The automatic door lock for the passenger side of my 2005 Corolla no longer works. I can't find out how to fix it. Is it simply an actuator, or is it something else?

Check for broke wires inside the boot from body to driver door , this is a common problem . If you don't find broke wire's , pull the door panel to get at driver door switch . Check for voltage an ground circuit .
Rendezvous Door Lock System Components
The power door lock system consists of the following components:
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Body control module (BCM)

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Driver door lock switch

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Front passenger door lock switch

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Door lock actuators in each of the doors

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Door lock system fuse into the BCM (BCM D 25A fuse)

Door Lock Operation
When the BCM detects a transition of either of the door lock switches to the LOCK position, it switches the door lock actuator lock control circuit to voltage. Since the lock actuator unlock control circuits are at ground potential within the BCM, the door lock actuator motors transition to the Lock position.
Driver Door Unlock Operation
When the BCM detects a transition of either of the door lock switches to the UNLOCK position, it switches the driver door lock actuator unlock control circuit to voltage. Since the door lock actuator lock control circuit is at ground potential within the BCM, the LF door lock actuator motor transitions to the Unlock position.
The driver door lock actuator unlock control circuit is a dedicated control circuit used only for the driver door lock actuator motor. This is done so that the driver door may be unlocked by itself using a keyless entry transmitter or an automatic door unlock function (if programmed).
Passenger Door Unlock Operation
When the BCM detects a transition of either of the door lock switches to the UNLOCK position, it switches the door lock actuator unlock control circuits to voltage. Since the door lock actuator lock control circuit is at ground potential within the BCM, the passenger door lock actuator motors transition to the Unlock position.
The door lock actuator unlock control circuits are dedicated control circuits used only for the passenger door lock actuator motors. This is done so that the driver door may be unlocked seperate from the passenger doors using a keyless entry transmitter or an automatic door unlock function (if programmed). This video on testing computer controlled door locks on a Subaru , doesn't matter . test yours same way > The BCM controls your door locks .
Are all of the power door locks inoperative from both door lock switches?

The locks on your vehicle are electronically controlled by the BCM - body control module . The driver an passenger door switche's are input's to the BCM . Do you know anything about automotive electronic's ? anti theft alarm remote, could this be part of the problem , No it's just a key less entry remote , nothing to do with the anti-theft .
Door Lock System Components
The Power Door Lock System consists of the following components:
• Body control module (BCM)
• Driver door lock switch
• Front passenger door lock switch
• Door lock actuators in each of the doors
• IBCM (PWR) 15-amp fuse

Door Lock System Controls
The Power Door Lock System is controlled by the body control module (BCM) and can be activated by any one of the following:
• A door lock switch Lock or Unlock actuation
• A keyless entry transmitter actuation
• An automatic door lock actuation
• An automatic door unlock actuation
• A last door closed locking (LDCL) actuation

Driver and Passenger Door Unlock Operation w/o Keyless Entry
When the body control module (BCM) detects a transition of either of the door lock switches to the Unlock position, it switches the door lock actuator unlock control circuits to voltage. Since the door lock actuator lock control circuit is at ground potential within the BCM, the driver passenger door lock actuators transition to the Unlock position.

Your best bet , take your vehicle to a qualified repair shop ! Need special tool to diagnose .

Power Door Locks Inoperative

Install a scan tool.
Turn ON the ignition, with the engine OFF.
With a scan tool, observe the door lock switch parameter in the Doors data list.
Does the scan tool display Idle?
YES - Go to Step 4
NO - Go to Step 8
4
Activate the driver door lock switch to the LOCK and UNLOCK positions.
Does the scan tool display Idle?
YES - Go to Step 9
NO - Go to Step 5
5
Activate the front passenger door lock switch to the LOCK and UNLOCK positions.
Does the scan tool display Idle?
YES - Go to Step 9
NO - Go to Step 6
6
With a scan tool, observe the driver door lock actuator command and the passenger door lock actuator command parameters in the Doors data list.
Activate a door lock switch to the LOCK and UNLOCK positions.

The power windows an power locks are controlled by a module , DDM - driver door module . As far as the locks locking when you put the vehicle into reverse an unlocking when you put the vehicle into park , that's how there are suppose to work , automatic lock an unlock feature . When you put the vehicle into any gear from park the locks should lock . Did she hit window lockout function ?

The power door lock system consists of the following components:
• The driver door module (DDM)
• The passenger door module (PDM)
• The body control module (BCM)
• The driver information center (DIC)
• The rear door lock switch
• The door lock relay
• The door unlock relay
• The liftgate lock relay--utility vehicles with liftgate only
• The reversible door lock actuators in each of the doors and liftgate
• LOCKS 20A fuse (rear lock/unlock relay supply voltage)
• ECC 10A fuse (liftgate lock relay supply voltage .

Programmable Automatic Door Locks
The automatic door lock feature can be programmed to control the door lock system. The automatic door lock feature is factory programmed to have all doors lock and unlock. For detailed instructions on programming the automatic door locks, refer to Vehicle Personalization in Personalization.
When the automatic door lock feature is programmed to control the door lock system, the driver door module (DDM), passenger door module (PDM) and body control module (BCM) will lock the vehicle doors if the following inputs are true:
• Ignition 1 input is active.
• All door jamb switch inputs are inactive.
• Cargo door or liftgate/liftglass ajar inputs are inactive.
• Transmission is shifted out of park.
This automatic door lock function will only occur once per ignition cycle unless, a door jamb switch input changes state to active and back to inactive. Then the DDM, PDM and BCM will lock all doors again.
Once the automatic door lock feature has locked the doors, the BCM will then unlock all the doors when the transmission is shifted into park.
Driver, Passenger and Cargo Door Lock System Operation
The front power door lock switches are integral components of the driver door module (DDM) and passenger door module (PDM). The switches are two position normally open rocker switches. When placed in either the lock or unlock positions, the switches provide a direct input to the DDM or PDM. The DDM or PDM monitors these inputs and sends a Class 2 message indicating a change in the switch's respective position. Modules which activate the power door lock motors receive the Class 2 message and activate the motor in the appropriate direction to lock or unlock the vehicle's doors and liftgate. The rear door lock switch provides a lock and unlock signal to the body control module (BCM). The BCM upon receipt of a lock or unlock signal will control the rear door lock relays and also send a Class 2 message to the DDM and PDM to perform the appropriate function.
The modules which activate the power lock motors are:
• The DDM (driver door lock actuator).
• The PDM (passenger front door lock actuator).
• The BCM (both rear door lock actuators and cargo door/liftgate).
The DDM and PDM are directly connected to the respective door lock actuator through the door lock motor lock and unlock circuits. Once a door lock or unlock request has been received, the module will supply battery voltage to one side of the actuator and ground the other causing the doors to lock or unlock.
The rear passenger and cargo doors differ slightly in that they use lock and unlock relays. The relays supply and coil sides receive a constant voltage through the battery voltage supply circuit. The normally closed contacts are connected to ground and the control side is connected to the BCM. Once a door lock or unlock request has been received by the BCM, the BCM will ground the control side of the appropriate relay. This energizes the relay and allows voltage to be applied to either the door lock motor lock or unlock circuits. since the other side of the door lock actuator is connected to the normally closed contacts of the opposing relay to ground, the doors lock or unlock.

Yes, I have a suggestion: diagnose the problem with your door lock actuator or the door lock actuator circuits to your trunk.

door lock actuator might be faulty or bad electrical contact
take off the door panel and diconnect and reconnect the wiring, you might need to change door lock actuator

Hello. The power windows each need a new window motor assembly which includes a new track system. The advantage to the assembly is that it is very difficult to remove the motor and install a new one. the power door locks on the passenger side the most likely cause is the power door lock actuator, about a ten dollar part.

You should replace power door lock at front passenger side, you can use any 'universal' power door lock. its an unit with a small motor inside that have a mechanism to up and down according electricity from the actuator (master door lock at driver side)
Hope this help :-)

lock actuator is bad...

You may need to remove your door panels (screws are by the door handle, arm rest, under door and side of door) and then peel back the weather film on each door to see what could be causing the issues.. rusted wires, loose connection, broken linkages, seized linkages. I'm not sure what to do with your car since each door seems to be having a different issue, but I would check the locking mechanisms..

Probably the door actuator - a part inside the door that activates the lock, particularly if neither the interior lock switch or the remote do not lock the door.  Once the doors lock the horn will beep again - the lack of beep indicates the vehicle is not secure.