GeekDiyMechanic - 2010 BMW X3 Battery Change Case Study This is a strange one indeed. After about a week or so, she was able to take her car into her long-time trusted European car specialist. She was also noticing more issues with her X3 since she last spoke with me. For example, the intermittent wipers could not be adjusted in frequency. They would only work at one speed.
She was only able to tell me what the mechanic told her. Unfortunately, the mechanic did not detail what he found or how he exactly resolved what he found. The mechanic indicated that there was a short in the DTC terminal area that fried a wire yet did not blow any fuses.
It appears that the place where they installed the new battery caused the problem, since that is when the problem started happening. The mechanic felt that when they plugged in their scantool, it somehow damaged the DTC port. I found it interesting that neither the car nor the scanner blew a fuse, yet a wire burnt up. Lastly, they replaced the battery as well.
Although the mechanic found the DTC port damaged, using my scanner, I connected to DTC port with no issues. Lastly, the mechanic asked her to not allow anyone to connect to the DTC port unless he gives his permission.
So, in the end, not actually knowing what was wrong with car, all of the information in this write up has no merit. I have no way of knowing if the PCM was turning off circuits or the circuits were damaged causing her issues.
The best way to look at this case study is how NOT to execute a diagnosis.
A friend of mine changed the battery in her very nice BMW 2010 X3 and, unfortunately, started to experience some weird car behaviors.
In a proactive fashion, she noticed that her car was cranking slower and slower, so she headed to a local automotive retailer and purchased a replacement battery. She upgraded from a H6 to a H8 battery.
Here’s the rub. Ever since her battery change, her clock will not keep date and time. Following the Owner’s Manual, she set the date and time. But once she turns off the car, the date and time are lost the next time the car is started.
My friend called me and described his wife’s car's issue. I asked questions, but I made my first mistake. I should’ve asked to speak to her directly to obtain more information. Always get as much information from the car owner before starting research. But, I didn’t.
My friend executed the following tests for me:
From this first call, I was told that the battery was upgraded from a H6 to a H8. My friend said that his mechanic told him that they would have to change the battery type set in the PCM.
Here’s where I made my next mistake. I first looked up the difference between a H6 battery and a H8 battery. Since I was on a battery manufacture’s web site, I believed the information to be correct. It stated both batteries were equivalent other than the H6 was a wet type and the H8 was a dry type. I later learned that the M8 battery is physically slightly larger and more available amps. Many people suggest this upgrade especially if you live in cold weather.
I made another big mistake. I assumed that since the battery type was different, which it isn’t, that the voltage might be different. I, improperly, assumed that since the battery was recently installed, new, and was a different battery type (wrong), that the voltage was ok to be lower. Big mistake.
I researched about other BMW’s not being able to keep time. After much digging, numerous articles indicated that if the PCM senses a low battery voltage, it will shut down unnecessary circuits in the car when powered down to try to maintain enough battery power to start the car. Therefore, that would explain why the date and time circuits would be cleared after the car was turned off.
This is where I usually excel. But, in this case, I did not. I should have requested to have ample time with the car to properly diagnose issue. I should have also accessed an online manual, for example, Mitchel DIY Online or AutoZone DIY Online, to determine powers and grounds to the clock circuit. I should have then determined if the circuit was losing power when the car was turned off. If I could verify that, I should have then hooked another stronger battery in parallel to increase system voltage to around 12.5v. I would then execute the same test to determine if the PCM would still power off this circuit. If the circuit this time kept its power, I found the true cause of the issue. If not, I could have dug further to determine the root cause of the issue.
But instead, when they came by, I used my friend’s DVM to measure battery voltage, which was 12.1v. When the car was running, I performed a voltage drop test to determine if the battery terminals were good, and they were.
I then hooked up scantool in hopes of finding a function to signal the PCM that a battery change occurred. After much probing, I did find an Advanced Functionality menu item which contained a function to indicate a battery change. We were all so happy, but not for very long. We executed the function, which had to be done with engine off. Once it completed successfully, we tried to set the date and time following the Owner’s manual. But unfortunately, it did not maintain the setting. We then took another five minutes looking all around the scantool menus looking for a way to change battery type. What was strange is that the instructions on the menus indicated there should have been a menu option to change the battery type. So, I thought I was on the right track. But, I could not find it. So, thinking that my scantool did not have that functionality and only a BMW specialist might have a manufacture scantool with that option, they decided to make an appointment with a professional BMW mechanic. They were able to get it in the same day, but after waiting over an hour (crazy), the mechanic indicated his scantool did not have the option either and rescheduled her for about a week later.
So, sadly, this case study teaches a little technical information but mostly teaches what not to do. In any case, I hope you learn from my little successes and from my big mistakes.