How to Test a 722.6 Valve Body Before You Replace It

Your Mercedes 722.6 (NAG1 on Chrysler, Jeep and Dodge applications) is shifting hard, flaring between gears, dropping into limp mode or sitting in second gear. The easy conclusion is "bad valve body." Sometimes that is right. Often the real fault is one solenoid, a worn bore that a small repair kit fixes, or the conductor plate and 13-pin case connector bolted on top of the valve body. Testing in the right order tells you which part to buy before you spend money on a whole valve body.

This guide walks through that order: codes and symptoms first, then solenoid resistance at the connector, then a visual check of the conductor plate, then vacuum testing the known wear bores with the valve body on the bench.

Step 1: Match the Symptom to the Likely Circuit

Different 722.6 faults produce different complaints. Write down exactly what the transmission does before you pull anything apart.

• Harsh shifts, slow downshifts, limp mode, stuck in second gear. YouCanic lists all four as symptoms of a failed conductor plate, the electrical board that carries the solenoids and speed sensors on top of the valve body.
• Flare, bump or harsh shifts, slipping. Sonnax ties these to wear at the 1-2/4-5, 2-3 and 3-4 overlap control valve sleeves, which lets modulating oil pressure exhaust.
• No 2-3 shift, 4-3 neutral, soft shifts under acceleration, slip codes, delayed engagement, no lockup. Sonnax ties this group to too much valve-to-bore clearance at the modulating pressure area of the pressure regulator valve, which lowers line pressure.

Scan the transmission control unit for stored codes before you do anything else. Solenoid and speed-sensor circuit codes point to the electrical side (Steps 2 and 3). Slip or ratio codes with a clean electrical side point to the hydraulic side (Step 4). For more on reading the symptoms, see our guide to 722.6 valve body symptoms.

Step 2: Ohm-Test the Solenoids at the Connector

You can check all six solenoids without dropping the pan. Unplug the harness from the 13-pin case connector (turn the bayonet lock counterclockwise and pull it out, per YouCanic) and measure resistance across the pins with a digital multimeter. The ATSG 722.6 manual gives these specs, measured at the TCM or case connector, with pin 6 as the common:

Spec source: ATSG 722.6 service manual, solenoid resistance chart.

How to read the results:

• One reading open or far out of spec. Most likely a failed solenoid or a broken trace on the conductor plate. Pull the pan and test that solenoid directly to tell the two apart.
• Several readings bad at once, or readings that change when you wiggle the connector. Look at the 13-pin connector and the conductor plate before you blame the valve body.
• All six in spec. The electrical side is probably fine. Move on to the hydraulic tests.

Step 3: Inspect the Case Connector and Conductor Plate

YouCanic calls out a leaking 13-pin connector as a common weak point on this transmission. Fluid wicking through the connector can reach the harness and the control unit. Check the plug for oil. If it is wet, replacing the connector (YouCanic lists part number 2035400253) is part of the repair no matter what else you find.

If the codes and ohm readings point to the conductor plate, it can be replaced without replacing the valve body. YouCanic lists conductor plate part numbers 1402701161, 1402700861, 1402700761 and 1402700561. Confirm the right one for your VIN. They note that replacement plates come pre-programmed and usually do not need coding, but you still clear codes and run the adaptation reset afterward.

Step 4: Bench and Vacuum-Test the Valve Body

If the electrical side checks out and the shift complaint is still there, the valve body comes out for a hydraulic check. The 722.6 valve body has a small number of known wear bores, and each one has a matching Sonnax repair kit and a vacuum test:

• Overlap control valve sleeves (1-2/4-5, 2-3, 3-4). Sonnax describes continuous plunger valve oscillation wearing these bores. Their fix is the Master Overlap Control Valve Sleeve Kit, 68942-05K.
• Pressure regulator valve, modulating pressure area. Wear at the inner spool section. The fix is the Oversized Pressure Regulator Valve Kit, 68942-07K, for units with the OE .512 in. diameter spool only.
• Other kitted areas on the Sonnax 722.6 layout. The regulating pressure control valve spring (68942-01), the TC lockup clutch regulator valve (68942-10K), the lubricating pressure control valve (68942-14K), the regulating valve pressure control valve (68942-17K), and on late-style units the TCC damper valve (68942-23K).

For both main kits, Sonnax gives the same pass/fail rule: vacuum the indicated port. If it will not hold the minimum in-Hg, or if you can see wear, the bore needs the kit. Our valve body vacuum test guide covers the setup. One or two failed bores usually means a repair kit. Many failed bores, a cracked casting or scored separator plate means a replacement valve body.

When you reinstall the valve body, YouCanic warns that the gear selector lever must engage the sliding tab on the side of the valve body. If it does not, the vehicle will not move in Drive or Reverse.

The Fix: Buy the Part the Test Points To

• A solenoid out of spec: replace the failed solenoid, or all six with a complete kit while the pan is down.
• Leaking connector or failed conductor plate: replace that part and keep the valve body.
• One or two failed vacuum bores: install the matching repair kit and correct the shift feel with a shift kit.
• Widespread bore wear or casting damage: replace the valve body. Browse our transmission valve bodies.

Replace While You Are In There

• Filter and pan gasket. Required any time the pan comes off. Per YouCanic, pan bolts are 8 Nm (71 in-lb) and the drain plug is 20 Nm with a new washer.
• 13-pin case connector. Cheap, and a known leak point.
• Shift kit. If the valve body is already on the bench, a 722.6 shift kit goes in during the same teardown.

Cost and Effort

The connector ohm test takes a multimeter and a few minutes, and it costs nothing if the solenoids pass. Inspecting the conductor plate and testing solenoids directly is a pan-drop job, so plan on a filter, gasket and fluid refill. Vacuum testing needs the valve body out and on a clean bench, with a vacuum pump and test plate, and is the most time-consuming step. Testing in this order keeps a single-solenoid fault from becoming a full valve body purchase. For the full failure picture, see 722.6 valve body common failure points.

Frequently Asked Questions

Can I test 722.6 solenoids without removing the pan?

Yes. Unplug the 13-pin case connector and measure each solenoid across its pin pair with pin 6 as the common. ATSG specs are 2.5 to 6.5 ohms for the shift, MPC and SPC solenoids and 2.0 to 4.0 ohms for the TCC solenoid. An out-of-spec reading at the connector still needs a direct check with the pan off, because the fault could be the conductor plate instead of the solenoid.

Why is my 722.6 stuck in second gear?

YouCanic lists staying in second gear, along with limp mode, as a conductor plate failure symptom. Scan for codes and ohm-test the connector before you suspect the valve body.

Does a failed vacuum test mean I need a new valve body?

Not always. Sonnax sells repair kits for specific 722.6 bores, including the overlap control sleeves and the pressure regulator valve. If only one or two bores fail, a kit can fix it. Replace the valve body when wear is widespread or the casting or separator plate is damaged.

Sources

• ATSG 722.6 Service Manual - Solenoid Resistance Chart
• YouCanic - Mercedes 722.6 5G Transmission Valve Body Conductor Plate Replacement
• Sonnax - Mercedes 722.6 Valve Body Layout
• Sonnax - 722.6 Master Overlap Control Valve Sleeve Kit 68942-05K
• Sonnax - 722.6 Oversized Pressure Regulator Valve Kit 68942-07K