[samosali]

The SRS is ocasionally on for some short moments.
The error scanner showed 3 blinks = driver's air bag.

My mechanic disconnected air bag and put a resistor instead of it into air bag's connector in the steering wheel. So the resistor simulates the air bag. the SRS light is still coming on, so now we know that air bag is not a culprit.

What is a culprit? Sliding rings in the steering wheel or/and sliding contacts? maybe something else? I do not want to spend several hundreds EUR to find out at the end that I bought a wrong part. Does anybody have any good idea how to test which section of the system before air bag is bad? Thanks.

 

[Mercedes Mechanix]

The SRS is ocasionally on for some short moments.
The error scanner showed 3 blinks = driver's air bag.

My mechanic disconnected air bag and put a resistor instead of it into air bag's connector in the steering wheel. So the resistor simulates the air bag. the SRS light is still coming on, so now we know that air bag is not a culprit.

What is a culprit? Sliding rings in the steering wheel or/and sliding contacts? maybe something else? I do not want to spend several hundreds EUR to find out at the end that I bought a wrong part. Does anybody have any good idea how to test which section of the system before air bag is bad? Thanks.

Your mechanic is savy and on task... substituting a 3 ohm resistor is a good and sound method of checking for an air bag culprit... but, also utilize a multimeter (Digital only... NEVER ANALOG!) and check the resistance of the air bag... ensure to secure the bag and use safety in mind when verifying same. If the bag is open... no resistance... the bag Could also be an issue and there is another area of opportunity...

The contact(s)... rings as you refer to them. These contacts are very likely to have built up a good amount of resistance due to oxidation and is a good idea to check them... or just go ahead and replace them before proceeding. I also would suggest another substitution of the 3 ohm resistor and then pull your codes again. Remember, there is more than one airbag and possibly an error in coded numerals gathered?

One question usually asked at onset... after codes are gathered... THE GROUND conductor on your battery IS disconnected... YES? ALWAYS disconnect the ground when hands on working with your SRS... and ALWAYS protect yourself by disarming the SRS as well! A validation of the vacuum/ pressure connections beneath the dash... Cluster area and the glove box and passenger footwell is also necessary.

READ PLEASE​

Certain vehicles include a driver's side airbag or a driver's and passenger's airbag, located in the steering wheel hub (driver's) or the dash on the passenger side (passenger's), as part of a Supplemental Restraint System (SRS) . Servicing, disassembling or replacing these items (including the ETRs) will require special caution and tools and should therefore be done by a properly trained technician.

WARNING: To avoid rendering the SRS inoperative, which can lead to personal injury or death in the event of a severe frontal collision, all maintenance must be performed by a properly trained technician.
Improper maintenance, including incorrect removal and installation of the SRS, can lead to personal injury caused by unintentional activation of the airbag.
All SRS electrical wiring harnesses are covered with yellow outer insulation, and related components are located in the steering column, center console, dash, and front fenders. Do not use electrical test equipment on these circuits.

Prior to disconnecting any SRS electrical connectors, servicing any system components or other components located near an air bag system electrical connector, the system must be disarmed. Refer to Air Bag System Disarming and Arming. Wait 10 minutes before starting any repairs. This is necessary to allow the system's back-up power supply to discharge.

Always observe the following safety measures when working on the air bag system:
SRS components must not be opened or repaired. Always install new components.
If air bag module, crash sensor or control module have been dropped from a height of 18 inches or more, do not install that component into vehicle. It must be replaced.
Always replace damaged SRS components.
Do not paint air bag module to correct cosmetic flaws. It must be replaced.
Do not leave an undeployed air bag module unattended if work is interrupted. Install into vehicle as soon as unit is removed from packaging.
Always store a removed air bag module with pad facing upwards.
Air bag module must not be exposed to oil, grease, or cleaning solutions.
Do not expose air bag module to temperatures above 195°F for even brief periods during a repair process. Keep unit clear of all heat sources.
Remove any SRS component prior to performing repair or welding procedures in area of that component.
Do not use electrical test equipment or analog ohmmeters on the air bag module.
Do not expose sensors, wiring or other SRS components to heat guns, welding or spray guns.
The SRS wiring should not be spliced, soldered or repaired. If wiring or connectors are found to be damaged or worn, that wiring harness should be replaced. When replacing the harness, ensure it is properly routed and all electrical connectors are securely installed.
Storage, transportation and disposal of air bag modules are subject to the laws for flammable solids.
Deployed air bag modules do not have to be disposed of as a hazardous waste, but may be included with automotive metal scrap for recycling.
Thoroughly wash hands after handling a deployed air bag module.
When handling a deployed air bag assembly, a face shield and rubber gloves should be worn. Vehicle interior and HVAC ducts should be vacuumed. If sinus or throat irritation is encountered during air bag removal, exit vehicle and breathe fresh air. If skin irritation is encountered, flush affected area with cool water. If any type of irritation continues, consult a physician. Wash hands and rinse thoroughly with water after handling a deployed air bag assembly.

Place tape over exhaust vents prior to air bag removal. After unit has been removed, it should be placed in a heavy duty plastic bag, sealed securely, then placed with automotive scrap. To dispose of an undeployed air bag assembly, contact Mercedes-Benz.​

Please ensure to never take ANY short-cuts when repairing your SRS or any part of. Also, usual conditions for checking... the contacts in steering beneath airbag... if any horn related complaints... recheck the ring contacts immediately. Also, check all seat-belt connector switches!

Good luck and email us if we can assist... will have a Technician assist as possible online. :thumbsup:

Dutch

 

[samosali]

Your mechanic is savy and on task... substituting a 3 ohm resistor is a good and sound method of checking for an air bag culprit... but, also utilize a multimeter (Digital only... NEVER ANALOG!) and check the resistance of the air bag... ensure to secure the bag and use safety in mind when verifying same. If the bag is open... no resistance... the bag Could also be an issue and there is another area of opportunity...

The contact(s)... rings as you refer to them. These contacts are very likely to have built up a good amount of resistance due to oxidation and is a good idea to check them... or just go ahead and replace them before proceeding. I also would suggest another substitution of the 3 ohm resistor and then pull your codes again. Remember, there is more than one airbag and possibly an error in coded numerals gathered?

One question usually asked at onset... after codes are gathered... THE GROUND conductor on your battery IS disconnected... YES? ALWAYS disconnect the ground when hands on working with your SRS... and ALWAYS protect yourself by disarming the SRS as well! A validation of the vacuum/ pressure connections beneath the dash... Cluster area and the glove box and passenger footwell is also necessary.

Thanks for your answer. if I understood you well I should check with digital multimeter if the resistance on the air bag connector is 3 Ohm. I should also clear the error codes before any action in the future. I must admit that we did not clear the error code 3 after installing the resistor. (But to be honest, I do not expect any change.)

the point is that I recently cleaned the contact rings in the steering wheel and the corresponding four contact tonguelets (with springs). I spent 2 hours on polishing them and cleaning them with special spray for slide contacts. All tonguelets and contact rings shined at the end with high gloss. So maybe there is a defect on a side which is not visible and whole assembly must be taken off (we just removed the steering wheel before polishing the contacts).

 

[Mercedes Mechanix]

SRS important information!

SRS, Clock spring contact center position
The correct centering of the clock spring contact is crucial for reliable operation of the SRS system and horn. The center position is maintained by the mounting screws before the clock spring contact is installed.
If the clock spring contact was turned out of the center position because:
^ the steering column joint was removed, or
^ the mounting screws were removed, the center position can be reestablished as follows:
1. Screw mounting screws completely into the clock spring contact assembly.
2. Turn clock spring contact to the right until resistance is felt.
3. Turn clock spring contact approx. 2-2.5 turns to the left until a position is reached where the mounting screws can be backed out so that the screw heads protrude through the holes to maintain the center position.
C. NOTES REGARDING TYPICAL STEERING RELATED REPAIR JOBS
Steering gear, removal/installation
CAUTION! Before sliding off the steering shaft coupling, allow the steering wheel lock to engage. After disconnecting the steering coupling, a set installation position can no longer be assured and the clock spring contact can be destroyed by excessive turning.

If in any doubt... change it out! This item (spring, rings... contacts as some refer too) is high on the diagnostic hit-parade (Robert's "Hip Pocket S-Klasse Reference book".... upcoming) as for causing SRS codes to be thrown relating to Drivers Air Bag squib. Only item higher on list are the seat belt retractors themselves... usually from debris being caught in switch assy.

Good luck and work safe,
Dietrich :thumbsup:

 

[samosali]

If in any doubt... change it out! This item (spring, rings... contacts as some refer too) is high on the diagnostic hit-parade (Robert's "Hip Pocket S-Klasse Reference book".... upcoming) as for causing SRS codes to be thrown relating to Drivers Air Bag squib. Only item higher on list are the seat belt retractors themselves... usually from debris being caught in switch assy.

Many thanks. So to conclude and to avoid any mistake: what exactly do you have in mind? So, ONE or TWO spare parts? I consider the contact ring(s) in the steering wheel as one item and the four little tongues which touch this ring(s) as another item. Are both of them equally dangerous in terms of throwing codes? best regards.

 

[Mercedes Mechanix]

SRS thought

Many thanks. So to conclude and to avoid any mistake: what exactly do you have in mind? So, ONE or TWO spare parts? I consider the contact ring(s) in the steering wheel as one item and the four little tongues which touch this ring(s) as another item. Are both of them equally dangerous in terms of throwing codes? best regards.

Dangerous with respect to safety measure for additional protection in event of an accident, etc... but the spring and contact face(s) can be a likely suspect in your investigation to satisfy a code... PLEASE remember... A code is simply a Symptom.... too many Techs will use a code as a "identify a bad part measure"... not correct and can be an expensive method of diagnostics! $$$$

Do you subscribe to alldatadiy.com? If not, subscribe.... will be best money you will ever spend on your vehicle.

After subscription... navigate to:
Vehicle » Restraint Systems » Air Bag Systems » Technical Service Bulletins » All Technical Service Bulletins » SRS/Horn Clock Spring - Introduction

If you are unable to get with alldatadiy.com.... drop us an email to [email protected], will ask one of my Techs to assist with some images (from WIS/ STAR but compare to alldatadiy) and followup directives to assist until you can subscribe.

Good luck with your task,

Dutch :thumbsup:

 

[samosali]

yes i have alldatadiy subscription and I checked what you proposed. I found some data but I must admit that I am not able to define which part(s) exactly causes the problem. I assume there is many different names for same part. So I am in my mechanic's hands. in addition, one man here said that the slide rings in the steering wheel and 4 tongues which slide on those rings are ONE spare part. if so, what is the MB part number?

I would appreciate much if you (or somebody else) are so good to list the part number and the name of a most possible culprit (4 rings in steering wheel and the corresponding contacts). thanks.

 

[samosali]

FYI: my car does not have clock spring under the steering wheel. There are just 6 contact tongues on springs and 4 sliding rings.

After disassembling the steering wheel the SRS light did not come on in 25 km drive which was the case before. It seems that there is small disturbance in wires or contact between tongues and sliding rings which was "repaired" by disassembling. However I do not believe that this is a permanent solution so now I am focused into replacing of sliding rings and maybe tongues too.

 

[Mercedes Mechanix]

FYI: my car does not have clock spring under the steering wheel. There are just 6 contact tongues on springs and 4 sliding rings.

After disassembling the steering wheel the SRS light did not come on in 25 km drive which was the case before. It seems that there is small disturbance in wires or contact between tongues and sliding rings which was "repaired" by disassembling. However I do not believe that this is a permanent solution so now I am focused into replacing of sliding rings and maybe tongues too.

Please recheck with your supplier to ensure the part you receive is for your vehicle:

Spring Assembly / Spiral Cable

Contact Switch assy
1405450366 Estimate of retail expenditure USA $69.00

Dietrich :thumbsup:

 

[Mercedes Mechanix]

Repai

FYI: my car does not have clock spring under the steering wheel. There are just 6 contact tongues on springs and 4 sliding rings.

After disassembling the steering wheel the SRS light did not come on in 25 km drive which was the case before. It seems that there is small disturbance in wires or contact between tongues and sliding rings which was "repaired" by disassembling. However I do not believe that this is a permanent solution so now I am focused into replacing of sliding rings and maybe tongues too.

Your disassembly and reassembly is exactly what the contacts are actually in need of. Oxidation will build up causing resistance to accumulate as well... thus, with higher resistance... it would appear that the contact face is open when made.

If reassembled and operating....

DO NOT FIX IT IF IT ISN"T BROKEN!​

If you want to have the new contacts on hand... then purchase the contact(s) and place them on the parts shelf in your garage... When you have another issue come up... your parts inventory will be right there ready to be installed! For now... just enjoy your Mercedes and take a day off!

Dietrich

 

[samosali]

I am on my own. My mechanic calculated 700 EUR for parts which is ca. $1,000. It seems that he really wishes his pool at the house.:crybaby2:

Another person sold me a clock spiral for 80 EUR which is actually not in my car, but we realized that later. Now he offers me used steering wheel with contact rings for this money (compensation).:crybaby2:

So the point is that people around me are not reliable or they do not know enough to maintain my car. Even if I do not see that promissed steering wheel with contact ring which is most probably not new, I have learnd a lot about the problem which is actually worth of 80 EUR.

The part number for a contact ring in the steering wheel is A000 460 00 49 (ca 200 EUR) if I am not wrong. If somebody can confirm this it would be fine.


Like you suggested the contact carbon for air bag is A140 545 03 66 (ca 40 EUR). These two should solve the problem if it will come on again.

I know how to replace carbon contact, I am just not sure if there is any trick in replacing the contact ring which is in the steering wheel. Thanks and best regards.

 

[samosali]

yesterday I removed the air bag and steering wheel as well. I think the reason for a SRS light ocassionally on was a graphite grease which was once in the past put on the sliding rings by my mechanic (it was also my idea).

The history; the steering wheel had a grinding noise therefore the mechanic rounded the contacts for air bag and horn and put some graphite grease on the sliding ring (my car does not have a clock spring plate).
After that the SRS light was on maybe once per month for several seconds in a first year. In last couple of months the SRS light was on in each drive for several times.

Therefore I polished all contacts and sliding rings in the steering wheel. Of course i removed the grease on contacts and rings during this procedure. HOVEWER, I did not remove the grease which was in the slots between 4 rings and around. So after polishing procedure i sprayed the thing with contact cleaner and lubrication for sliding contacts. After some days the SRS was on again .... so I started to conclude that the contacts and rings are bad and I must replace them.

But yesterday I found out that the grease (which was left in the slots) reacted with contact cleaner and became very liquid therefore it spread over the sliding rings, they were literally black and dirty!!! So despite the polishing I did not achieve anything because I did not remove the old grease out of the slots.

Now the rings and contacts are cleaned and polished, I used air gun and alcohol to remove old grease out of the area and I believe the SRS light will not come on again.

This is a typical example of how the technology influences the results and how we cannot trust to mechanics (or propose them our ideas).

 

[samosali]

FYI: only a day after the last post SRS light came on .... indeed not so many times like before the cleaning of contact ring. In addition, the noise when turning the steering wheel came back also.

Yesterday I replaced Air bag contacts A140 545 03 66 (ca 40 EUR). The old ones were ca. 2 mm shorter which significantly decreased the force with which they acted towards the contact ring. The new contacts are also softer if pressed into the housing and more rigid in all other directions. In other words the old contacts were really worn.

So far so good. the steering wheel is silent now, so I believe I solved the poblem.