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The NAG1 is Chrysler's name for the Mercedes-Benz 722.6 five-speed automatic, also cataloged as the W5A580. Mercedes designed it; Chrysler licensed it and bolted it behind V6 and V8 rear-drive platforms after the Daimler-Chrysler era. You will find it in the 2005-up Jeep Grand Cherokee (WK) and Commander, the Dodge Charger, Challenger and Magnum, the Chrysler 300, the Dodge Durango, and various Ram applications, as well as in a huge range of Mercedes models under the 722.6 name. It is a durable, well-regarded transmission — when it is fed the correct fluid and its conductor plate is healthy.
The two things that get people in trouble on this unit are fluid choice and the fill procedure, because there is no dipstick and the fluid spec is not the ATF+4 many Mopar owners assume. Get both right and the service is straightforward. Get them wrong and you invite shudder, harsh shifts, or a comeback.
What a Fluid Change Costs (2026 US)
| Service | DIY Cost | Shop Cost |
|---|---|---|
| Drain & fill (pan drop, filter, gasket) | $90 - $180 | $250 - $450 |
| Full fluid exchange | $160 - $280 | $350 - $600 |
| Spec fluid (per quart) | $10 - $18/qt | included above |
| Filter, pan gasket & drain plug adapter kit | $40 - $90 | included above |
The spec fluid costs more per quart than a generic ATF, which is most of why this service runs higher than a domestic transmission. Many NAG1/722.6 pans integrate the filter into the pan itself, so the "filter" is often a filter-and-pan assembly — budget for that on higher-mileage units.
The Correct Fluid — Read This Before You Buy
The NAG1 / 722.6 calls for a fluid meeting the MB 236.14 approval (earlier builds referenced 236.12; 236.14 is the current-generation spec used for service). This is a specific Mercedes fluid standard. Do not assume this transmission takes ATF+4 just because it is in a Chrysler product — ATF+4 is the correct fluid for many other Mopar transmissions, but the NAG1 is a Mercedes design with its own approval. Using a non-approved fluid is a common cause of shudder and shift-quality complaints on this unit.
The rule: buy a fluid that explicitly carries the MB 236.14 approval (or is warranted by the maker to meet it). Confirm the approval on the bottle before you pour. If you are unsure whether your application spec'd ATF+4 or the MB fluid, verify against your build sheet or a dealer parts lookup rather than guessing.
| Spec | Detail |
|---|---|
| Fluid approval | MB 236.14 (Mercedes spec; 236.12 on early units) |
| Drain & fill (pan only) | roughly 5 quarts |
| Total capacity (dry, with converter) | roughly 9-10 quarts |
| Filter | often integrated into the pan assembly |
| Level check | no dipstick; set through fill/overflow at specified temperature |
Shop MB 236.14 spec ATF
Shop 722.6 / NAG1 filter & pan kits
Shop fluid fill pumps
Drain-and-Fill Procedure (No Dipstick)
Like the Mercedes original, the NAG1 is filled from underneath and level-set through an overflow tube at a controlled temperature. There is no dipstick and no top-side fill on most applications. The general sequence:
- With the vehicle level and cold, remove the drain plug and let the pan drain, then drop the pan (or filter-pan assembly) and replace the filter and gasket.
- Reinstall the pan with a new gasket. Many builds use a plastic overflow/fill tube inside — do not damage it.
- Refill through the fill port with your measured spec fluid using a pump, adding slightly more than you drained to account for what stays in the passages.
- Start the engine, foot on the brake, cycle through the gear positions and back to Park, and let the fluid come up to the specified checking temperature (a scan tool reading transmission temp is strongly recommended).
- With the engine running at the correct temperature, remove the overflow/check plug. When fluid dribbles rather than pours, the level is right — reinstall the plug.
Overfilling or checking at the wrong temperature is the most common DIY mistake here, and it directly causes poor shift quality. If you cannot read transmission fluid temperature, have a shop set the final level or get a scan tool that displays it.
Shop scan tools that read trans temp
Service Interval
Change the fluid every 40,000 to 60,000 miles for normal driving, and sooner if you tow or drive hard (the Charger/Challenger and Grand Cherokee crowd know who they are). Many of these were sold as sealed "lifetime" units; that is a maintenance-cost decision, not an engineering reality. Fresh MB-spec fluid is the cheapest protection this transmission will ever get.
Common Issues to Watch For
Conductor Plate Failure (The Big One)
The 722.6 / NAG1 has an internal electronic conductor plate that carries the speed sensors and solenoid connections and passes signals out through a sealed connector. When it fails — and on higher-mileage units it is a known wear item — you get erratic shifting, a transmission stuck in a single gear (limp/limp-home mode), a no-start in some cases, or speedometer/shift oddities. The good news is the conductor plate is a serviceable part that can be replaced without a full rebuild, so a limp-mode NAG1 is not automatically a dead transmission. Always have it diagnosed before you assume the worst.
Limp Mode
Limp-home mode (typically locking you into one gear so you can drive gently to a shop) is the transmission protecting itself. It can be triggered by the conductor plate, a speed-sensor fault, low or wrong fluid, or an electrical issue. Because the causes range from a cheap sensor to a bigger repair, a proper scan-tool diagnosis is essential rather than throwing parts at it.
Valve Body / Shift Quality
Worn fluid and age can bring harsh or delayed shifts; a fluid and filter service plus an adaptation reset resolves a lot of complaints. Persistent issues after fresh fluid point toward the valve body or conductor plate.
Need a Conductor Plate, Filter, or Rebuild Parts?
From a simple filter-and-pan service to a conductor plate or valve body repair, our companion shop gearboxinsider.com stocks NAG1 / 722.6 service and rebuild components. Same-day ship before 2pm Eastern.
Shop Gearbox Insider →FAQ
Can I just use ATF+4 in my NAG1?
No, not as a substitute for the specified fluid. The NAG1 is the Mercedes 722.6 and calls for a fluid meeting the MB 236.14 approval. ATF+4 is correct for many other Mopar transmissions but not for this one — using it is a common cause of shudder and shift complaints. Confirm the approval on the bottle.
My transmission is stuck in one gear. Is it dead?
Not necessarily. Being locked into a single gear is limp-home mode, and on the NAG1 the most common cause is a failing conductor plate, which is a replaceable part. Get it scanned before authorizing a rebuild.
Why is there no dipstick?
Mercedes designed it as a sealed unit that is level-set through an overflow port at a controlled temperature. It is normal for this transmission; you fill from underneath with a pump and check at the right temp.
How much fluid for a pan service?
Plan on about 5 quarts of MB 236.14 fluid for a drain-and-fill, and buy an extra quart so you can complete the hot-temperature level check without running short.