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Dick Hussey's Tech Corner

Diagnose Common Problems in Latches and Door Locks

There are two different styles of door locks and latches used on the 1987 through 1993 model Allantés. The first style was used on 1987 through 1992 models, and the other style only on 1993 models. The following will help you diagnose and repair the most common problems that occur with door locks and latches.

 

The first issue is the lock cylinder switches. All Allantés have lock cylinder switches. One type was used on 1987 through 1992 models, and the other only on 1993 models. The micro-switch itself is the same across all years, but the wiring connector is different. Picture 1 shows the early lock cylinder with switch on the left, and the 1993 version on the right. In between there is a '93 switch by itself, not installed into the lock cylinder. On Picture 2 you see the back of the lock cylinders with the switches nestled into their location. The function of the lock cylinder switch is to send a signal to the body computer module (BCM) when the door is being unlocked with a key. The purpose of this signal is two-fold: to send "wake-up" voltage to the computer system, and also to disarm the cars anti-theft system. What can go wrong: the switch can either fail on or not send the signal to the BCM.

 

When the switch fails on, a constant signal is sent to the BCM. The car's computer system does not go to sleep or into standby mode. This results in a dead battery within two to three days if the car is allowed to sit unused for that long. If the car is used every day, you could have this problem and not even know it. When the switch fails to work at all and does not send the signal co the BCM, it also fails to send the signal to the anti theft system. Under this condition, turning the key has unlocked the door mechanically so you can open the door, but because the antitheft system has not been signaled, the alarm will sound. If this happens, try opening the other side door with the key to silence the alarm. Or, on 1989 through 1993 models, you can try turning the key TWICE in the trunk lock to open. One provision built into the Allantés on 1989 through 1993 models is that the second turn of the key in the trunk lock will serve to unlock both doors AND disarm the alarm system. This way, if you are (say) shopping and open the trunk to place your purchases, you can conveniently unlock the car from the trunk lock if you wish. The 1987 and 1988 models do not have this second turn of the key unlock feature. All models have a second turn of the key feature built into both front lock cylinders. If you wish to open both doors, just turn the key twice and the opposite door should open electrically with the second turn of the key. This feature can be useful when troubleshooting a problem with switches and door locks, or if mechanical linkage has come apart. If the door will not open with a key, try turning the key twice in the lock. Even though the mechanical feature may not be working, the power door lock solenoid could unlock the door electrically on the second turn of the key. Both door lock solenoids are wired together so any time a signal is sent, both receive the same signal.

 

There is provision in the on-board diagnostics to troubleshoot the lock cylinder switches. To do this, key on, car running or not (it does not matter), enter the diagnostics function by pressing and holding in both the OFF (not the blue) and WARMER (red) buttons on your driver information center AC control for about 5 seconds, then releasing after the dash display changes. Let the diagnostics process run until the "ECM?" or "PCM?" message is shown in the DIC message window . Press and release LO fan speed button to skip ECM/PCM segment. At "BCM?" press HI fan speed to select. At "BCM DATA?" press LO fan speed to skip, at "BCM Inputs?" press Hi fan speed to select. (On 1987 and 1988 models skip the following step as it does not apply.)

 

Then scroll up to BCM input parameter BI55 by pressing the HI fan speed button. If you go by it, press LO fan speed to return. The window should show "HI" and "O" on the left, and BI55 on the right. Insert the key in the trunk lock and turn to the right. If the switch is OK, the message will change to "LO" and "X". Turning the key back and removing it will change the message to "HI" and "X". If you are alone and cannot watch the screen and turn the key at the same time, if you see "HI" and "X" after turning the key, then the switch is OK.

 

After evaluating the trunk switch, if you have one, next scroll up to input parameter B161 using the HI fan speed button. Initially, the screen should show HI and 0 and B161. If the message window displays LO and X and B161, then one of your lock cylinder switches has failed on. Disconnecting the failed switch wiring inside the bottom of the door will change the message if the other switch is OK. To test the switch, insert the key in either exterior door lock cylinder and turn it to open. As with the trunk switch display, the window should change to LO and X if the switch is OK, then back to HI and X when the switch is released. To test the other side lock cylinder, switch and revert to the HI and O screen for B161. Use either the HI or LO fan speed buttons to change to another input parameter, then return to B161 and repeat the process.

 

The door lock solenoids themselves are totally different between 1987-1992 models and 1993 models. There is significant linkage on the early models, which can be troublesome. The mounts on the back of the door panel can get jammed when the door panels are reinstalled, and can also get rusted or restricted causing the door lock paddles not to move freely. This results in the door not able to lock, or unlock reliably when the door lock button is pressed. The linkage also complicates removing and reinstalling the door panels.

 

The 1993 system is not without its problems, however. The door lock solenoid is built into the door latch, so changing it is more difficult. And beyond that, something called the "door ajar switch" is built into the door lock solenoid assembly. Picture 3 shows two 1993 door latches, left and right. The door ajar and door lock solenoid assembly have been removed from the latch. If this part ever has to be replaced, it is critical that proper alignment is made between the teeth on the door ajar switch (Picture 4) and the teeth in the latch assembly. If misaligned, you will probably break the door latch when closing or opening the door.

 

On earlier Allanté models, there is a simple and reliable door jamb switch that signals whether the door is closed or open. On the 1993 models, if the door is not fully closed, the signal comes from the latch mechanism. When this switch malfunctions, the most common problem is to not signal the BCM that the door has been opened after the ignition has been turned off. There is a feature Retained Accessory Power (RAP) that will keep the radio and window switches and other features under power for about 10 minutes after the ignition is shut off or UNTIL the door has been opened. If your driver door ajar switch fails and the radio keeps playing, try opening the passenger side door to shut off the RAP.

 

The last important issue with respect to door latches is the tapered pin in the latch and mating hole striker found on the door pillar on 1987 through 1992 models (Picture 5). If your door needs to be closed hard to latch, chances are very good that these items need to be cleaned, or that the striker on the pillar needs to be replaced. The pin and the inside of the mating tapered hole in the striker must be CLEAN and DRY. NO LUBRICATION. Use WD-40 and a rag - keep spraying and wiping until all signs of discoloration is gone. When the pin is either lubricated or dirty, it makes the door very difficult to close. Also, if the hard rubber portion of the striker is worn or missing, no amount of cleaning will help very much. The striker will need to be replaced. Picture 6 shows a new striker on the left and a worn out striker on the right.