Mercedes

Have Mercedes Questions? Ask a Mechanic for Answers ASAP

Ask an Expert,
Get an Answer ASAP!

Mercedes

Liftgate power lock motor won't actuate lock on a 2003

Customer Question
Liftgate power lock motor won't...
Liftgate power lock motor won't actuate lock on a 2003 ML350. Motor checks OK, but when actuated only 1/2-1 volt or so, is momentarily present at the motor plug when connected to a Fluke meter.
JA: How many miles are on the car? Is it an automatic or a manual transmission?
Customer: auto, 120K give or take.
JA: Are you fixing your ML350 yourself? What have you tried so far?
Customer: Checked the lock actuator motor for proper function, it checks ok. Noticed it wasn't working after replacing the lock actuator in the front passenger door. No idea if the liftgate problem just happened or if nobody had noticed it yet.
JA: Anything else you want the mechanic to know before I connect you?
Customer: Not that I can think of.
Submitted: 3 months ago.Category: Mercedes
Show More
Show Less
Ask Your Own Mercedes Question
Answered in 37 minutes by:
8/5/2017
Mercedes Mechanic: Mechanic01, ASE Certified Technician replied 3 months ago
Mechanic01
Mechanic01, ASE Certified Technician
Category: Mercedes
Satisfied Customers: 1,153
Experience: Owner at Baltic investments
Verified

Hello my name is ***** ***** I will be assisting you with all of your vehicle questions today. Give me one moment while I review your question and come back with a answer. Please be aware I do not know your skill level or abilities so I will be asking a lot of questions and in a lot of cases we will respond to each other quite a lot before we find a solution. As far as phone calls are concerned that is the system prompting you, not me, and they do cost more money, I prefer text but in some cases a phone call is required.

Ask Your Own Mercedes Question
Mercedes Mechanic: Mechanic01, ASE Certified Technician replied 3 months ago

Have you checked the relay yet?

Ask Your Own Mercedes Question
Customer reply replied 3 months ago
Not sure, the only relay I have found in under the hood and appears to operate all the power locks. The other 4 doors operate normally but I did do the swap relay trick with no change. If there is a separate relay dedicated to the liftgate I haven't found it. I am assuming the relaly on the lift gate is part of the electric de-fog circuit?I don't have a wiring diagram so I am a bit in the dark here.
Customer reply replied 3 months ago
As far as skills, I'm not an auto mechanic, I fix more airplanes than cars but have a better than average grasp of troubleshooting and diagnostic procidures. Without a wiring diagram to depict how they designed the circuit I am at a dcided disadvantage!
Customer reply replied 3 months ago
I tested the operation of the lock actuator with a 9V battery, (like the one in a smoke detector) so not to toast anything. It functions normally in both directions.
Customer reply replied 3 months ago
I will go look... I acts like bad contacts, only a volt or so is showing up at the actuator connector when the locks are operated.
Customer reply replied 3 months ago
Found the relay and swapped it with an adjoining one with the same p/n, no change. You can hear the actuator try and move when you activate it but there is insufficient current making it to the motor to do anything. The flute meter is only showing a momentary 0.8 - 1.0 VDC + or - depending. on if you are locking or unlocking.
Customer reply replied 3 months ago
I'm going to check for a bad ground. Looks like term A should go to ground.
Mercedes Mechanic: Mechanic01, ASE Certified Technician replied 3 months ago

I would also jump 5 to 3 and see what your getting on there, it should work if your doing that if not there will be a fault shown in the ground

Ask Your Own Mercedes Question
Customer reply replied 3 months ago
OK, jumping 3 and 5 do nothing.I can drive the lock to both positions by swapping the a and b on C2 between ground and either of the gray and white wires and the brown wire on C1 has ground continuity.One difference I see is this diagram depicts a pink wire where this car has a green wire.The issue appears to be a ground issue, the motor side of the gray and white wire will drive the lock either direction by reversing the polarity, what is the function of the other two wires? Seems it should operate by simply swapping the polarity of the gray and white, but it doesn't appear to work that way, they both seem to provide 12VDC?
Mercedes Mechanic: Mechanic01, ASE Certified Technician replied 3 months ago

when you jumped 3 to 5 what did you have when the circuit was complete?

Ask Your Own Mercedes Question
Customer reply replied 3 months ago
Same as when the relay was installed, a feeble click and that's it.
I will be busy flying all day tomorrow so I will get back with you when I get done. If you could send more of the wiring diagram so I can see the function of more of the wires I will ring out the harness a bit more for proper function.Also if you have something on the motor, I'm having a hard time getting my head around the ground path, and that appears to be the source of the problem. If the ground path is supposed to come thru either of the wires on C2, it isn't. If it is supposed to come thru the brown wire on C1 the fault must be inside the motor assembly.
Customer reply replied 3 months ago
I was thinking, is there a switch in the latch that inhibits the operation of the power lock when the liftgate is ajar like the cabin doors? This vehicle had issues with the latch comming loose preventing the door opening. Is there a switch/sensor in that latch assembly that could have been damaged that is now preventing the system from operating normally?
Mercedes Mechanic: Mechanic01, ASE Certified Technician replied 3 months ago

Not from the diagram im lookinf at but I dont have more info on that system so ill open this back up to the other techs to see if they have something that could help

Ask Your Own Mercedes Question
Customer reply replied 3 months ago
thanks,There are two additional wires coming out of the lock motor, one of which appears to be a ground. If these are part of the actuation circuit it would explain why I can operate it manually with a 9V battery.The main question I have is where does the ground (-) path for the motor come from, the relay box up front or the brown wire in the back?
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 3 months ago
Lou P. master tech
Lou P. master tech, Mercedes Technician
Category: Mercedes
Satisfied Customers: 5,070
Experience: 15 years master certified 100% fix rate and have access to factory radio codes, wiring, and instructions.
Verified

Hello, my name is***** and I will do my best to assist you.I am going over your story now and will reply back soon with some info,thanks!

Ask Your Own Mercedes Question
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 3 months ago

ok on the motor there are 2 plugs, we are interested in the small 2 pin plug with the white wire and pink wire, does that agree with what you are looking at?

Ask Your Own Mercedes Question
Customer reply replied 3 months ago
the small plug. But on this vehicle the wires are green and brown, no pink.The lock can be driven to either position if you supply a ground to one or the other of the pins on the other (bigger) plug and (+) from the factory wiring. Swapping the ground, or the operation mode (lock/unlock) will reverse the operation.
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 3 months ago

ok, that is odd that the wiring does not match, can i have the build date on the drivers door sticker?

Ask Your Own Mercedes Question
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 3 months ago

also what i want you to do since you located the proper wires, use a meter to ground and check either wire for positive when locking or unlocking, and then check the wires for negative , lets see if we are missing 1 switched signal or both signals on a certain wire, hope that makes sense, since its the same motor the polarity will change when locked and unlocked. if we are missing positive and negative on 1 or bother wires that tells me we have a wiring issue, if we are missing just on 1 wire that tells me wiring issue, if we are getting one voltage source but not the other it tells me control module issue or relay issue. . also as a side not this is the only model that the mercedes diagram does not give us diagnostics for but each wire has print on it, it tells where the wire connects to and from. its pretty neat . hard to read but the wire shows the connection and terminal number.

let me know what you get on each wire. both positive and ground when locking and unlocking,. that will open op doors for us, no pun intended.

Ask Your Own Mercedes Question
Customer reply replied 3 months ago
05/03
VIN 4JGAB57E83A451961
(+) on either wire depending on lock or unlock, No (-) on either. If you connect a Fluke between the two wire you get a momentary voltage of less than a volt during actuation. If you connect one wire or the other to a good ground you get a solid 12+ for a second or so when the locks are actuated, one wire or the other depending on the direction of operation.
Customer reply replied 3 months ago
the small brown wire on the small plug appears to be a ground. No clue what the green wire is for.
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 3 months ago

perfect. let me get at the diagram, be right back.

Ask Your Own Mercedes Question
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 3 months ago

ok on the latch, there are 2 connection, a 2 wire and a 3 wire that only has 2 wires in it correct?

Ask Your Own Mercedes Question
Customer reply replied 3 months ago
The problem appears to be with the ground path. Either it is broken somewhere or it is inhibited by a switch somewhere, hence my interest in the function of the other wires.
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 3 months ago

on the 3 pin connection i see that the brown is ground and the other that shows me to be pink goes back to the aam module which tells me its most likely a signal wire that shows the lock is activated or what not.

the wires we are concerned with are in the 2 wire connection. which im sure we are on the same page with.

so ...............

Ask Your Own Mercedes Question
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 3 months ago

the grey wire and white wire should both be grounded at rest. the grey wire grounds through relay k15 terminal 4, and when lock or unlock happens the relay is activated to close to terminal 3 which sends positive on the wire . so lets make sure that relay k15 is correct and has all the proper terminals. should be a 5 pin relay.

the same is said for relay k20. since we have positive that tells me that the relays and wiring is good, the issue may be a faulty relay or a relay that is not correct. let me know !!

both relays are located in the engine bay fuse box.

Ask Your Own Mercedes Question
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 3 months ago

here is what i am looking at .

m14/7 is the latch, you can follow along i hope . its not hard but not easy lol, the 30 is battery power, the 31 is ground. that way you can tell where i am getting the info from for the wiring and polarities.

Ask Your Own Mercedes Question
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 3 months ago

legend

Ask Your Own Mercedes Question
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 3 months ago

as you can see this is genuine mercedes info, not ***** *****ke what was given to you earlier.

Ask Your Own Mercedes Question
Customer reply replied 3 months ago
I am making the assumption they are good, First thing I did was swap them with others in the box with the same p/n. No change.I will confirm.The liftgate latch had some issues some time ago, it was slammed shut in the closed position and required some persuasion to get it to operate again. Any chance there is a switch attached to the latch that was damaged the is inhibiting proper operation?
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 3 months ago

this is a simple circuit, at rest the wires have ground, when activated a certain relay will activate and apply power .

this car is not smart lol, its a very basic system hence all the relays. there are 5 total i think for the locking system, :(

Ask Your Own Mercedes Question
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 3 months ago

and yes no assumptions, we confirm.

Ask Your Own Mercedes Question
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 3 months ago

i will have to leave for a bit but can return later. feel free to reply as much as needed i will reply when i can but be on full time later today.

Ask Your Own Mercedes Question
Customer reply replied 3 months ago
With the diagrams, I have a place to start other than just poking and guessing....
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 3 months ago

good deal. again the problem with this car is mercedes never gave us diagnostics on what signals happen when. so you have what i have.

let me know what you find with the ground. we should have ground on both wires at rest.

Ask Your Own Mercedes Question
Customer reply replied 3 months ago
OK, here is what I have found, the problem appears to be in the control circuit when lock command is given both K15 & K20 are energised. At rest both the white and gray wires are Lo and when both are Hi when the lock button is depressed, Nothing for the unlock command, 0.8-0.5V for a second or less.No wonder it doesn't work! If I provide a ground to one of the pins on the motor I can drive the motor with either of the leads using the lock command, reversing the polarity on the motor drives it the other way with the lock command withe either wire...
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 3 months ago

ok, good deal, i am getting the diagram back up and will report back.

Ask Your Own Mercedes Question
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 3 months ago

ok so the problem has to be in the k15 ground activation circuit for the relay correct? because if the other relay had an issue none of the locks would work. is this correct? from what i am seeing , if so our ability to diagnose is about to get very slim. if the issue is limited to the activation circuit of the k15 relay then either the pin on the aam is bent or the aam is not activating it and we need a scanner to diagnose it further to see if we can activate it with the scanner.

Ask Your Own Mercedes Question
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 3 months ago

pin 4 on the aam, the aam is the all activity module and it is connected to the bottom side of the fuse box in the engine bay.

it is easily removed. then you can check all the pins to see if any are bent especially pin4 .

so let me know what you decide to do but hey man we are there.

Please take a second and click the stars at the top of the screen to rate me so i may receive my credit , 5 stars is ideal , please request me in the future.Keep in mind then when you rate it does not end our conversation, you can still return here to me for follow up information if needed just simply reply back, thanks!
Lou P.
Master Mercedes-Benz Technician
Master ASE Certified

Ask Your Own Mercedes Question
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 3 months ago

any progress??

Ask Your Own Mercedes Question
Customer reply replied 3 months ago
Haven't had a chance to get back to the car project, I have had a couple airplane cylinders that needed changed and a turbo issue on another plane that needed my attention first.
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 3 months ago

gotcha, always thought it would be cool to work on airplanes but there is no room for error. pretty sure you dont get comebacks. sorry to bother you, let me know.

Ask Your Own Mercedes Question
Ask Lou P. master tech Your Own Question
Lou P. master tech
Lou P. master tech
Lou P. master tech, Mercedes Technician
Category: Mercedes
Satisfied Customers: 5,070
5,070 Satisfied Customers
Experience: 15 years master certified 100% fix rate and have access to factory radio codes, wiring, and instructions.

Lou P. master tech is online now

A new question is answered every 9 seconds

How JustAnswer works:

  • Ask an ExpertExperts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional AnswerVia email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction GuaranteeRate the answer you receive.

JustAnswer in the News:

Ask-a-doc Web sites: If you've got a quick question, you can try to get an answer from sites that say they have various specialists on hand to give quick answers... Justanswer.com.
JustAnswer.com...has seen a spike since October in legal questions from readers about layoffs, unemployment and severance.
Web sites like justanswer.com/legal
...leave nothing to chance.
Traffic on JustAnswer rose 14 percent...and had nearly 400,000 page views in 30 days...inquiries related to stress, high blood pressure, drinking and heart pain jumped 33 percent.
Tory Johnson, GMA Workplace Contributor, discusses work-from-home jobs, such as JustAnswer in which verified Experts answer people’s questions.
I will tell you that...the things you have to go through to be an Expert are quite rigorous.

What Customers are Saying:

I would (and have) recommend your site to others I was quite satisfied with the quality of the information received, the professional with whom I interacted, and the quick response time. Thanks, and be sure that I'll be back whenever I need a question answered in a hurry.

Stephanie PElm City, NC

used your service this weekend with "Trecers" help. thank you ,thank you, thank you. replaced an A/C fan motor. Local Auto Zone had part. $15.00 "tracer" fee and $40.00 for parts, I saved several hundreds of dollers at a shop. i will recommend you and use you in the future.

David L.Richmond, TX

9 dollars, 2 hours of my time, and I drove away. Your diagnosis was right on the mark. Thank you so much.

PhilMarysville, CA

Lurch. Thank you very much. I had real doubts about this website but your promptness of response, quick followup and to the point answer with picture was incredible.

CharlesWalnut Creek, CA

As a single woman, I really appreciate an excellent and affordable opinion.
Thank you Geordie, I will not hesitate to contact justanswer in the future!

SueCharleston, WV

Another great insight to what may be the problem. I will have my mechanic take a look at it tomorrow. Thanks again, Frank...you do indeed know your stuff.

JimCastleberry, FL

Wonderful service, prompt, efficient, and accurate. Couldn't have asked for more. I cannot thank you enough for your help.

Mary C.Freshfield, Liverpool, UK

< Previous | Next >

Meet the Experts:

MB Paul

MB Paul

Mercedes Technician

3,567 satisfied customers

Qualified Mercedes Benz Diagnostic Technician - 20+ years experience - Workshop Foreman for Mercedes

Marty

Marty

Mercedes Technician

28,773 satisfied customers

Bosch Certified Master Tech. Over 35 years experience.

Lou P. master tech

Lou P. master tech

Mercedes Technician

5,070 satisfied customers

15 years master certified 100% fix rate and have access to factory radio codes, wiring, and instructions.

Michael Warfield

Michael Warfield

Factory Mercedes-Benz Technician

3,131 satisfied customers

Mercedes-Benz Master Certified technician

Matt

Matt

Engineer

591 satisfied customers

Mechanical Engineer with 23 years experience in the auto industry, 8 yrs in formula 1 engine testing

promerc

promerc

mercedes diagnostic technician

553 satisfied customers

Qualified mercedes diagnostic technician & service team manager , ATA registered Master tech

Hipo64

Hipo64

Mercedes Technician

443 satisfied customers

Work and diagnose electronics on daily basis.

< Previous | Next >

Related Mercedes Questions
2003 Mercedes E320 Serious battery drain. Battery is
2003 Mercedes E320 Serious battery drain. Battery is draining within in hours after being fully charged.… read more
Chad Farhat
Chad Farhat
Owner
Associate Degree
3,996 satisfied customers
Car wont start but the Aux. battery malfunction is on in
Car wont start but the Aux. battery malfunction is on in display. I had the battery checked and its good … read more
Pete
Pete
Independent Auto Technician
Vocational, Technical or Trade Scho
138 satisfied customers
Regarding that Mercedes --I didn't mention that the battery
Regarding that Mercedes --I didn't mention that the battery was completely flat and we had to jump the car to get her on her way but my wife only made it about 2 miles before the car shut off. Have no… read more
Marty
Marty
Mercedes Technician
Associate Degree
28,773 satisfied customers
Stepped on gas pedal hard yesterday and transmission slipped
Stepped on gas pedal hard yesterday and transmission slipped revved and went back into gear. Lost race mode, shifting pedals not working. Car moves in forward and reverse, AAA car home instead of burn… read more
Marty
Marty
Mercedes Technician
Associate Degree
28,773 satisfied customers
After the battery died, the radio prompted for a code. The
After the battery died, the radio prompted for a code. The wrong code was entered on accident (have the right code and have successfully entered it before to get the radio to work). It has been stuck … read more
Edward Clayton
Edward Clayton
Associate Degree
1,033 satisfied customers
I just replaced the battery for my 2003 e500, but my battery
Hi, I just replaced the battery for my 2003 e500, but my battery seems to be draining overnight. … read more
Lou P. master tech
Lou P. master tech
Mercedes Technician
5,070 satisfied customers
Transmission problems. Won't shift out of first and wont
Transmission problems. Won't shift out of first and wont move in reverse. Happened twice and I am scared that it will leave me stranded. I am retired and bought a Mercedes for its reliability It shoul… read more
Eurocar Inc
Eurocar Inc
Master Audi/VW Tech
Associate Degree
1,773 satisfied customers
Battery location on my C300 2014 auxiliary battery. I I
battery location on my C300 2014 auxiliary battery … read more
Eurocar Inc
Eurocar Inc
Master Audi/VW Tech
Associate Degree
1,773 satisfied customers
I need to know the type of transmission and fluid type to be
I need to know the type of transmission and fluid type to be used on a 2002 Mercedes-benz S500. Also, is this vehicle RWD? Where can I purchase the transmission dipstick for checking the fluid level? … read more
eauto
eauto
self employed
High School or GED
74 satisfied customers
Dead battery. Unable to open trunk to get to the battery for
Dead battery. Unable to open trunk to get to the battery for jump start … read more
Matt
Matt
Engineer
Bachelor's Degree
591 satisfied customers
Feels as though the transmission is slipping on a 2008
Feels as though the transmission is slipping on a 2008 R320cdi....... happens when the trans comes up to temp and you get some jerking but mostly just engine speed that doesn't match wheel speed … read more
Lou P. master tech
Lou P. master tech
Mercedes Technician
5,070 satisfied customers
Instrument cluster do not work correctly ,transmission high
instrument cluster do not work correctly ,transmission high rpm before shifting when cluster fails … read more
Pete
Pete
Independent Auto Technician
Vocational, Technical or Trade Scho
138 satisfied customers
Two things, my battery was dead, I replaced the ba battery
Two things, my battery was dead, I replaced the ba battery and now the radio won't work I have tried the reset where are you disconnect the cables for a half hour we connect then put the windows up bu… read more
Lou P. master tech
Lou P. master tech
Mercedes Technician
5,070 satisfied customers
I want to change a bad battery. I can install the battery
I want to change a bad battery. I can install the battery myself. Are there any issues or codes that I need to consider. I am thinking about purchasing a replacement battery from I have. 2010 merceds … read more
kalamykid
kalamykid
Pactor automotive
Vocational, Technical or Trade Scho
97 satisfied customers
The transmission is in limp mode. Transmission fluid is
yes my airmatic system I put new struts in now if I let the car sit over night the air leaks… read more
Lou P. master tech
Lou P. master tech
Mercedes Technician
5,070 satisfied customers
My cars battery was jump started, then replaced battery,
My cars battery was jump started JA: Will the headlights turn on? Is the battery fully charged? Customer: then replaced battery JA: What is the model/year of your Mercedes? Customer: 2005 ml 350 speci… read more
Marty
Marty
Mercedes Technician
Associate Degree
28,773 satisfied customers
Won't start. Not battery and not remote key battery. They
Hi. Won't start. Not battery and not remote key battery … read more
Lou P. master tech
Lou P. master tech
Mercedes Technician
5,070 satisfied customers
ML 320. How to remove the main battery. This battery is
This battery is completely flat. I have a new battery thats bin checked … read more
Michael Warfield
Michael Warfield
Factory Mercedes-Benz Technician
Vocational, Technical or Trade Scho
3,131 satisfied customers
Disclaimer: Information in questions, answers, and other posts on this site ("Posts") comes from individual users, not JustAnswer; JustAnswer is not responsible for Posts. Posts are for general information, are not intended to substitute for informed professional advice (medical, legal, veterinary, financial, etc.), or to establish a professional-client relationship. The site and services are provided "as is" with no warranty or representations by JustAnswer regarding the qualifications of Experts. To see what credentials have been verified by a third-party service, please click on the "Verified" symbol in some Experts' profiles. JustAnswer is not intended or designed for EMERGENCY questions which should be directed immediately by telephone or in-person to qualified professionals.

Disclaimer: Information in questions, answers, and other posts on this site ("Posts") comes from individual users, not JustAnswer; JustAnswer is not responsible for Posts. Posts are for general information, are not intended to substitute for informed professional advice (medical, legal, veterinary, financial, etc.), or to establish a professional-client relationship. The site and services are provided "as is" with no warranty or representations by JustAnswer regarding the qualifications of Experts. To see what credentials have been verified by a third-party service, please click on the "Verified" symbol in some Experts' profiles. JustAnswer is not intended or designed for EMERGENCY questions which should be directed immediately by telephone or in-person to qualified professionals.

Show MoreShow Less

Ask Your Question

x