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W163 W202 W203 W246 MB100D
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Discussion Starter #1 (Edited)
Starting post below to share in case anyone else had or having similar issue with their W163 and might be able to help.
The closest discussion I found is in the SLK section

I have a 2001 ML320 with code (from icarsoft) P202E - [8] M16/6 (Throttle valve actuator) : Deflection of throttle valve (P0120) - photo below

The symptoms I am observing:
  • 9 out of 10 times on first start (car parked for 12h or overnight), BAS/ESP light is on (far left 1 light only) and rough idle, no power or limited, I believe this is "limp" mode , if you leave it long enough, the CEL gets triggered too
  • only seems to happen only on the first couple start ups of the day or until engine warms up a bit, once it goes away (from 2nd to nth start), the whole day its fine, CEL disappears too as you keep starting the vehicle
  • when the issue happens (only on first or so start up), I seem to have some success by pumping on the throttle pedal a few times before restarting or maybe when the engine has fairly warmed up in limp mode (so I am not 100% sure if its faulty pedal sensor or engine just warmed up and "cured" an electrical issue somewhere)
  • NOTE: The problem at the moment ALWAYS go away either by warming it up (wait 3-5minutes) or restarting and restarting 2x-10x until no BAS/ESP light comes up, doesn't reoccur until car is stationary again for a long time (whole day/overnight)
what I have tried to date:
  • replaced pedal position sensor (but I only got a used part) result: same, issue still occurs, I may have to try a get a new one later if my latest fix try does not do it
  • cleaned throttle body result: same, it was quite difficult and I could't really see how clean the placement was quite difficult to reach, but I'm quite sure its cleaner than before
  • throttle reset procedure
  • cleaned MAF - I was thinking this issue may have first occurred after I cleaned the MAF few months ago, so today I cleaned the MAF again, cleaned MAF connectors, reconnected etc
  • cleaned TPS electrical connector from outside - found the TPS electrical connector near the throttle body with lots of black soot around similar to what I have seen from throttle body (but not sure where its coming from as its in the back and I can't really see it), so I cleaned it as much as I can with electrical cleaner to get rid of the oil/soot and some papertowel and tried to plug/unplug but unable at that point, move the wires etc (just suspecting the oil may be impacting the sensor readings but when engine starts, this gets shaken off and returns to normal)
I have done the last 2 points earlier today, so I am on observation mode next few days if issue still occurs. will post what I find.I also plan to graph the TPS Circuit A and B if I can with my current scanner.

thanks to anyone who maybe able to help.

2643167


dash displaying BAS/ESP light:
2643171
 

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Discussion Starter #2
update

my last 2 points above did not fix it, I started it for 2 days and same issue, but again goes away when restarted after engine has warmed up, even without pumping on the pedal as I used to that I thought fixes it.

while the BAS/ESP light is on (problem is active) - did try 2 things

using a generic scanner (ELM327), the throttle response is not responding on the display - see below, its stuck at 6.3% throttle response even when I was depressing the throttle pedal, this changed when the issue went away (engine warmed up)
2643168



I also tried iCarsoft but this time the engine I believe has warmed up enough that the issue already went away but discovered that you can use icarsoft to read live data for signal 1 and 2 from the electronic accelerator system - photos below
will try again tomorrow! and read values before first start of the day and see values as issue is occurring

at idle:

pedal signal 1+2 is roughly 0.5v total
throttle valve signal 1+2 is exactly 5V
2643169


with throttle fully depressed (engine off):
pedal signal 1+2 is roughly 6v total - not sure if this is normal?? - but never had issue once it issue goes away so I'm assuming this is ok
throttle valve signal 1+2 is roughly 5V
2643170




I also checked via icarsoft scanner if the brake pedal sensor is working, there is a live data read that shows if its ON or OFF and it seems to worked fine - so that is not my issue.

try again tomorrow or next few days...
 

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If you have BAS/ESP warning on why there is no scan from traction systems module?
Check if battery voltage does not dip below 10V on startup.
In engine control module, actual values check if throttle stop is learned.

Don't run two parallel threads on same issue. ;)
 
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Discussion Starter #4
thanks for the response Witek_M,
will try to stay in this thread for this problem :)

i've tried to include all info below

re no traction system scan - you're right
I was actually reading the manual yesterday hoping to get a clue on BAS/ESP malfunction lamp and thought I will read those modules today (but I wasn't able to get a reading of it and got distracted haha)
short story, I have issues accessing the electronic traction module, I get this "link error" approx 19 out 20 tries! not sure why - another mystery to me
2643199


after I saw your response, I tried and tried again and got in the module eventually! and lo and behold 3 historic faults stored

C1200 Brake light switch - not sure if this is intermittent, but will definitely test tomorrow (also see live readings below on this)
2643208


C1401 High Pressure Return Pump - I think this maybe from a previous issue I have solved month's ago and never seen again (all 3 error lights on the left appear when I reach 20km/h) - which I will try and share later
2643210


and C1022 which I am suspecting maybe the reason I oftentimes cannot access the traction control module - not sure what to do with this
2643211


to verify C1200 - went to live data
brake pedal not depressed
2643205


brake pedal depressed
2643207


re battery, dropped to 8.52v when I started but no limp mode at all, engine just started beautifully, no malfunction indicators
2643204




re throttle valve stop learned - YES
2643212



all faults cleared as of today, looking forward to live data tomorrow! happy to hear your thoughts and suggestions!
 

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Discussion Starter #5 (Edited)
update:
without starting the car, I just left it at ON position to just read values using scanner.

Found the M16/6 throttle body actuator values not responding even when I was stepping on the throttle

no throttle input (engine off) - Throttle Valve Signal 1 and 2 are at 0.80 and 4.20 respectively.
2643316



throttle fully depressed (engine off):
  • Throttle Valve Signal 1 and 2 are STILL at 0.80 and 4.20! (issue: one should have gone up and other one went down)
  • but the pedal voltage readings went up - so this seems to indicate its not the pedal sensor (error code is correct pointing to M16/6)
2643317



Few minutes later, with engine still not started, just cycled OFF then ON position, the throttle valve values start responding!!
I did pickup the fault code P0120 again due to the initial no response. so I cleared it
And as expected when I started the car, no ESP/BAS light and no CEL - all good. seems I don't even have to start the car, just switch it on for few minutes before starting and it will be good!

Normal values for
throttle fully depressed (engine off) and throttle valve values responding depending on pedal input
2643319

wave for 023 M16/6 - TVA signal 1 - responding ok at this point
2643318



so just leaving the electrics running seems to fix it too.
Now thinking what next step to do....

1) replace throttle body which I absolutely want to avoid unless necessary, I find it challenging working on something at the back of the engine and you can't really see it! - I guess unless the problem does not go away

2) also thinking how do these values get to the scanner, I assume it's read from Throttle body to ECU to OBDport to scanner - is there a chance ECU is faulty? thinking of a reset, like remove battery and leave overnight

out of ideas as of now - looking for anyone's thoughts / input, thanks all!
 

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If battery voltage can drop to 8.5 volts, that's a clue right there.

I'd make 100% sure to fully charge with a proper smart charger (if lead acid fill with distilled water til plates covered)

Then Load test to make sure it can stay strong once load applied.

Should never drop below 10 volts under any circumstance.

If need a new battery use the AGM type for best performance & durability.

I got my Ever Start AGM for like $139 at Wally Mart

Hope this helps some - David in Texas
 

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Discussion Starter #7 (Edited)
ok thanks for the input David, I will give it a charge using one of those noco chargers
but im thinking this is probably not the root cause as battery really sounds strong when cranking it, 5-10x starts and still strong. battery is 2yrs old, not used much and I sometimes have it charged when not in use.
also, the last test it never dipped below 10v because I never started it, just left in ON position, throttle valve readings weren't responding initially but then eventually worked when
update: switched back off then on , then it works

thinking the butterfly valve doesn't open is the issue (initially), because I also observed I get 2 "over enrichment at idle" error codes (P2017-001/P0171 and P2086-001/P0174) when this P0121 happens .
1. either ECM told it to open but it didn't (throttle motor issue or stuck)
2. or ECM didn't tell it to open (ECM issue or some precondition not met / error encountered)
3. or ECM told it to open but it never got the message (wiring issue)
4. unlikely but - it could also be it actually opened but sensor didn't report it (I say unlikely because I see the enrichment codes above).

is this thinking sound? regards.
 

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Discussion Starter #8 (Edited)
update today:

  • charged the battery overnight with a smart charger, issue still occurred (bas/esp light on, limp mode, p0121 code until restarted)
  • will review freeze frame data from scanner and see if anything looks odd or if something else triggers the P0121, throttle valve could be deliberately disabled by ECM because of another pre-condition/error, any ideas where else to look? (MAF? MAP? etc). note: Both signal 1 and 2 are stuck until cycled.
  • switching off then on /cycling the ignition fixes it, maybe 1x or 2x or 3x, not just by leaving it ON
will having SDS help? (will I see more data than I currently see?) thanks.

thank you, any help appreciated.
 

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I would go back to the TPS and check to make sure the wires are firmly connected and not damaged, perhaps even replace it (cheap and easy enough to do).
 

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Discussion Starter #10 (Edited)
thanks Khomer, will try again to move the wiring, unplug clean plug and report back.

at the moment, I'm close to eliminate wiring as the rootcause, as it only happens on first start and never happens the rest of the day (if wiring issue, thinking movement/vibration is likely to trigger it again when in use)

which leads me to believe it must be some kind of

1) mechanical issue, getting stuck, but it eventually gets freed (like motor stuck but if left with current moves eventually) - I may have to replace the TVA if next point below does not lead me anywhere.

2) some other sensor is intermittent so ECM deliberately freezes the throttle valve (the faulty sensor eventually works after it gets current supplied for a minute or so - maybe MAF or something), this might be a fail safe strategy of mercedes? anyone familiar how it is programmed (what ECM checks as pre-conditions)? this maybe unlikely given there are no other fault codes.
I wish ECM has a log somewhere! can SDS read this?
 

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update today:

  • charged the battery overnight with a smart charger, issue still occurred (bas/esp light on, limp mode, p0121 code until restarted)
  • will review freeze frame data from scanner and see if anything looks odd or if something else triggers the P0121, throttle valve could be deliberately disabled by ECM because of another pre-condition/error, any ideas where else to look? (MAF? MAP? etc). note: Both signal 1 and 2 are stuck until cycled.
  • switching off then on /cycling the ignition fixes it, maybe 1x or 2x or 3x, not just by leaving it ON
will having SDS help? (will I see more data than I currently see?) thanks.

thank you, any help appreciated.
When you first turn key on ME performs self test then comprehensive test of all connected components. Part of that test is throttle actuator. It goes to WOT and back to idle position. If current needed to drive motor goes above 6A throttle actuator is de-energized.
 

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Discussion Starter #12
When you first turn key on ME performs self test then comprehensive test of all connected components. Part of that test is throttle actuator. It goes to WOT and back to idle position. If current needed to drive motor goes above 6A throttle actuator is de-energized.
thanks Witek_M, this makes sense!!! exacly the specs I need ---> #5 fault setting conditions

before I order a new or maybe used throttle valve,
1. I'll have another go at cleaning the valve in case something sticky is holding the butterfly valve if left overnight
2. and cleaning all connectors (at throttle valve and at ECM area) to ensure resistance doesn't go higher than what it should be, not much I can do with the 20yr old wires, I think these increase in resistance as it ages (or get new wiring if I think I can replace them easily) - cant really see anything back there

ill just wait for warmer days, winter here, no snow but still cold outside

cheers!
 

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thanks Witek_M, this makes sense!!! exacly the specs I need ---> #5 fault setting conditions

before I order a new or maybe used throttle valve,
1. I'll have another go at cleaning the valve in case something sticky is holding the butterfly valve if left overnight
2. and cleaning all connectors (at throttle valve and at ECM area) to ensure resistance doesn't go higher than what it should be, not much I can do with the 20yr old wires, I think these increase in resistance as it ages (or get new wiring if I think I can replace them easily) - cant really see anything back there

ill just wait for warmer days, winter here, no snow but still cold outside

cheers!
Do you have trusted volt meter and set of back probes?

See if you can find it locally.
 

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Discussion Starter #16 (Edited)
thanks will order this, will be a good set to have, also good its amazon prime so can get via free delivery outside US

Also, a quick question on pedal position sensor, I know this is not the issue based on testing (just thinking if this is or will be problem but likely not)
  • my previous pedal position sensor has a marking of 1.0 in big font
  • the replacement part I got I believe has 1.2 - Any idea what this means? does it matter? same part number A012-542-33-17. car currently has the one with 1.2 with no issues except for the intermittent issue posted on this discussion, which also happens when it had the 1.0 part installed. THANKS again.
2643864
 

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Discussion Starter #17
update today:
- Checked wiring connections again, all seem good and connected properly. unplug connectors, sprayed cleaner, wait to dry, reconnected - issue still there.

next:
- Will do 1 last clean on throttle valve (again) - try to clean whatever MIGHT be preventing it to do WOT within 0.5 secs if left overnight (I honestly think its inside the motor enclosure so likely this will not work)

if last cleaning fails, throttle valve will be replaced.
Looking at orig used part (50% cheaper but risk of having same issue) or new Bosch (preferred)

not very urgent as current workaround exists, cycling ON/OFF position couple of times before starting it up (this will make it do WOT couple times to loosen throttle and meet the 0.5sec test!!), eventually issue is gone and fine for rest of day
 
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