What should have been an easy diagnosis turned out to have a very unusual problem.
This time out, the vehicle in question is a 2007 Buick Lucerne with an intermittent no start issue. We started with a quick code scan and retrieved a B3953 (Transponder Authentication error) and a B3055 (No transponder Modulation or no Transponder).
Clearly, we are dealing with some type of security system malfunction, and it seems to be a problem with the transponder in the key or the anti-theft antenna.
In order to get an understanding of how the system works, we looked up the system description in the service manual. Basically, this is a transponder key system. There is a transponder chip embedded in the head of the key, while the Anti-Theft module is mounted around the ignition key cylinder and contains an antenna that surrounds the key cylinder.
Halo and transponder
This antenna is commonly referred to as the Halo. When the ignition key is inserted into the key cylinder and turned to the run position, the anti-theft module energizes the Halo and sends out an electromagnetic pulse. The pulse excites the transponder chip in the ignition key. The transponder responds by broadcasting its encrypted code. The broadcast code is collected by the Halo and sent to the Anti-Theft module. The Anti-Theft module verifies the code and sends a message to the PCM telling the PCM that it is OK to start the car.
The codes we were receiving indicated that there was something wrong with communication between the Halo and the transponder in the key. The service manual procedure calls for trying a second key (which we did not have). If the car starts on the second key, then you replace the key. If the car will not start on the second key, you are instructed to replace the Anti-Theft module.
We do a lot of security problems and anti-theft programming and run into these situations quite often. In many cases a second key is not readily available. When we run into transponder and Halo issues, we use a tool called the Diagnostic Box. This tool has the capability to test the transponder in the key and the Halo.
When we tested the key on our Buick, the transponder responded every time. However, when we attempted to test the Halo, the Halo responded intermittently. The tester has a receiver that measures the electromagnetic pulse and displays the signal strength on a screen. We found that at times the pulse was weak or nonexistent. At other times the signal was strong. What was strange is that we had never encountered this before. Usually, the Halo either works or it doesn’t.
At this point we pulled the covers off the steering column to get a look at the Halo itself. As seen in the above picture, we found a coil of wire wrapped around the Halo portion of the Anti-theft module. Turns out that this coil of wire is the antenna for an aftermarket remote start that had been installed in the vehicle. We removed the coil of wire and the Halo started to work normally. There was nothing wrong with the system, the added coil was interfering with the Halo.
In this case, we concluded that the problem was created by adding an aftermarket accessory.
Mark Lemay is President of Auto Aide Technical Services. You can reach him at: [email protected]