Diff issue G500 - TC in Neutral ?!!!

I may be off on this, and I don't understand the connection, but in 463 autos, you get random TC errors when there is a battery/voltage issue.

I had such errors pop up on a G350 and replaced the main battery - no issues since.  I also bought a replacement small aux 12V battery, but never fitted that.  

Anyway, for a more informed diagnosis, try the following (It seems your garage is going in this direction):

The "TC in Neutral" warning on the dashboard of your 2005 Mercedes-Benz G500 (W463 chassis, left-hand drive) indicates that the vehicle's electronic control system detects the transfer case (TC) as being stuck or defaulting to neutral position, rather than the expected high-range (H) 4WD mode. This is often accompanied by the "LOW HIGH" prompt flashing or a blank/rectangle indicator where "H" or "L" should appear, and constant beeping (typically when the driver's door is opened with the ignition off and parking brake disengaged). The "Diff lock error" refers to the differential lock function being disabled or unresponsive—likely because the system locks out diff engagement as a safety measure when the TC position is unknown or neutral. This prevents accidental damage from mismatched gearing or loss of drive.

This is a very common issue in 2002–2005 G500 models (and early G55 AMGs), often due to the design of the electrically actuated transfer case. It's not typically related to the main transmission (722.6 automatic) or traction control (ESP/4-ETS) directly, but rather the TC's shift mechanism. Driving is usually still possible in high range, but you may notice:

• Slipping or whining/grinding noises from the TC during shifts.
• Inability to engage low range (L) or diff locks.
• Intermittent failures after parking, key-off cycles, or cold starts.

Root Causes

Based on extensive owner reports and service bulletins from Mercedes-Benz forums (e.g., ClubGwagen, Benzworld, MBWorld), the problem stems from:

1. Faulty Transfer Case Shift Motor (Servo): The electric motor that physically shifts the TC between high/neutral/low wears out or fails intermittently. The worm gear inside can strip, causing incomplete shifts. This is the most frequent culprit in pre-2006 models.
2. Outdated Transfer Case Control Module: Early modules (pre-2005) are prone to glitches in position sensing. Upgrading to a 2005+ module (part #A4635200160 or revised) improves reliability but doesn't always fully resolve it.
3. Adaptation/Calibration Loss: The system "learns" TC positions via sensors on the motor shaft. Wear, low battery voltage, or electrical glitches can cause it to forget, leading to false neutral readings.
4. Less Common: Low/dirty TC fluid (use MB 325.0 spec, ~1.3L), wiring faults, or parasitic battery drain (e.g., from the TC module keeping systems awake).

Mercedes issued a technical service bulletin (not a full recall) for 2002–2004 G500/G55 models, covering motor/module replacement under warranty. For 2005, it's often treated as a goodwill repair if mileage is reasonable, but expect out-of-pocket costs now (~$1,500–$3,000 for parts/labor at a dealer).

Immediate Fixes to Try

Before towing to a shop, attempt these reset procedures (safe to do with engine running; park on level ground):

1. Basic Reset (Most Common Success):
   • Start the engine.
   • Apply the parking brake firmly.
   • Shift the transmission to Neutral (N) using the gear selector.
   • Press and hold the "Low" (L) button on the center console for 10 seconds.
   • Release, then press and hold the "High" (H) button for 10 seconds.
   • Shift back to Park (P), turn off the engine, release the parking brake, and open the driver's door.
   • If the beeping stops and "H" appears on the dash, it's temporarily resolved. Drive 10–20 feet forward/backward to confirm engagement.
   Success rate: High for intermittent issues; repeats every few days/weeks if underlying fault persists.
2. Enhanced Rocking Reset (If Above Fails):
   • Engine running, transmission in Drive (D), slowly roll forward 6–12 inches.
   • Shift to Reverse (R), roll back 6–12 inches while lightly braking.
   • Repeat 2–3 times, then try the basic reset above.
   • This helps mechanically "nudge" the shift fork if it's slightly bound.
3. Battery Disconnect (Last Resort, DIY):
   • Disconnect the negative battery terminal for 10–15 minutes to reset modules.
   • Reconnect and perform the basic reset. Note: This may require radio/security code re-entry.

If these don't work or the vehicle won't move (rare, but possible with a full lockout), flatbed tow to a Mercedes specialist—avoid driving far, as TC slippage can cause overheating.

Recommended Next Steps

• Scan for Codes: Use an OBD-II scanner with Mercedes-specific support (e.g., iCarsoft MB V3.0 or dealer Star Diagnosis) to check for DTCs like P2260 (TC motor position sensor) or P2213 (TC malfunction). This pinpoints motor vs. module.
• Professional Repair:
  • Replace the TC shift motor (part #A4635200065, ~$800–$1,200) and perform adaptation via Star/Xentry (essential post-replacement).
  • Upgrade the control module if not already revised.
  • Flush/refill TC fluid during service.
• Prevention: Always engage parking brake before key-off to avoid false triggers. Use a battery tender if storing the vehicle. Regular 4WD use (e.g., monthly low-range test) keeps the system exercised.

This issue doesn't affect core engine/transmission safety but can strand you if it fully disengages drive. Many owners report 100k+ miles post-fix with no recurrence.

I have a couple of used ones for sale... not sure if you contacted me before when I had them on eBay

Gav