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sprinkles08, ASE Certified Technician
Category: Mercedes
Satisfied Customers: 22671
Experience:  ASE Master and Advanced level certified. Factory trained with 15 years dealership experience
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Yousef. Yesterday when I was driving everything was fine, I

Customer Question

Customer: Yousef. Yesterday when I was driving everything was fine, I stopped at a gas station, filled up, turned it on and moved maybe a block and ESP, Brake Sensor ABS light went off, the car would not shift past 2nd gear and I could not switch to manual or sports mode. I presume its a sensor issue I am just figuring out which one to replace
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Customer: I gave you all the details I have not connected the computer yet to check codes which I can in a little bit
Submitted: 1 year ago.
Category: Mercedes
Expert:  sprinkles08 replied 1 year ago.

Hello and welcome to JustAnswer!

You either have a speed sensor or ABS module issue. The ABS and related lights came on either because the ABS module saw an issue in the system and set a fault code, or the module itself isn't awake. The trans controller uses the rear wheel speed message from the ABS module as the transmission output speed, so if the rear wheel speed signal is missing then the trans will not shift.

The first thing that will need to be done is see what fault codes have set and if the ABS module is communicating. It's very possible that the ABS module is not awake either due to an internal failure or loss of power or ground.

Customer: replied 1 year ago.
There are no codes. When I turn the car off, it all resets. I have a drive a little bit or a lot to get it to fault again, but once again I have turn the ignition off and then on to get the computer to check codes and it turns up "no codes".
Expert:  sprinkles08 replied 1 year ago.

If warning lights are coming on there are fault codes, fault codes setting are the reason warning lights come on. Codes don't erase themselves, even if the warning lights go off the codes will still be present unless battery voltage is lost to the offending module.

What are you checking for codes with?

Customer: replied 1 year ago.
Actron auto scanner plus, hasn't had problems previously and do not think it is the scanner. All codes reset and functions restore the minute I turn off the car and then turn it back on. Did not pop up during on trip today but then 15 minutes later popped up on a different trip.
Expert:  sprinkles08 replied 1 year ago.

Do you have the actual model number? It may not be able to do what you need it to do.

Customer: replied 1 year ago.
CP9580A. Even that dash says "no faults". I forgot to mention, the speedometer goes out and the mileage doesn't read out digitally or on trip readings.
Expert:  sprinkles08 replied 1 year ago.

The speedometer and mileage issue are happening because the wheel speed distance from the ABS module is missing.

If you're picking the ABS module from a module menu and finding no codes then it's pretty safe to assume the ABS module isn't awake when this happens (there will be communication fault codes in all other modules that communicate with the ABS module, but you're not seeing them due to the code reader's inability).

An actual scan tool would likely be needed to prove that the ABS module isn't communicating during the event. After proving that the module isn't communicating then it's powers and grounds will need to be tested before condemning it.

Customer: replied 1 year ago.
what kind of scan tool would suffice?
Expert:  sprinkles08 replied 1 year ago.

An actual scan tool is a multi thousand dollar piece of equipment that you probably wouldn't want to purchase unless you use it professionally. If you have a laptop you might consider the AutoEnginuity software which has quite a bit of capability.

Customer: replied 1 year ago.
Sounds good, will be sure to take it to MB run diagnostics. However, when I was driving last night, the shifter ended up locking in park when I parked the car one time. I lifted the panel and found that now that have a little button on the back to disengage that. I have dealt with that problem before and replaced the shifter as well on a 01 CLK 430. Could this be a problem in connections with the previous ABS module or would this be separate of that and maybe a similar problem to what I had with eh CLK 430 and replacing the shifter.
Expert:  sprinkles08 replied 1 year ago.

The only way the shifter issue would be related to an ABS light is if both were being caused by the brake lamp switch, but that wouldn't explain the transmission issue and you'd also note the brake lights didn't work. It's more likely to be a shifter issue.

Customer: replied 1 year ago.
Well update, I do think the shifter and abs are linked. Double checked fuses and restarted car and shifter was unlocked and abs light gone. Came back shortly after. I ordered a used ABS module online and replaced it, and seemed to work well for a few trips then problem happened again. Will try pulling battery and resetting everything to see if that works. A new Module from the stealership is $1000 from one $1300 from another, $100 online used. They wanted to charge $189 to check the abs issue and another $189 to check the shifter. I am going to try to get the codes read somewhere cause scanner I bought couldn't read it.
Customer: replied 1 year ago.
Yea nevermind, battery disconnect didn't work.
Expert:  sprinkles08 replied 1 year ago.

The first step in diagnosing the problem will definitely be to find out what codes are setting.