Transmission Speed Sensors (NAG1 / 722.6)

Symptoms

• Check Engine or transmission warning light illuminates, often accompanied by the transmission entering limp-home mode [0]
• Fault codes P2207 (output stage fault, speed sensor group), P220A (speed sensor 2 and 3 signal comparison not plausible), or P220B (speed signal comparison fault) stored in the TCM [0]
• Abnormal or erratic speedometer reading — for example, a displayed speed wildly out of range — which may be traceable to a wheel speed sensor PID via ESP/ABS scan data [3]
• Transmission stuck in a single gear or refusing to upshift normally, consistent with TCM receiving invalid speed data [0]
• High-pitched whine related to engine speed, which the NAG1 service manual links to the transmission being in limp-home mode [1]

Causes

• The shift valve body (X106) is defective — both speed sensor 2 (X106b7) and speed sensor 3 (X106b5) are integral to the valve body assembly, so internal valve body failure is the primary hardware cause [0]
• Signal comparison between speed sensor 2 and speed sensor 3 is not plausible, indicating one or both sensors inside the valve body are sending out-of-range or mismatched data [0]
• An over-speed condition is detected by the TCM comparing speed sensor 2 and speed sensor 3 signals, pointing again to valve body (X106) defect [0]
• For wheel speed sensor faults showing up as implausible vehicle speed readings, the sensor may have worked loose from its bore, allowing an air gap large enough to corrupt the signal [3]
• Short circuit to ground on cable A4.2/34 to X106x1/4, or an open circuit on the same wiring, can cause related sensor and temperature/starter lock-out faults on the same valve body connector [0]

Diagnosis

• Connect a scan tool capable of reading Mercedes/Sprinter TCM fault codes and check specifically for P2207, P220A, or P220B; these codes directly identify speed sensor 2 (X106b7) and speed sensor 3 (X106b5) or the shift valve body (X106) as the source [0]
• While connected, monitor live speed sensor PIDs in the ESP/ABS module to check for wildly out-of-range speed values (e.g., 158 mph at rest), which can help distinguish a wheel speed sensor fault from an internal transmission sensor fault [3]
• Inspect wiring and connector at X106x1/4 (valve body connector) for a short circuit to ground or open circuit on cable A4.2/34, as wiring faults can mimic sensor failure [0]
• Check transmission fluid level — low fluid can produce limp-home mode and noises that overlap with sensor symptoms [1]
• For a suspected loose wheel speed sensor, try pressing the sensor fully into its bore; if the fault clears, reseat or replace the sensor [3]

Repair

Speed sensor 2 (X106b7) and speed sensor 3 (X106b5) are not individually replaceable field components — the official remedy for P2207, P220A, and P220B is replacement of the entire shift valve body (X106) [0]. This is a transmission valve body job requiring fluid drain, pan removal, and careful handling of the conductor plate and solenoid wiring; it falls into the diy_with_skill category. A loose or failed wheel speed sensor in the ABS/ESP ring is a simpler, separate repair [3].

Parts

Plain part names — affiliate links and pricing are coming in a later update.

• Shift valve body (X106) — complete assembly (OEM or remanufactured)
• Transmission oil pan gasket
• Transmission filter and filter o-ring
• NAG1/722.6-specification automatic transmission fluid

Related forum threads

• 14 ↳More electrical gremlins- this one bad.

From the manuals

• Mercedes fault-code reference

  "P2207 Output stage fault speed sensor group Note: In older service literature, speed sensor 2 (X106b7) is also referred to as Y 3/6n2 and speed sensor 3 (X106b5) is also referred lo as Y3/6n3 Shift valve body (X106) 1s defective. Speed sensor 2 {X106b7) and speed Replace shift valve body {X106). P220A sensor 3 (X106b5) signal comparison not plausible Note: In older service literature, speed sensor 2 {X106b 7) is also referred to as Y3/6n2 and speed sensor 3 {X106b5) is also referred to as Y3/6n3. The Complete Sprinter Fault Code ~uide -Powertrain Systems -- Automatic Transmission Fault Monitor"

• Transmission service manual

  "Inspect valve body for sticky/stuck valves. Repair as needed. If valve motion is free, replace shift pressure solenoid and line pressure solenoid and retest. 3. Damaged or misbuilt clutch.3. Remove, disassemble and repair transmission as needed. 21 - 528 AUTOMATIC TRANSMISSION NAG1 - SERVICE INFORMATIONLX CONDITIONPOSSIBLE CAUSESCORRECTION EMCC Shudder1. Transmission adaptation/ calibration. 1. Check for latest level TCM software. Perform the TCM adaptation procedure. (Refer to 8 - ELECTRICAL/ELECTRONIC CONTROL MODULES/ TRANSMISSION CONTROL MODULE - STANDARD PROCEDURE) 2. Fluid condition, cont"

• Transmission service manual

  "Valve body malfunction.4. Check for sticky/stuck 2-3 shift pressure valve or regulator valve. 5. K3 or B2 clutch damaged.5. Disassemble transmission, inspect for damaged K3 or B2 clutch. Repair as needed. Slips on 4-5 upshift1. Transmission adaptation/ calibration. 1. Check for latest level TCM software. Perform the TCM adaptation procedure. (Refer to 8 - ELECTRICAL/ELECTRONIC CONTROL MODULES/ TRANSMISSION CONTROL MODULE - STANDARD PROCEDURE) 2. Fluid level low.2. Check and adjust fluid level. (Refer to 21 - TRANSMISSION/ AUTOMATIC - NAG1/FILTER - STANDARD PROCEDURE) 3. Filter damaged or missi"

• Transmission service manual

  "Filter plugged.3. Check TC out pressure, if < 10psi, check for plugged filter. Replace if needed. 4. Filter damaged or missing, missing filter o-ring. 4. Check for damaged/missing filter or cut/missing o-ring. 5 Hydraulic system-Low/no line pressure. 5. Remove valve body. Inspect or sticky/stuck regulator valve. If valve motion is free, replace line pressure solenoid and retest. If condition still exists check for worn/damaged pump. Replace pump assembly if needed. LX AUTOMATIC TRANSMISSION NAG1 - SERVICE INFORMATION 21 - 527 CONDITIONPOSSIBLE CAUSESCORRECTION Shudder garage shift R-D or D-R 1"

• Workshop manual (2000–2003)

  "Mount Uniform Tire Sizes On The Front Axle. NO UPSHIFT 3-4, 4-5 AFTER FAST OFF (ACCELERATOR) 1. Upshift Prevention To Realize Dynamical Drivestyle. 1. Instruct Customer. NO UPSHIFT OF 1ST GEAR BELOW 5000 RPM 1. Gear Recognition Switch.1. Replace Gear Recognition Switch. NO UPSHIFT INTO 5TH GEAR WHEN FULL THROTTLE OR KICK DOWN ACTIVATION 1. The Upshift 4-5 At Full Throttle or Kick Down Never Occurs Until Reaching Cut Off Speed. Under These Conditions, The High Powered Vehicle Will Never Shift Into 5th Gear Below 250 km/h. 1. Instruct Customer. NO KICK DOWN SHIFTING 1. Accelerator Pedal Value <"

• Workshop manual (2004–2006)

  "Mount Uniform Tire Sizes On The Front Axle. NO UPSHIFT 3-4, 4-5 AFTER FAST OFF (ACCELERATOR) 1. Upshift Prevention To Realize Dynamical Drivestyle. 1. Instruct Customer. NO UPSHIFT OF 1ST GEAR BELOW 5000 RPM 1. Gear Recognition Switch.1. Replace Gear Recognition Switch. NO UPSHIFT INTO 5TH GEAR WHEN FULL THROTTLE OR KICK DOWN ACTIVATION 1. The Upshift 4-5 At Full Throttle or Kick Down Never Occurs Until Reaching Cut Off Speed. Under These Conditions, The High Powered Vehicle Will Never Shift Into 5th Gear Below 250 km/h. 1. Instruct Customer. NO KICK DOWN SHIFTING 1. Accelerator Pedal Value <"

Sources