4-6 Serious Moderate DIY

LiftMaster Garage Door Opener 4-6 — Door lock engaged or wall-mount cable tension fault

LiftMaster Garage Door Opener · Error code 4-6

What 4-6 Means

On wall-mount jackshaft openers (8500, 8500W, 8500C), the cable tension monitor or door lock circuit reports a fault. The opener will not run until the lock or cable issue clears.

Symptoms

  • Wall-mount opener clicks but does not move door
  • Up arrow blinks 4, down arrow blinks 6
  • Manual lock indicator stuck
  • Cable tension monitor (CTM) LED red or flashing

Common Causes

1
Door lock pin engaged

Optional manual deadbolt on the door rail is engaged.

2
Cable tension monitor tripped

Lift cable went slack — door obstruction, broken spring, or off-track door.

3
CTM sensor failure

Microswitch in the cable tension monitor stuck.

4
Door lock relay/solenoid stuck

Automatic door lock accessory failed in locked state.

How to Fix It

  1. Check the door lock — disengage any manual lock pin or accessory automatic lock.
  2. Inspect both lift cables — if slack, the door is off track or a spring has failed; DO NOT operate opener.
  3. Verify door is fully closed and seated — manually lift to confirm balance.
  4. Inspect the cable tension monitor pulley/spring at the side of the door; reset per manual.
  5. If automatic lock 841LM is installed, remove it and retry to isolate.
  6. Replace failed CTM or lock accessory if isolation confirms.
  7. On confirmed broken spring or off-track door, call a garage door pro.

Parts You May Need

If diagnosis points to a failed part, these are the common replacements. As an Amazon Associate we earn from qualifying purchases.

Common replacement LiftMaster automatic deadbolt 841LM View on Amazon→ Common replacement Cable tension monitor parts kit View on Amazon→

More LiftMaster Garage Door Opener Codes

1-1 1-1 — Safety sensor wire short or reversed 1-2 1-2 — Safety sensor wire shorted or reversed 1-3 1-3 — Door control or wire issue 1-4 1-4 — Safety sensors misaligned 1-5 1-5 — Motor overheated or stuck 1-6 1-6 — Logic board or motor relay failure

All LiftMaster codes → All garage door opener codes →

Verified against manufacturer documentation: liftmaster.com

Always unplug an appliance before servicing it. This guide is for informational purposes and is not a substitute for a qualified technician.