1994 E420 ASR problems - PeachParts Mercedes-Benz Forum

fireman453 · #1 12-06-2008, 09:49 AM

I'm new to the MB world, just wanted a nice car so I bought 3--1988 300E, a 1972 350sl 2 dr sports coupe and a 1994 E420, its my favorite and causes me the most grief. I live in Ontario and as soon as the temp gets down around 0Celsius or 32 F for my american friends the car starts fine in the morning and as i start to drive down the road the asr light will come on and the car goes in to limp home mode. throw it into neutral and restart and it will be fine for a bit then does the same again. It will do this four or five times till the car warms right up and then it will be fine for the day. talked to the previous owner they tried replacing the stoplight switch as it does seem to happen sometimes when you step on the brake then other times when you let off the gas.......AAACCCCHHHHH!!!!! Help would be appreciated. Cheers from a northern MB lover

deanyel · #2 12-06-2008, 10:02 AM

Try a key word search - there are more threads on this subject than you can shake a stick at. One of the things you'll find is that you need to check the fault codes on the 38 pin connector. Just for the record an E420 is one of the best cars MB ever built and would easily be the least trouble of the three if it didn't have ASR, which is in the running for the most troubled automotive system ever made.

Arthur Dalton · #3 12-06-2008, 02:12 PM

Check tire psi...and sizing.

fireman453 · #4 12-09-2008, 03:53 PM

bump it up

Arthur Dalton · #5 12-09-2008, 04:01 PM

Did you check ?????????

deanyel · #6 12-09-2008, 05:03 PM

Tire pressure and fault codes - let us know the codes you got, or that you didn't get any.

ARNOLDLewis · #7 12-09-2008, 06:28 PM

You need to see what code you have that is keeping the asr light on before we can resolve any thing.

EricSilver · #8 12-16-2008, 01:23 PM

Quote:

Originally Posted by fireman453

... as soon as the temp gets down around 0Celsius or 32 F for my american friends the car starts fine in the morning and as i start to drive down the road the asr light will come on and the car goes in to limp home mode. throw it into neutral and restart and it will be fine for a bit then does the same again. It will do this four or five times till the car warms right up and then it will be fine for the day.

Likely Culprit: Coolant Temperature Sensor (which affects idle speed control).

Some consistent behaviors I have observed with my car:

1.) When Re-starting the car, RPMs surge higher than normal. If it surges above 1100 or so, the ASR fault Will be triggered again. If it goes to around 1000, then slowly eases down, ASR Might be triggered. If on restart RPM cranks up to about 900 then immediately drops down to about 600, ASR fault will Not be triggered.

2.) When restarting, but before cranking, a relay “ping” can be heard from the vicinity of the rear center seat, where the fuel tank is. It sounds exactly like the relay that trips when the seat heaters are turned on, (except that sound is from the rear left).

3.) The ASR fault does not go away until coolant temp baselines at 80C-82C. The test I would use is to simply turn on the windshield defogger and watch the temp needle. If it drops below 80, coolant is not yet warm enough. If it lands on 80 or above, it is.

4.) After driving a short distance, with coolant still less than 82C, and I stop and do some shopping or other activity that takes longer than 10-15 minutes, when I come out and start the car, it will be just fine (because heat soak has warmed the sensor).

The brake switch itself is not the issue; removing your foot from the accelerator, and the subsequent drop in RPM before your foot touches the brake, is. Sensory input to the computer does not correspond to its set of "Known Acceptable Behaviors," so it triggers the ASR fault. Also, if on the first start of the morning, you rely on the car’s own traction and don’t touch the accelerator when backing out and moving forward, you will Not trip the ASR at all, even if you repeatedly apply the brakes. Only after you engage the accelerator, rev the engine, let up (or upshift) and RPMs drop down, is the ASR fault tripped.

The brake switch is not the culprit, but is nonetheless involved in the process -- “involved” because it can be a trigger for other events, and also applies an electrical load. For example:

At the threshold where the car is almost warmed up, but not fully warmed up, the ASR fault may or may not occur depending on whether or not you apply a substantial electrical load. In my experience, restarting the car when it was warmed up (but not fully warmed up), cleared the ASR light and everything behaved normally, unless I turned on the radio or A/C (or both) and hit the brakes, which tripped the ASR. The power draw is apparently interfering with or diminishing sensor output. After shutting off radio/AC, restarting, driving/idling a few moments, the coolant becomes fully warm, and additional electrical loads don’t have any impact (perhaps because the computer is no longer attempting to regulate idle speed?).

If you speak to the previous owner, he will likely tell you the problem first occurred on a sub-freezing day and progressively got worse. You may also notice the problem is worse if the car sits in the rain overnight.

david s poole · #9 12-16-2008, 02:27 PM

both of you need to check the switch in the accel pedal.those cars with v8 engine came with warning not to rev the engine under the hood but to use the pedal inside the car or you would set a fault code.those switches are getting old and i have replaced two recently for the same symptoms that you describe.cured the problems.

Arthur Dalton · #10 12-16-2008, 03:20 PM

ThA suspect is low voltage comdition...check the alt regulator and brushees...

GregoryV022 · #11 12-16-2008, 07:13 PM

i have the same problem with my E 300 wagon, what does it mean when the ASR light is on

deanyel · #12 12-16-2008, 09:01 PM

Having an ASR light means that your car has ASR and that you should sell it immediately. If you are still interested in knowing more try a search or check your owner's manual. Check you model also - there is no such thing as a E 300 wagon.