Lincoln Towncar Backup Warning has "teenager's disease"


Much of the time the backup warning on my Lincoln Town Car does not want to work. It occasionally comes on and works fine for a while but then it disappears and a warning is displayed on the screen saying “backup warning is disconnected.” I suspect a loose connection, ground, or something like that. I took the car to the dealer and he wants to put a new one in to the tune of $650 but before I do that I want to ensure it is not just a connection. However, I cannot find the thing! Where on the car is the backup warning system module located? Am I wasting my time checking connections? What could I do differently?


Go to an independent mechanic, not the dealer. It sounds as if the dealer wants to replace every part of the system especially the electronics. An independent might be more prudent, testing the backup lights and maybe deciding only to replace a cheap switch. There are no guarantees; maybe you do actually need to replace some control module. It’s worth a shot.


I don’t think he’s talking about the backup lights. I think he’s talking about the sonar that warns him when he is getting close to something while backing up. Unfortunately, I don’t know where that module is on a Towncar. (This feature is sometimes called “rear park assist.”)


You’re right, it is the backup warning system. I hear now that the thing may be inside the back bumper under the plastic cover! If so, it is probably susceptable to mud, water, sand, etc. If I can figure out how to get to it, perhaps it may well be a fouled plug. Why would Lincoln put such an expensive system in a back bumper, covered by a thin plastic piece, where it is going to be frequently bumped by cars behind me? I swear there should be a 10th level in Dante’s Inferno reserved for automotive design engineers!


Well, the sonic transducers, at the least, are mounted to the bumper. There really isn’t anywhere else to put them where they would have the correct view behind the car. I don’t know if the electronics module itself is there too. It may be, they may have decided to keep everything together. In any event, I think that your theory that it is probably a connection is most likely correct. If you are lucky, it is at one of the connectors and you may be able to resolve it. If you are not so lucky, it is at one of the components soldered to a circuit board somewhere. If so, the assembly will have to be replaced as almost no one repairs at that level any more.
About connectors lasting in the mud, it can be done and has been done. For some reason (like poor quality control) you have a failure on that one system. I assume the rest of the multitude of electronics that the car has are still okay.


The warning system and the lights are likely on the same circuit using the same switch. I think SteveF has very good points.


Sorry, but if the Lincoln Towncar is anything like my Lincoln LS, that is not at all true. The message that he is getting on his data center display is very specific and it comes up only if the data center loses communications with the rear sonar module. It would not come up if the module just wasn’t being triggered by the powertrain module. (It doesn’t use a reverse switch for the backup lights or for the rear park assist. It uses CAN buss communications from the powertrain module to know when the car is in reverse. If the sensors/switches that are used by the powertrain module weren’t working right, he would have a lot more trouble than just the rear sonar. This is specific experience with those specific cars, not general guesses.)


CAN BUS. you know multiplexing.