Dear Forum Gurus...

my e320 1995 wagon is in limb home mode! The RPM are limited to 1500 rpms and it idles at 1000rpm! I know everybody would say wiring harness - NO it is not it was replace... Next would be the OVP... NO it is new also...

The next ones would say read the error code! Here we goo... (YES I cleared the old ones!)

PIN 8 shows...
- 8 Idle speed control (ISC) system at upper or lower control stop or CC or EA indicates "limp
home" mode.

45 Fuel safety shut-off of electronic accelerator or cruise control active

Pin 14 shows...

2 EA/CC/ISC control module (N4/1) or Safety contact switch (M16/1s1) or Stop lamp
switch or Cruise control switch or Actual value potentiometer or Starter lock-out/back-up
lamp switch or engine speed signal or vehicle speed signal or closed throttle position
switch or safety relay in EA/CC/ISC control module

11 Closed throttle recognition signal to engine control module (HFM-SFI or Left LH-SFI)
Fuel safety shut-off to engine control module (HFM-SFI or left or right LH-SFI)

Now things get trickier! - Not knowing what to do I replaced the ETA! Mainly because in the manual there is a scenario described between a mismatch between the readings from the two potentiometers in the ETA if the cruise control is not activated...

HOWEVER I replaced the ETA and same story..

I will check the wiring next but what I noticed that the ETA seems to be operated at 5 V! This is highly unusual for a car electronic and would it point to the unit itself being shoot?

Has anybody one of these units laying around in the Nashville area so I could check it? Obviously it has to work and come out of a running car!

OR anybody with a scan tool which can read the sub codes!

ANY other suggestions?

Cheers,...

Back-probe the throttle position switch at the ECU harness to make sure it's getting the correct signals.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

I started to look into my problem further to see what causes my limb home mode! I want to get to the bottom of this if I can!

- I have the circuit diagram showing all the connections to the N4/1 control unit! It is not that bad the unit does not get that many inputs.

- I check all the cable going from N 4/1 to the throttle actuator - the are fine and no shorts for sure! THE ONLY SURPRISE was that the switch S1 in the throttle actuator has a very high resistance of about 1200 Ohms. The switch S2 in the throttle actuator has a couple of Ohms (THis is what I expected). However, I check on a working throttle actuator and get the same results. Confirmed by others... on the block..

- I check the connections to the main control module N 3/4 - They are fine!

- I check the function of the brake switch as well as the cruise control switch and they all work as they should!

- The other inputs are from the ABS unit and the A/C! I assume that the system would light up the ABS light if anything is wrong with the ABS unit! NO ABS light is on!

- I also think that the A/C would not be able to trigger the limb home mode...

- Also the voltages are supplied from the Overvoltage protection relay

NOW THE QUESTION ARISES WEATHER THE MODULE N 4/1 IS SHOOT! I HAVE A USED ONE COMING!

DO I MISS ANYTHING?

CAN ANY OTHER MODULE TRIGGER THE LIMP HOME MODE? - THE LIMP HOME MODE IS ONLY MENTIONED IF THE N#?$ UNIT DOES NOT GET VOLTAGES REPRESENTING THE POSITION OF POTENTIOMETER R1 AND R2 IN THE THROTTLE ACTUATOR FROM N 4/1!

I MUST HAVE MISSED SOMETHING!

MY CAR IS STILL IN THE LIMB HOME MODE!

WHAT CAUSES THE LIMB HOME MODE?

What on earth makes this so difficult to debug!

PLEASE get me out of the rain!

You have to be, at a minimum, smarter than the car. Ideally you will be smarter than the engineer who designed it, but again, as a minimum, smarter than the car. BUT! 1995 was quite a while ago.

__________________
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I heart post 95 models have all the error codes accessible and you can read them out EASILY! OR IS THIS A myth?

That car has very good diagnostic abilities!

You need a MB scanner to see the live data stream though.

Did you replace the neutral safety switch, code 96? or the brake lamp switch?

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
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Is there somebody in the Nashville area who could read my codes? (I have a blink code reader but can not get the subcodes... - is there a description of what pulse sequenced to sent the unit? I am pretty handy in microprocessor programming and am familiar with many communication protocol!)

I replaced the break switch but did not touch the safety neutral switch.

Thanks,

Franz