Hi all,

My friend has a 2011 Fit with an odd quirk. The rear hatch will unlock via the power locking system (Either via key fob, or internal buttons) but it will not lock the same way. I popped the internal trunk plastics off and can lock it manually by manually moving the latch, and replicate that it will always unlock via the electronics, but never lock with them,

For the moment, I've disconnected the green and white plugs for the latch so it stays locked. However, it's the base model, so this is a pain in the butt as there's no keyhole on the rear door.

I snagged a cheap rear latch mechanism on Amazon thinking that it was the latch, but I tested it (just plugged into the wiring plugs) before installing and the new one displays the same issue so it's clearly a wiring problem.

Anyone have tips to get it working again? I'm visiting them from out of state so I've got minimal tools and no multimeter, so my diagnosis is limited to "Hmmm, I wonder if this works" type stuff.

Thanks!

 

Disclaimer: This may or may not be a suitable troubleshooting step...

There is a Service Manual in the sticky at the top of the page. It appears it just reverses polarity to turn the lock motor in opposite directions to lock/unlock. Depending on your level of comfort/knowledge, switching the pins should reverse your symptom if it is a wiring issue. You could also test with a 12V jump box and small jumper wires (momentary touches ONLY.)

EDIT: After further thought, if it has power and ground to unlock, it should have power and ground to lock. It just reverses the polarity. If both door switch and key don't work, would that indicate a logic problem? Or can a stuck key cause the same symptom? What about using the key inserted into the lock cylinder on the driver's door? Doesn't a double twist unlock all doors? Would it also lock all doors? Too many questions...

 

My 09 latch always gets stuck and is starting to rust away. The door lock actuator motor is probably going and in time it won't unlock it either.

 

So, it appears that there is something internally wrong with the old latch that makes the locking system think the rear hatch is not closed, and thus does not engage the lock. The car itself doesn't give any indication the rear hatch is open, but the locking system knows.

Having the new latch plugged in, with the latch closed via pen, outside the door does NOT work. It will unlock, but not lock. Same as the old latch.

However, with the new latch fully bolted in and installed it all works perfectly once the trunk is closed, so there's something inside the latch that must need to detect the presence of the locking bar being fully engaged before the signal to lock the latch is applied by the computer.

Thanks everyone. The tip about the polarity swapping on the same wires was really helpful. It didn't work in reverse with the wires cros-connected, which narrowed it down to just the latch, not a wiring or computer or.

 

It could be mechanical. My CRX won't let you lock the driver's door unless it's closed or the interior latch handle is pulled while flipping the lock toggle. Electrical is also possible: a diode on one of the lock motor's leads would let it unlock but not lock, then a switch shorts across the diode (allowing both lock and unlock) when the hatch is fully latched.

 

@Black2011Fit Glad my miscellaneous ramblings helped. I often say that the questions are sometimes more important than the answers.

I would think that if any door were unlatched that no door would lock with the key fob, so I had to do some testing. My car, 2010 Sport AT, will not attempt to lock any of the doors with the key fob if any door/hatch is open. But, if you use the Lock Button on the driver's door or insert the key in the driver's door, all doors/hatch will lock even with the hatch open. I'm guessing the Owner's Manual details this, but it was quicker for me to test directly. I always use the key fob after all doors/hatch are closed, so hadn't discovered this (nor had I needed to.) Seems like good info for potential future troubleshooting.

Mark

 

From the 2012 service manual:
The wiring diagram shows the tailgate lock actuator is wired in parallel with the right rear door lock actuator, meaning if the right rear door locks and unlocks normally, the MICU (aka BCM, which produces the forward or reverse polarity electrical signal to drive the actuator motors) is operating normally. In that case, the problem would lie somewhere after the splice in the wiring that lets the two actuators share the same drive-signal-wiring. I haven't looked at wiring harness routing, but I'll guess that's on the floor near the B-pillar.
The Tailgate Lock Actuator Test makes no mention of the gate being latched or unlatched during testing. It just says apply power one way to make it lock, the other way to make it unlock. If it doesn't do that, replace it.
Sounds to me like the actuator motor has a dead armature coil. When the actuator comes to rest after an unlock cycle, the commutator brushes land on the contact for that dead coil. Closing the hatch either jostles the motor enough contact the next coil, or puts tension on the lock mechanism such that it rotates to the next coil so it can complete the next lock/unlock cycle. Unless you're having a lot of trouble finding a replacement and/or a lot more time and skills than money, replacement is the solution.