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Discussion Starter #1
Ive read a bit here on the forums about limp-home mode. My problem seems a bit, different though.

1994 S420 AMG. 18 inch AMG rims, 255/45-zr-18 tires

Here's what it does.. Reverse: i have full acceleration
Drive: full acceleration for a second or two, then no response from accelerator until about half way to the floor.

Now, ive read a few threads about this problem, but, the threads i have read all speak of this being some sort of limp mode in which you dont get past second gear. My S420 rans through all of the gears BUT doesnt seem to have a passing gear.

It smells like a wheel sensor, but which one? are there 4 of the flippin things?

I also thought that the tire sizes may have something to do with it, but would prefer to know for sure before dropping over $800 on a fix that may, or may not work.

One thing is for sure, the car has 100% of its accelerator pedal response until the car rolls forward a couple feet, after that, its 50%
 

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Ive read a bit here on the forums about limp-home mode. My problem seems a bit, different though.

1994 S420 AMG. 18 inch AMG rims, 255/45-zr-18 tires

Here's what it does.. Reverse: i have full acceleration
Drive: full acceleration for a second or two, then no response from accelerator until about half way to the floor.

Now, ive read a few threads about this problem, but, the threads i have read all speak of this being some sort of limp mode in which you dont get past second gear. My S420 rans through all of the gears BUT doesnt seem to have a passing gear.

It smells like a wheel sensor, but which one? are there 4 of the flippin things?

I also thought that the tire sizes may have something to do with it, but would prefer to know for sure before dropping over $800 on a fix that may, or may not work.

One thing is for sure, the car has 100% of its accelerator pedal response until the car rolls forward a couple feet, after that, its 50%
just found out that after one hundred thousand kms your map sensor an o2 sensors should be changed cause after this long of wear they can alot of the time give out false reading!!
 

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I would unplug the MAF and try the car, this is nothing to do with tyres or vacuum leaks
 

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When the power output from the engine is down, the gearbox may not know what to do and it will often just lock up in second gear and many think that they have a gearbox fault, the name alone really spells this out "Torque converter" when the output from the engine is down, it is the torque that is down.

This must not be confused with the electro plate faults on the 06-06 onwards cars, these speed plates often fail leaving the car only shifting to 2nd.
 

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Do your ASR ABS lights come on? If not, have they been disconnected? To be sure they haven't when you put the key in position 2 all dash lights should be on.
This to me sounds like limp mode. Give us more info so we could help you. I struggled with limp mode on and off for almost two years.
 

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Discussion Starter #6
All lights come on when key in position 2 except....
ASR
Check Engine
and High Beam Headlight indicator...

seems some indicators have been disconnected eh?
 

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All lights come on when key in position 2 except....
ASR
Check Engine
and High Beam Headlight indicator...

seems some indicators have been disconnected eh?
This is another thought if no ASR lamp, but surely the triangle in the dial will flash if it is kicking in, or has that lamp been removed as well, take it for a drive and try and kick the rear end out when safe to do so
 

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Discussion Starter #8
A couple of notes. I pulled the mass air flow connector from throttle body (big round black screw-in connector), car ran like crap lol.

Had the rotors turned on the back today, had what looked like wheel sensors. On the passenger side it looked intact, bolted to the back of the wheen assembly and had a short cable that went to the brake caliper. Seems like a brake pad wear sensor. That cable from the sensor to the caliper, was missing from the sensor on the drivers side of the car.

Could that be the culprit?
 

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Discussion Starter #9
Another update, checked the cool little "blinky-light" DTC diagnostics box under the hood, got the following sustained DTC codes (yea, i cleared them and read them several times after driving it around a bit)

Code 6 : Idle Speed Control Inoperative
Code 18: Adjustable Camshaft timing solenoid open/short circuit
Code 19: Fuel Injector open/short or self-adaptation in LH-SFI control module (N3/1) at limit

Code 26: Upshift Delay 1 to 2

ok.... im confused lol
 

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You have a speed sensor 19 on both front wheels
 

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Discussion Starter #11
Wouldnt a bad wheel sensor throw a fault code? the only codes i get are shown below.

Another update, checked the cool little "blinky-light" DTC diagnostics box under the hood, got the following sustained DTC codes (yea, i cleared them and read them several times after driving it around a bit)

Code 6 : Idle Speed Control Inoperative
Code 18: Adjustable Camshaft timing solenoid open/short circuit
Code 19: Fuel Injector open/short or self-adaptation in LH-SFI control module (N3/1) at limit

Code 26: Upshift Delay 1 to 2

ok.... im confused lol
 

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Discussion Starter #13
I dont think i have to, i dont use a home made diagnostic code reader like some guys here use, nor do i have access to a store bought one, my S420 has a built-in diagnostic reader thats beside the computers on the passenger side of the car by the firewall. (the infamous "battery in trunk" box)

I follow a procedure and it'll blink the codes at me. Unless im supposed to short pins on the diagnistic port to access different parts of self diagnostics program, i think im following the right procedure.

*shrug*
 

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Discussion Starter #14
good god thats a huge pdf, may take me a while to sort through it lol, thank you, its about the most comprehensive fault code manual ive seen thusfar.
 

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Watch the 9 minute video in the top left of this page.

Mercedes throttle body rewire

Victor describes the operation of the electronic throttle body in the same vintage M119 engine. The real important stuff starts at 2:00. Notice the part where he plugs in the throttle body then operates the throttle cable connection, and the throttle plate starts to respond then releases. The car has gone into limp home mode. Why? Because there is a switch at the gas pedal that tells the car that the pedal is being pressed by the driver. If the pedal hasn't been pressed, but the throttle is receiving inputs as if the pedal has been pressed (Victor operating the cable lever on the throttle body), then the car thinks something is very wrong and shuts the throttle body down, putting it into limp home mode. It's a fail-safe mechanism to prevent a throttle run-away condition. There was a very recent discussion about this switch in a thread by bradscooters. This sounds like the situation you're facing. I don't know that the problem is the switch. Could be that the switch is working fine, but the throttle body isn't (possibly more likely). What is the condition of the throttle body wiring? The wiring is the point of Victor's video. He has replaced the wiring in that throttle body to allow it to function again. If you've got bad wiring, consider sending the throttle body to Victor.

Brett
 

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Discussion Starter #16
I thought the TB wiring may have been the problem too, but one thing tells me it likely isnt. If it was the throttle body, wouldnt it go into limp mode before the vehicle is in gear? It will rev up wildly with 100% of the accelerator. But if i put the car in drive and take off it looses half of the accelerator within a second or two. "only" happens when car is in motion. If i back the car up, put it in drive, then stomp on the accelerator it will almost put me through the seat with 100% pedal response.

Smells like a wheel sensor. anyone know if the back wheel sensors with the break wear sensor can be a cuplrit, as i said earlier, the drivers side rear brake sensor doesnt have a cable. the sensor is there, but the cable (think bicycle brake cable) that goes from the sensor to the brake caliper is missing? I presume thats not correct.

If the brake wear sensors can be the cuplrit, its likely the problem.
 

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I thought the TB wiring may have been the problem too, but one thing tells me it likely isnt. If it was the throttle body, wouldnt it go into limp mode before the vehicle is in gear? It will rev up wildly with 100% of the accelerator. But if i put the car in drive and take off it looses half of the accelerator within a second or two. "only" happens when car is in motion. If i back the car up, put it in drive, then stomp on the accelerator it will almost put me through the seat with 100% pedal response.

Smells like a wheel sensor. anyone know if the back wheel sensors with the break wear sensor can be a cuplrit, as i said earlier, the drivers side rear brake sensor doesnt have a cable. the sensor is there, but the cable (think bicycle brake cable) that goes from the sensor to the brake caliper is missing? I presume thats not correct.

If the brake wear sensors can be the cuplrit, its likely the problem.
Yeah, I think you are right. I would expect limp home mode while in park if it is this throttle position sensor mismatch. In the video, the car goes into limp home mode, and obviously, it is in park.

I'm not familiar with the on-board blinker. It was only on a limited run of cars... maybe only 1994 model year or something like that. If you search relevant terms, you may get more info on it.

The codes you're giving are only engine control unit related codes. You are not getting codes from the other system computers (like the ABS/ASR system, transmission, etc., assuming there are codes to be read). To access codes from other computers, you use the home-brew blinker box and connect the pins to different sockets in the 38-pin connector. With regard to the on-board blinker, maybe it only reports from the ECU... I don't know. I think it's not a case of codes not being there. It's a case of you not getting to the computers to read the fault codes, such as possible ASR fault codes. Maybe there are speed sensor faults stored in the ASR computer.

Have you only recently acquired the car? Or, have the dash warning lamps been inoperable for a long time? I'd get fresh bulbs in there.

Brake wear sensors are irrelevant to this issue. They literally only light the dash brake pad wear lamp.

And, I'd at least inspect the wiring to your throttle body.

Brett
 

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Discussion Starter #18
Brett, i just got the car a couple of months ago, previous owner didnt take care of it. Thusfar, ive fixed most of the issues. Had the oil changes in it a couple of days ago, the filter turned to mush in the mechanics hands lol. Its been quite an uphill battle to get this car back to acceptable mechanical condition.

I inspected the Throttle body wiring best i could without removal of the instake, wiring looks ok at the points i checked BUT i do get a fault that an injector wire is shorting. Other stuff in the harness is throwing fault codes too such as code 18 for camshaft sensor. Just for good measure, i'll likely replace everything that "can" go wrong before it has a chance to mess up.

I purchased this car with the mentality that i dont care what it cost to restore. I paid chickenfeed for it and what the hell, its mine ya know? No loans, nothing but my cash and my personality behind it. I figure i'll restore it to as new of condition as possible over time and as cashflow permits. I'll likely have 10-15K into a 5K bluebooked car, but im not restoring it for resale. I have a true blue appreciation for the vehicle. wish me luck eh? :D

I'll send it to the local MB gurus and check fault codes, they have a scanner with the adapter for it, perhaps it will tell more.

Thanks for all responses to this thread, i need all the help i can get.
 

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Brett, i just got the car a couple of months ago, previous owner didnt take care of it. Thusfar, ive fixed most of the issues. Had the oil changes in it a couple of days ago, the filter turned to mush in the mechanics hands lol. Its been quite an uphill battle to get this car back to acceptable mechanical condition.

I inspected the Throttle body wiring best i could without removal of the instake, wiring looks ok at the points i checked BUT i do get a fault that an injector wire is shorting. Other stuff in the harness is throwing fault codes too such as code 18 for camshaft sensor. Just for good measure, i'll likely replace everything that "can" go wrong before it has a chance to mess up.

I purchased this car with the mentality that i dont care what it cost to restore. I paid chickenfeed for it and what the hell, its mine ya know? No loans, nothing but my cash and my personality behind it. I figure i'll restore it to as new of condition as possible over time and as cashflow permits. I'll likely have 10-15K into a 5K bluebooked car, but im not restoring it for resale. I have a true blue appreciation for the vehicle. wish me luck eh? :D

I'll send it to the local MB gurus and check fault codes, they have a scanner with the adapter for it, perhaps it will tell more.

Thanks for all responses to this thread, i need all the help i can get.
JJRAGE, I see that you are in Texas - I'm in Houston and would happily read your car via DAS - no fee (if you're local!)
 
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