How to Solve Battery Drain Fault in 2003 Mercedes SL350
Quick and nifty roadsters were the talk of the town back in the early 2000s, as evidenced by the popularity of the Mazda MX5, Honda S2000, Porsche Boxter, and BMW Z4. It was a time when compact sports cars were the go-to for a lot of car enthusiasts and the manufacturers obliged. We saw one great model after the other from leading brands.
Soon, the number of competitors in the roadster segment skyrocketed, making it difficult for the average enthusiast to choose between the numerous options.
Most people waited for the dust to settle so that they could go for something that was a class apart. In other words, a car that was good in all departments. And as on cue, Mercedes released the SL350 roadster.
The SL350 took the world by storm when it first came out in 2003. The vehicle came out as the successor to the legendary 300SL Gullwing, and it lived up to its name. Enthusiasts from all kinds of backgrounds bought the SL350 and remembered the original Gullwing. But not only for its looks and performance, but also for its reliability.
For a sports car, the SL350 was incredibly reliable. To an extent that you can still find scores of this vehicle in top condition even to this day.
Those who own it will tell you that the SL350 is nothing short of amazing. It is a car worth buying and driving even though it is almost two decades old.
But if you would have asked Mr C a few days ago, the response wouldn’t have been too positive.
That’s because, quite recently, Mr C started to experience extreme battery drain in his 2003 Mercedes SL350. The unusual condition made the battery useless after 4 hours of use. None of this is acceptable in a car with the stature of the SL350.
Luckily, our client had the presence of mind to visit a mechanic at the earliest convenience. He went to his usual garage as soon as he possibly could, but they couldn’t solve his problem. The battery issue was too complex.
So, Mr C went out to look for a Mercedes specialist, and that is when he came across Garden City Garage. A google search and a quick read of all our great Google Reviews convinced Mr C that his Mercedes SL350 would be in safe hands.
Our client visited our Mercedes garage and talked to our seasoned Mercedes specialist, Thomas, to look for a solution.
Thomas listened to the client, and he tried to understand the issue, using the information provided by Mr C.
Once he had heard all the relevant things, our Mercedes specialist moved on to verify the client’s complaints.
Faults Found
Our Mercedes expert inspected the battery and used all the features that derive their energy from the car’s battery. Sure enough, the battery was completely flat, and it wasn’t able to power any of the items inside the vehicle that required an electrical feed.
The battery looked fine on the initial inspection, and there was no corrosion on the terminals. It looked like there was a deeper issue plaguing the client’s Mercedes SL350.
So, our Mercedes specialist wasted no time in moving past the verification phase and jumping into the next stage of the diagnostic evaluation.
Diagnostic Procedure
Our Mercedes technician began with the 15- step diagnostic procedure to rule out all the possibilities and single out the one issue that was affecting Mr C’s roadster.
Thomas started by fully charging the battery and then testing it for its integrity. But all that work turned out to be nothing fruitful. The battery had gone beyond the point of saving, and there was no way to revive it back to its optimal condition.
Our Mercedes expert had to replace the battery and perform a battery drain test on the new battery. The test gave alarming results.
To go into detail, the battery had a constant 2.2 amp drain that increased to 4.5 amps for a period of 5 minutes every 15 minutes.
It seemed like there was some other electrical component messing up the battery’s performance. Our Mercedes specialist started looking for that one part, and in his search, he stopped at the fuse box.
Thomas began testing each fuse to see if the current was flowing through the vehicle when it was locked. This test normally leads to one or two fuses that are functional even when the car is locked. In this case, it was soon obvious that there was a network issue because almost all the fuses on the driver’s rear and front Signal Acquisition Module (SAM) modules had current flow.
The only thing left to do now was to test the Controller Area Network (CAN) diagrams and search for a point to scan the engine and interior CAN.
As soon as our Mercedes specialist performed this test using an oscilloscope (yes, it’s not just hospitals and scientists that use them!), he found out that the interior CAN was alive even when the car was locked. The interior Controller Area Network was draining the battery ever so slightly, leading to a completely flat battery in four hours.
Solving The Problem
Once the diagnosis was done and dusted, our Mercedes technician could move towards employing the solution.
He started by going to the interior CAN network location and shutting off each module individually until the network stopped communicating with the central unit. Interestingly, the interior CAN has 42 control modules, and in Mr C’s car, it was the 42nd module (related to the vehicle’s central locking) that was the culprit. Once Thomas turned that off, the battery received some much-needed respite.
But the solution was still not in place. Our Mercedes technician had to install a brand-new Pneumatic control module for the central locking system to solve the internal issue.
If he had not put the new component in place, the central locking module would have drained the battery yet again. Once the fix was in place, all the modules started shutting down automatically, and after 35 minutes, the battery drain came down to 0.05 amps.
Afterwards, our Mercedes specialist programmed and SCN coded the module, redid all the tests and found no irregularities in the entire system.
Summary
We used our experience and knowledge of cars to solve a complex battery drain case quite recently. A client came into the Garden City Garage, complaining about the performance of their car’s battery.
Our Mercedes technician inspected the vehicle and determined a deeper issue was plaguing the battery. Thomas wasted no time using the 15-step diagnostic procedure to get to the root of the problem. He found that the CAN network in the client’s 2003 Mercedes SL350 was malfunctioning. More specifically, the interior CAN was out of order, allowing the 42 internal modules to work at all times.
Our Mercedes specialist worked his magic and solved the problem in a jiffy! Not only did he save the client’s time, but Thomas got to the root cause of the issue.
If you are looking for a Mercedes garage that provides great value and gets the right diagnosis every time, look no further than the Garden City Garage. You can contact us on 01639 701604 to learn more about our services.
