94 E 420 w/ ASR in Limp mode

[DD2021]

Hi all,

First off -- thanks! Long time fan of these forums and this is my first time posting. I could use some of the expertise here to track down a problem.

Problem/Symptoms: Like the title says, I've got a 1994 E 420 with ASR in limp mode. ASR light is on, car starts fine now, can shift gears no problem, but I'm not getting any power until I push the pedal about half way down (mechanical throttle linkage takes over). Car first went into limp mode when I was on a surface street here in Tucson several weeks ago. Cycling power didn't help, but I was able to shift the lever from D into 3 or 2 and limp mode went away. Haven't driven it since getting it home, but switching gears no longer helps.

Diagnostic Codes: Cleared all codes on pins 4, 6, 7, 8, 16, 17, 19, and 30 with an analog tester (simple LED) and these are the ones that are now popping up
Pin 6: code 30 - CAN data bus to EA/CC/ISC control module (N4/1), interrupted (I know from the forums that this one is here to stay and can be ignored)
Pin 7: code 3 -
EA/CC/ISC actuator (M16/1)
Reference potentiometer (M16/1r1)
Actual value potentiomter (M16/1r2)
Safety contact switch (M16/1s1)
Closed throttle position switch (M16/1s2)
Actuator motor (M16/1m1)
Magnetic clutch (M16/1k1)
Pin 19: code 6 - Idle speed control inoperative

Resolution steps: Saw the wires from the ETA were deteriorated and decided to tackle replacing them on my own. After opening up the ETA and rewiring, I reseated the ETA and replaced everything that it was in contact with -- a new gasket, rubber boot, and rubber hose -- and followed instructions in FSM after reinstalling (closed throttle position looks good and the linkage cable is positioned so that the lever and crank are aligned). I didn't get to test any of the components in the ETA, I just replaced the wiring. Checking the connections after soldering the wires to the PCB, I noticed pins 12 and 13 (top left and top middle connections on the PCB) had continuity between them and pins 4 and 11 (connected to the body of the ETA) also had continuity between them. Does anyone know if that sounds right? See attached photos for reference.

Pertinent info: Lower wire harness replaced beginning of 2019, upper harness replaced in beginning of 2021. Haven't checked neutral safety switch.

Help: Is there anything else I should be looking at right now? I'm afraid something else in the ETA is inoperative, but I don't have another unit on hand and would like to rule out easier fixes first.

Thanks!
-Christian

 

[gerryvz]

The other common cause of limp-home mode is the neutral safety switch. This is mounted on the driver's side of the transmission. Have you taken a look at this? Often, but not always, it will throw a code.

I recommend finding a used ETA (with a date code of 1998 or later) and putting it in to see if the problem disappears.

Also, has your upper wiring harness been replaced?

A relevant thread to read:

ETA OR Upper Wiring Harness ?? | M119 Engine

Hi all,, These codes come back all the time , what is the most Probably : ETA ? or Upper Wiring Harness ? or both ?? Codes : 096 Starter lock - out and reversing lamp switch S16/3 ( It was changed ) 048 Set value potentiometer , potentiometer monitoring M16/1r1 018 Magnets for...

www.500eboard.co

 

[DD2021]

Upper and lower wiring harness replaced. I'll check the NSS by following the How-To. That part is NLA, correct? Would the E-GAS module be something to consider?

 

[gsxr]

Christian,

Fantastic first post - you provided all the right info! Since you cleared all codes, rewired the ETA, and still have code 3 on the E-GAS... it seems that something inside the ETA is suspect. If you had access to a digital scanner (SDS with HHT-Win, for example) it would narrow down which of those items shown for code 3 is specifically at fault. All of the M16/xxx items are internal to the ETA.

Here is the schematic for the ETA internals that may help you test it further:

https://www.500eboard.co/forums/misc/Manuals/Servicev3.2/W124/w124CD1/Program/ETM/2430400.pdf

A replacement ETA may be needed, or sending yours out to Victor at RestoreYourMercedes for a rebuild. Used ones, even late-datecode, are somewhat of a gamble unless there's a way to figure out the approximate miles on the ETA. The internals can wear out with miles more than age. If you do buy used (i.e., from eBay) make sure there's a good return policy in case it's a dud.

NSS will typically store a fault code, and yes it's NLA. They can be tested / refurbished, search the forum for details. Swapping in another E-GAS would be worth a try if you have one, but based on the code 3, it's more likely to be ETA internals. I assume the throttle cable is not overly tight and has play at the end, and the ETA linkage rests against the idle stop.

BTW, welcome to the forum!