Ok, my son was "helping" me work on my car, and was pressing the one touch feature on the seat motor. It would move a little, then stop. He did this until the seat was all the way forward, but then it wouldn't one touch back... ugh... The door controls also no longer work to move the seat back and forth. I checked all fuses, and we are good there. I also checked the signals from the door using my autel scanner, and the computer is recognizing the requests from the door as you can see the digital responses in the software. I also pulled apart the one touch switch. There are 3 wires, red has 12V, the brown has ~10 volts and the 3rd wire has almost no voltage... With the brown being at 10V, is that telling me that i have shorted out my ground in the seat control module? Does anyone have a wiring diagram of this seat control module and one touch? Dare I ground out the brown wire to see what will happen?? Thanks for any help on this!

2004 SL500

 

Are you talking about the switch to access the rear compartment? If that function isn't working, I would start by fully normalizing the seat in the seat module. If the seat loses track of its position, it gets very reluctant to move anywhere. It is programmed to avoid hitting the roof or anything else, so those safety functions can prevent movement. Also check for codes in the seat module. If it loses a hall sensor on any of the motors, it will do the same thing, but that will throw a code.

 

Yes, the switch to access the rear compartment. How do you fully normalize the seat in the seat module?

 

Update: The seat control module is not communicating... fudge... that means that it could be an open or power issue or a fried module...It is probably best to remove the seat... This is going to suck because the seat is all the way forward and it will be difficult to remove the seat..... green connector is the power to the forward/backwards motor... ugh

 

Final update.... The main ground on the seat controller under the seat was open. So, making the connection to ground has fixed the problem. This seems to be a common problem on this car, and it could be that as it is getting older, the wiring is failing. Does anyone know what ground this is supposed to go to? I would imagine the right footwell ground W36, but I don't have the wiring diagram.

 

Root root cause... passenger footwell ground was loose! Tightened up and we are good! Likely inadvertently loosened when removing plate over bass speaker. Killing myself.

 

The fact that you have 12V on the red wire indicates power is reaching the switch. The brown wire showing around 10V could mean it's partially grounded, suggesting a problem with the ground connection or the module itself. I wouldn't advise grounding the brown wire directly, as it could lead to further damage. Instead, consult a wiring diagram specific to your vehicle's seat control system for accurate diagnosis. Checking the ground connection to the seat control module would also be a good step.

 

It sounds like the issue with your R230's seat motor could stem from a few potential causes. Given that the seat moves slightly and then stops, it could be a problem with the seat control module itself, possibly a faulty or failing component within that module. The fact that there is a voltage discrepancy (with the brown wire showing around 10V instead of a consistent ground or 12V) suggests there might be a grounding issue or a problem with voltage regulation to the motor. The motor could be encountering resistance due to a mechanical obstruction or a fault in the motor windings themselves, leading it to draw excess current and activate a protective stop. Opening the one-touch switch and noting the voltages was a smart move—it shows a power supply issue, so it's worth checking connections thoroughly for corrosion or loose contacts that might be impeding the current flow. For further diagnostics, I would recommend reading the fault codes from the Body Control Module (BCM) and possibly the Seat Control Module (SCM) to get a more precise idea of where the problem lies. A full system scanner would be ideal for this, as it will read all the systems in your vehicle. I've been using the youcanic full system scanner for diagnostics, which has been effective across various vehicle systems, including seats. If you're opting for a more basic code reader, one commonly used model is the Actron CP9125, which unfortunately only scans the engine. However, given your issue, a full system scanner is necessary to identify non-engine related issues accurately. Make sure to check these modules and if you've gone through all the usual suspects like fuses, relays, and basic connections, it's likely a deeper electronic fault. Have you already checked for voltage drops at critical connection points?

 

Thanks in advance of any help.