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The W5A580 is a Mercedes-Benz 5-speed automatic (Mercedes internal code 722.6) that Chrysler licensed and badged the NAG1 ("New Automatic Gearbox, generation 1"). You will find it behind the Hemi and V6 in the Chrysler 300, Dodge Charger and Challenger, Magnum, Grand Cherokee (WK/WK2), Commander, Durango, and the JK Wrangler, as well as countless rear-drive Mercedes models. It is a fundamentally strong transmission. When it acts up, the cause is usually one of a short list of known weak points, and several of them are bolt-in fixes that do not require pulling the unit.
The single most important thing to know: on a NAG1, do not condemn the whole transmission before you have checked the conductor plate and the fluid. A huge share of "my transmission is dying" complaints on these are a $150 electronics part, not a rebuild.
The Conductor Plate — Failure Number One
The conductor plate is the internal electronic module that carries the speed sensors, solenoid wiring, and the transmission range signal, all in one plate bolted inside the valve body area. It is the NAG1's most common failure by a wide margin. When it degrades, the transmission commonly:
- Drops into limp mode (locked in a single gear, usually 2nd or 3rd) with no warning.
- Throws speed-sensor and range-sensor codes such as P0715, P0720, P0731-P0736, and gear-ratio-error codes.
- Shows a "gear indicator" that no longer matches the shifter, or a flashing gear display.
- Fails intermittently when hot, then works again after cooling — the classic sign of a heat-sensitive conductor plate.
The good news: the conductor plate is replaceable from underneath by dropping the pan, with the transmission still in the car. Many NAG1 conductor plates also carry a temperature sensor; buy the correct plate for your year and always replace the pan gasket and the plug/connector seal at the same time.
Shop NAG1 / W5A580 conductor plates
Valve Body & Harsh-Shift Problems
If the conductor plate checks out but the unit shifts harshly, bangs into gear, or flares between shifts, the valve body is the next suspect. On high-mileage NAG1s the valve body bores wear and the solenoids get sluggish, causing delayed engagement (especially a hard 1-2 or a clunk into reverse) and inconsistent shift quality. A related, cheaper culprit is the connector sleeve / 13-pin adapter plug where the external harness meets the transmission; it leaks fluid up the harness and causes electrical gremlins that mimic valve-body faults.
Order of attack when shifts are harsh: verify fluid level and condition, replace the conductor plate if suspect, replace the connector sleeve/adapter and its seals, then rebuild or replace the valve body if the problem remains. Jumping straight to a valve body without ruling out the plate and the connector wastes money.
W5A580 / 722.6 valve bodiesConnector adapter / 13-pin plug →
Other Common NAG1 Failures
- Torque converter lockup shudder. A shudder or vibration around 40-50 mph under light throttle is often the TCC clutch. Fresh correct fluid sometimes helps; a worn converter needs replacement.
- Overdrive (5th) clutch wear. High-mileage units can slip in top gear. This is an internal repair and usually points toward a rebuild.
- Limp mode from low or burnt fluid. The NAG1 is sensitive to fluid condition. Overheated or overdue fluid alone can trigger faults. Always confirm level and color first.
- Pan / connector leaks. A weeping pan gasket or the seeping 13-pin connector can drop the level enough to cause erratic behavior.
How to Diagnose It (Cheapest to Most Expensive)
- 1. Scan for codes. Read transmission codes with a scan tool that can access the TCM, not just generic engine codes. Speed/range/ratio codes point at the conductor plate.
- 2. Check fluid level and condition. Correct fluid, correct level, checked warm. Burnt-smelling or dark fluid changes the whole plan.
- 3. Note the failure pattern. Heat-sensitive intermittent limp = conductor plate. Consistent harsh engagement = valve body or connector. Speed-dependent shudder = converter. Slip only in 5th = internal clutch.
- 4. Fix in cost order. Conductor plate and connector first (both pan-off, in-car). Valve body next. Rebuild only if clutches are slipping or the diagnosis leads there.
Repair & Rebuild Cost Ranges
| Repair | DIY Parts | Shop Total |
|---|---|---|
| Conductor plate + pan gasket + fluid | ~$150-$300 | ~$400-$700 |
| Connector sleeve / 13-pin adapter | ~$40-$90 | ~$200-$400 |
| Valve body (reman) install | ~$300-$700 | ~$800-$1,400 |
| Torque converter replacement | ~$200-$450 part | ~$1,000-$1,700 |
| Full rebuild | ~$800-$1,500 kit | ~$2,500-$4,000 |
| Reman / replacement unit installed | — | ~$3,000-$5,000 |
The takeaway: the difference between a $500 fix and a $4,000 fix on a NAG1 usually comes down to whether the diagnosis started with the conductor plate or skipped it. Rule out the cheap electronic parts before anyone quotes you a rebuild.
Correct Fluid Spec
The W5A580 / 722.6 requires a fluid meeting the Mercedes-Benz 236.10 / 236.12 (later 236.14) specification. Note that standard Mopar ATF+4 is NOT the correct fluid for this unit despite it being a Chrysler-badged transmission. Use an ATF explicitly licensed to the MB 236.1x spec (often sold as "Mercedes 722.6 / NAG1 ATF"). Using the wrong fluid, including generic Dexron or ATF+4, causes shift-quality problems and can accelerate wear. Fluid capacity is roughly 5 quarts for a pan-drop service and around 9-10 quarts for a full fill. Replace the filter (it is integrated with many pan kits) and the pan gasket when you drop the pan.
Shop 722.6 / NAG1 (MB 236.14) ATFPan & filter kits →
NAG1 Parts, Ships Same-Day
Conductor plates, connector adapters, valve bodies, filters, and rebuild kits for the W5A580 / NAG1 — gearboxinsider.com stocks the parts a smart diagnosis actually needs. Same-day ship before 2pm Eastern.
Shop Gearbox Insider →FAQ
My NAG1 is stuck in one gear. Is it dead?
Probably not. Being locked in 2nd or 3rd is textbook limp mode, and on a NAG1 the most common cause is a failing conductor plate — a pan-off, in-car fix. Scan for speed/range codes before assuming a rebuild.
Can I replace the conductor plate myself?
Yes, if you can drop the transmission pan. It is bolted inside, connects to the external harness through the 13-pin connector, and comes out with the pan down. Replace the pan gasket and connector seal at the same time, and use the correct plate for your year.
What fluid does the W5A580 take?
An ATF meeting Mercedes-Benz spec 236.10/236.12/236.14 (sold as 722.6 / NAG1 fluid). Do not use generic Dexron or ATF+4. Wrong fluid causes shift problems on these units.
Is the NAG1 a reliable transmission overall?
Yes. The core 722.6 design is durable and high-mileage-capable. Its reputation for trouble comes almost entirely from the conductor plate and connector, both of which are inexpensive, known fixes when addressed early.