ASR Light - HELP M.B. DOC ! - PeachParts Mercedes-Benz Forum

silv500 · #1 12-13-2005, 08:00 AM

Hi , I have the ASR problem i have read so much about on this forum. I have a 1990 500sl and it has only recently developed this fault. The strange thing is, when i slightly adjust the slack out of the throttle cable, the light goes out and the car comes out of limp home mode. Sometimes it lasts for weeks, sometimes it needs more tweaking. recently this has stopped working and the asr stays on and in limp mode. With the cable adjusted even more, the car idles too high and seems to have a mind of its own in the rev range. However with careful adjusting i can get the asr mode off and the car idling right BUT as soon as i even breathe on the accel pedal, ASR ASR !!! aaargh.

My questions are these, if anyone can help :
I have read lots about people changing the brake switch - does this seem like a suggestion for me ( i'm not sure as the accel pedal touch relights the asr )
Also, i heard something about the OVR Over voltage relay ? Reason i ask is tha my car was jump started and i think thats where all this started.

Any help greatly appreciated, as my grin is now

mbdoc · #2 12-13-2005, 08:17 AM

THAT is one of the hardest systems to diagnose due to NO computer memory.

IF the system stays in limp mode then a pin to pin is required.

MOST common failure (beside the brake lamp switch) is the accelerator potientiometer!

silv500 · #3 12-13-2005, 08:54 AM

thanks for the quick reply.
is that the part that costs $1200 ? Just my luck !

what do you mean by a pin to pin ?

mbdoc · #4 12-13-2005, 10:56 AM

Pin to pin requires a volt/ohm meter & wiring info for that system. Basicly checking for correct signals to/from computer.

The potientiometer MB part number 000-540-14-17 lists for $ 695.

silv500 · #5 12-13-2005, 09:32 PM

Thanks MB doc.
Is that the large part described here ...as an electronic throttle actuator

http://pages.prodigy.net/jforgione/MB_asr.html
sorry for all the questions

deanyel · #6 12-14-2005, 12:05 AM

You have a 1990 500SL with ASR? That's strange. What country? Is your engine a 119.960?

JimF · #7 12-14-2005, 11:59 AM

Quote:

Originally Posted by silv500

Thanks MB doc.
Is that the large part described here ...as an electronic throttle actuator

http://pages.prodigy.net/jforgione/MB_asr.html
sorry for all the questions

You can build a homebrew code reader described in MENU#2. That will allow to read what the CFI module "thinks" is wrong. I would venture a guess that you may read DTC#10?

16 pin Diag Connector
Yellow: Read data from Pin 3
Power from Pin 16; Ground on Pin 1

DTC Readout Possible Cause of Failure
1 No fault found
2 Throttle position switch; wide-open throttle fault (WOT), signal faulty
3 Engine coolant temperature in CFI control module illogical
4 Air flow sensor position indicator potentiometer current illogical
5 Oxygen sensor signal illogical
6 Not used
7 TNA- signal (rpm) at CFI control module illogical
8 Altitude correction signal from ignition control module
9 Current to EHA is illogical
10 Throttle position switch; closed throttle position fault (idle)
11 Air injection system, open or short circuit
12 Absolute pressure values from ignition control module illogical
13 Intake air temperature illogical
14 Speed signal at CFI control module illogical
15 Not used
16 Exhaust gas recirculation switchover valve, open or short circuit
17 Oxygen sensor signal wire shorted to positive or ground
18 Current to idle control valve is illogical
19 Not used
20 Not used
21 Not used
22 Oxygen sensor heater voltage illogical
23 Short to positive in purge switchover valve circuit
24 Not used
25 Short circuit to positive in start valve circuit
26 Short circuit to positive in upshift delay solenoid valve circuit
27 Data exchange between CFI control module and ignition control module
28 Intermittent contact in engine coolant temperature sensor circuit
29 CFI and ignition control module reading different engine coolant temperature
30 Not used
31 Intermittent contact in engine coolant temperature sensor circuit
32 Not used
33 Not used
34 Engine coolant temperature read from ignition control module illogical

silv500 · #8 12-15-2005, 06:48 AM

thanks JimF, thats a good load of info, I appreciate your help. I will get onto your idea. However if i get fault 10, is that the same part to be replaced as MB doc suggested or is the position switch totally separate ?

....going no where fast,,especially in asr mode !

mbdoc · #9 12-15-2005, 08:03 AM

Code reading of the fuel system is a good IDEA, HOWEVER it won't help you at all in diagnosing your ASR problem! That is a stand alone system with NO diagnostic memory!

AGAIN that is one of the hardest systems to diagnose! YOU need a good technician with good info on that system!

HJHJ VAN EKERT · #10 01-07-2006, 08:07 PM

I am nearing the end of my wits with this problem on my 93 600SEC. Here is what I have done to try to correct it over the past 8 months (basically have not been able to drive it normally):
1. went to several reputable Mercedes mechanics, paid each time to have the codes read. None could pinpoint the exact cause, but each suggested starting with a thorough wire harness check.
2. I completely replaced both MAF harnesses, all the way to the bottom connectors in the module box, checked continuity on all these wires numerous times. The originals were in a very sorry state, just a bundle of bare copper strands with plastic powder around them.
3. Removed both ETA's, opened them and checked all wiring from boards=to=plugs, all good. These harnesses were new, having both been replaced previously. Connected both harness plugs, with the ETA's sitting on top of the engine, and started the engine ( it will actually run this way, but since there is a complete lack of MAF feedback, plus no throttle, the engine rpm will slowly increase to a point where I have to switch it off). The purpose of this exercise was to allow a visual verification of the ETA function by depressing the accellerator pedal with the engine running, and both ETA's are acting normally.
3. Each time the engine is started, with the ETA' mounted back in place (after clearing all error codes using my Trisco scanner), the engine runs fine and revs up normally, for about 20 seconds, at which point the ASR light comes on, and Limp Mode is active.
4. The error code is the same each time, the LHI module check shows a code 17 ("MAF sensor voltage high or low or open wire"), for the LEFT bank only, the right bank reads "normal" every time).
5. I tried a process of elimination, by first swapping the 2 LHI modules - still the error is on the left bank, indicating that the modules are not at fault.
6. I thought it must be the MAF sensor, bought a new one, no change. Swapped the MAF sensors left to right, still have the 17 error on the left bank only.
7. Checked and re-checked MAF harness to module box continuity, all good.

The problem persists, and I have no idea what to check next. I would love to drive this car, but it has been many months (actually, it did spend 2 of these months in the shop to have the transmission rebuilt - the infamous slow reverse engagement probem which results in a mass of ground up springs in the pan....but that is another story - this car seems to be blessed with all the possible problems that have been reported as common to this generation, including the sound system,the window closers, and the A/C evaporator....) It is the ultimate example of a love/hate relationship at this point.

I'd be extremely grateful for any suggestions.

JimF · #11 01-07-2006, 08:48 PM

You have done a very thorough and logical flow trying to fix the problem. There's not much one reading this can suggest other than trying to 'zero' in on the #17 DTC. Maybe there's is a connection problem "someplace" in the signal chain.

Don't know what else to say?

HJHJ VAN EKERT · #12 01-08-2006, 11:28 PM

Well, spent sunday afternoon and evening on further diagnosing. Here is what I did today:
I put the car on my Werther lift, and swapped the oxygen sensors. No change, it still fails on the left bank only, so that eliminates the O2 sensors.
Then I tried something different, started the car and kept it running at 1500-2000 rpm, with a few revups to 3-4k. I did notice that around 4000 to 4500 it starts bucking as if some kind of rev limiter is activating intermittently, which I do not think it should??? But anyway, as long as I kept the rpm's above 1500, the ASR light NEVER came on, even after 15-20 minutes running!!!
BUT as soon as I let it drop to normal idle, or anything below about 12-1300, the ASR light and limp mode come on within a few seconds....... If I restart the engine, the light is off again, but will come on as soon as I allow the engine to idle. Could it have something to do with the pedal position switch/sensor, or the cable adjustment????

myarmar · #13 01-08-2006, 11:55 PM

Harmen, what is your source for LH code 17 interpretation as "MAF sensor voltage high or low or open wire"?
In my 1992 code book it is " No data transmission from Electronic Accelerator Control Unit (N4/1)".
Mike

JimF · #14 01-09-2006, 12:35 AM

Quote:

Originally Posted by HJHJ VAN EKERT

Well, spent sunday afternoon and evening on further diagnosing. Here is what I did today:
. If I restart the engine, the light is off again, but will come on as soon as I allow the engine to idle.

Could it have something to do with the pedal position switch/sensor, or the cable adjustment????

I believe I had similar symptoms and it has to do with the comparison to the accelerator position (pot) as compared to the Ref Pot in the ETA.

In my case the "pot" was worn and had open/ohmic spots. If this occurs, then the positions are in conflict (don't match) which forces the LH mode.

In my car ('94), the "Diag Module" is used and a key code, DTC#6, "ISC inoperative" was added. That's MBs 'short' explanation for the above sentence and as a 'catch-all' for all kinds of Idle Speed Control (ISC) problems.

From what you describe, yours appears to be similar.

1991 560 SEC · #15 01-09-2006, 06:26 AM

Buckwheat, Raise your right hand.........Your other right hand