1995 E420 ASR + limp home mode - PeachParts Mercedes-Benz Forum

#1 05-31-2002, 11:28 PM

Been lurking for many years now and learning a lot. Fantastic community, probably the best of its kind on the net. Thanks to the webmasters and moderators!

Well, the time has come for me to ask for help. I've seen several posts from Mercedes owners who have this problem: cruising at highway speeds ~70MPH after about 30 minutes ASR light comes on and car goes into limp mode. Turning car off then on corrects the problem. Also, as a side note, engine light has been on for over a year, but no other symptoms. The ASR and limp mode happened once over a year ago and I thought it was a fluke. But now for the last month it has happened four times.

I'm using a local shop and they hooked my car to an Alldata diagnostic system. The readings were as follows:

17,18
Test scope: Serial data bus (CAN)
Possible causes: Data line, DI control module (N1/3)

They reset the computer, it faulted (engine light on) and got the same readings again.

They tested the data line, it passed. They say now, its the computer. Replacement > $2K.

Are they on the right track? I saw that other lucky owners on this forum were able to fix the problem inexpensively by replacing:
- Transmission shift position sensor
- Brake light switch
- Over Voltage Relay

Has anyone had success by replacing the fuel actuator?
Is the Alldata system reliable?
Will a factory shop have better diagnostic equipment?
Is it worth trying the three above options and if so, which choice is the most promising.

Thanks!
Walter

Gilly · #2 05-31-2002, 11:36 PM

By far the most common reason for failure is the actuator (throttle motor) itself, especially when it only seems to happen hot. If it happens cold, the switches for the system should be checked with actual values, and you may want to have this checked anyways. make sure a couple base gaskets are ordered as well, I don't believe they are included, and it helps to have an extra one, it's really tough to get this in right. Also the breather hose from the throttle motor to the valve cover should be replaced, they get really stiff from all the heat in there, really cooks them, and that makes it tougher to replace the throttle motor.
Gilly

#3 06-01-2002, 10:20 AM

Thanks for the response Dan.

Even though the Alldata system points to a bad computer (DI Control Module), you think its the throttle actuator. How can that be confirmed short of trying one out? Are there any tests that can be performed or is trial and error the only way?

Walter

stevebfl · #4 06-01-2002, 10:50 AM

As to Alldata, it is a data system not a diagnostic system.

Your tech has used some method to talk to the car but without a code book I can't tell what he talked to. Since you were worried about ASR, I presume the codes are from there.

If there is concern that the DI controller (which one there are two) has a problem it should be consulted. ASR is the opposite of ABS, the system is looking for wheels that are accelerating faster than the others (instead of slower as in ABS). When faced with the wheel that is loosing traction the system aplies brakes on the offending wheel and reduces torque. It reduces torque by backing off timing (thus the need to talk to DIs) and reducing throttle.

Any activity that is not plausible will put the system in a safety mode, including limp home. All systems involved should be scanned and any codes must be evaluated. I almost always throw out codes saying a control unit is bad. Bad control units are almost always lack of communications and usually because they have shut-down for one reason or another.

Dan is right about the statistical nature of the solution to these problems: usually in the throttle assy. Harness problems also can get involved.

To judge a controller bad because no other problem exists is only scientific if the symptom exists while all tests show negative. Since the fault is intermittant no direct diagnostics will work.

#5 06-01-2002, 11:50 AM

I have a 94 E420, and the first time my check engine light came on, MB said I needed a new computer also. Evenutally, it was corrected with the wiring harness for free by MB after I learned about these problems through this forum. Check the other threads on shop forum regarding wiring harness, and have MB or an independent inspect your wiring harness. It is a good place to start. I might have replaced the expensive computer also when there was no need. I had about 85,000 miles on the car at the time.

You're right, these moderators know what they are talking about. They helped me too.

Gilly · #6 06-01-2002, 10:27 PM

OK, here's the deal. I've never personally had to do a harness on a 119 engine before. I have heard others say they have, even here on this thread. My problems with harnesses have been pretty limited to 104 engines, from the first year of SFI (92?) up to 94, maybe a 95 or two. And with the 104's anyways, sometimes you'll have a driveability concern, but usually just check engine lights, and usually those have been related to EGR or AIR injection switch-over valves screwing up due to the broken insulation. But I don't admit about "knowing it all", so it's a definite possibility you can keep in mind.
If you can wait, I wouldn't mind looking at the info I have at work for these codes. Just so we're on the right track, the ONLY pertinent trouble codes are 17 and 18, and I am kind of assuming the codes are in the EA (electronic accelerator) control module. You don't have ANY codes in either HFM (engine control module) or DM (diagnostic module)?
I assume you have already paid for diagnosis. You could always say you'll go for the control module, and you'll pay for it if the car is definitely FIXED. If it's happened 4 times in the last month, tell then you'll pay for it if it goes 2 or 3 weeks without a fail. If it fails again, it's THEIR control module. How's that for diplomacy?
Gilly

#7 06-01-2002, 11:20 PM

Dan,

I can definitely wait for you to check at work. I was going to have my mechanic replace the OVR Monday. My car has 90K miles and it's probably a good thing to do in any event, but it probably won't fix the ASR problem. I'll mention the wiring harness to him and see what he thinks.

I don't really know what the HFM (engine control module) or DM (diagnostic module) are but I'll mention them to the tech as well.

The complete details of the test they did are:

Code: 17,18
Test Connection: N3/1
- +
L--( <--- Ohms --> )--H

Test Condition: Ignition: OFF
Remove contact module or N3/1 and measure resistance directly at CAN connector for LH-SFI control module

Nominal Value: 115-125 Ohms

Possible Cause/Remedy:
Data line,DI control module (*N1/3)

There is a footnote: The DTC "18" can be displayed on vehicles up to 7/91 even if no fault exists.

Thanks!

#8 06-08-2002, 12:16 PM

Problem solved! And it cost me $16.00.

The post from Steve Brotherton had the following sentence, "Any activity that is not plausible will put the system in a safety mode, including limp home". A few months ago I put a little air in one of the tires that looked a bit low. At the time, I did not have a tire pressure guage nor did the gas station's air pump. So I just pumped in a bit of air and went on my way. Last weekend I went to Sears auto center and picked up one of those fancy tire pressure guages with the digital readout for $16.00. I checked the tire pressure: right front 39 lbs., left front 31 lbs. I then drove to a service center and adjusted the tire pressure according to the stickers inside the door, 29 front, 36 back. I added 3lbs to each because the tires were hot.

This past week I drove from NJ to Boston and back, about 500 miles, and the car never went into limp home mode! Not once. Problem solved!

I suppose that after driving at 70MPH for a sufficent time, the tire's diameter must have changed sufficiently to change the speed of rotation. The difference must have put the ASR into safety mode.

The engine light still comes on and stays on, but now I know its not related to my ASR problem. I don't know if I will try to fix it, but the wiring harness, if not too expensive, may be worth trying. But its good to know that I won't be needing a throttle actuator, a new control module and that my $$ will remain safely in my bank account for now.

Thank you Dan, Steve and everyone else for your help.

Walter

Gilly · #9 06-08-2002, 09:40 PM

Walter:
Glad to hear it's going well.
Sorry I never did get back to you in regards to the codes, just got people coming out of the woodwork for business lately, kind of caught me off-guard.
Gilly