1 is generally reliable, but it has a few known issues. The transmission control module can develop problems with the internal solder joints, causing erratic shifting or failure to shift. This is more common on early 2012 and 2013 models. Reprogramming or replacing the TCM typically fixes the issue. The valve body can accumulate debris from normal wear, which affects shift quality over time.

The NAG1 is sensitive to fluid level. The transmission has a specific fill procedure that requires the transmission to be at operating temperature and the fluid to be checked with the engine running. An incorrect fluid level — either too high or too low — causes shifting problems that can be mistaken for internal damage. Always check the fluid level following the factory procedure before diagnosing other issues.

Maintenance Requirements

The NAG1 uses ATF+4 fluid, the same as the 42RLE. The factory claims the fluid is lifetime, but this is not accurate for Wrangler use. Change the fluid and filter every 50,000 miles for normal driving and every 30,000 miles if you off-road or tow. The transmission has a reusable pan gasket and a spin-on external filter that is easy to replace.

The NAG1 transmission cooler lines run to the radiator. These lines can develop leaks at the crimped connections, especially in rust-prone areas. Check the lines periodically for signs of fluid seepage. The rubber hose sections at the radiator connections are a common failure point. If you see fluid on the lines, replace them with aftermarket steel braided lines for a permanent fix.

Bottom Line

The NAG1 is a solid transmission that serves the JK well. Change the fluid and filter every 50,000 miles, use ATF+4, and keep the fluid level correct. Watch the cooler lines for leaks and address any shifting issues by checking the fluid level and TCM before assuming internal damage. With proper care, the NAG1 will outlast the rest of the drivetrain.

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