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Loss of Power when accelerating

34K views 47 replies 6 participants last post by  sparky1016 
#1 · (Edited)
A friend of mine(99 ML320 @150k miles) is experiencing sudden loss of power while accelerating. According to his description, after reaching around 40mph, ML would lose power completely. Seems like tapping brake pedal slightly a couple of times, returns to normal every time. This only happens when accelerating to enter highway speed with engine still not warmed up, and happens almost every morning. Driving on city streets for a while(10 minutes or so) prior to entering highway without any problem.

Checked this forum for "sudden power loss issues", found symptom is very similar to yaw rate sensor or lateral acceleration sensor problems, but no related codes are found.

Scan with Autel 802 resulted P0150 & 0155, don't think the cause of sudden power loss. Bank 2 before cat O2 sensor was replaced about a month ago with Bosch 13782, all new NGK 4696 with Kaylin wire set at the same time. The ML had been running fine after the repair.


Note he lives in rural poultry farm, found a rat couple nested under the hood, chewed up a few wires including one shown below, but the wires are not broken. Other damaged areas are not as bad as this one, don't see no chewed up vacuum hose either.

Help please!
 

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#2 · (Edited)
You need to do a careful inspection of what the rat family may have damaged while in residence. Once you have that covered tape them up or silicone them to prevent shorting. Since you don't say whether the scan prior to the current scan was cleaned I'd suggest you clear the codes and then drive the vehicle and attempt to duplicate the same symptoms. Then scan the vehicle for codes. Once you get the current codes post them and we'll see what we can shake down. Good luck.
 
#8 ·
Look through scanner manual how to retrieve freeze frame and how to read live data.

Values of interest are STST, LTFT, MAF, engine temperature.

Read about fuel trim here: https://www.obd-codes.com/faq/fuel-trims.php

Screenshot showing live data from my E320.
Thanks for the reply. I emailed to my friend to have the brake light checked while it's happening, waiting for his response. He's busy feeding of his 3000+ chickens every morning. I'll try to follow your instruction, when I go visit his farm in a couple of days.
 
#6 ·
Seems like tapping brake pedal slightly a couple of times, returns to normal every time. This only happens when accelerating to enter highway speed with engine still not warmed up, and happens almost every morning. Driving on city streets for a while(10 minutes or so) prior to entering highway without any problem.

/QUOTE]

Tell your friend to try and replicate the problem, but instead of stopping on the entrance ramp, pull over to the side and apply the brake only once for stopping, get out and see if your brake lights are on.

If so, a new Brake Light Sw. is needed
 
#12 ·
Just received confirmation that brake lights are working when pulled over during the same symptom happened. Does it confirm the BLS is not faulty? I can reinstall it if needed.

Forgot to mention, YELLOW TRIANGLE WARNING LIGHT LIT UP AND FLASHES when it happens.
I had the CEL cleared, codes erased 2 days ago, but CEL returned after the a few miles. I'll be at his chicken farm to scan for fresh codes.

Will look for live data for fuel trims, MAF and temperatures, etc readings and report back.
 
#23 ·
Indeed I misread and misinterpreted your instruction, wasn't aware of you're looking for sticking brake lights.




I don't know what you're thinking by above statement, I'm only trying to help this poor old man, whose idea of maintenance had been just oil change with Castrol non-synthetic oil every 10k miles or so, nothing else for 6 years since he bought this ML in 2011 with 90,000 miles, now 150k. He said he's been driving with CEL, BAS/ESP & ABS light on for 3-4 years which lit up when he was living in Alaska. (smog check is not required for registration here in rural Oregon). I convinced him to have all the fluids replenished, plugs and wires done, fixing badly leaking engine oil, chewed up air filter by resident rats . . . I didn't do any these work, only helped him with what's needed and where to buy the parts for good price, but someone else did the work for nominal labor charge, since he doesn't have any solid surface to safely raise the vehicle.

I spent some of my own money, own gas for many trips to his farm(6 miles one way) and taken him to mechanic in town(20+ miles one way) a few times not even counting my time. All these without any compensation other than a few dozen eggs from his farm(which I don't eat much).

I don't have much knowledge on automobiles, but he is far worse than myself, IMO, the reason I have been posting these, but I'll have him to read this forum and respond himself. I'm done with this nonsense.
 
#26 ·
The Yellow Warning Triangle signifies that there is a problem with the Traction Control System, ESP & 4-ETS. Brake related.

The two "P" codes have nothing to do with illuminating the Yellow Triangle.

What I believe is that the scanner/code reader you are using is not able to read "C" codes which relate to Traction Control System.
 
#27 · (Edited)
Thanks for your input, 43sqd.
The scanner used is AUTEL MD802 MaxiDiag Elite, able to read P, B, C, U codes. In fact, used it on this same friend's ML320, pulled C1200 code a couple of months back which led me to replace the BLS. After replacing BLS, erased the code and C1200 code is no longer present.

Brake light worked as it should (not lit when tested as the /!\ warning light flashed. The ML is able to slowly accelerate to highway speed, but almost always flashes at certain point. If it IS brake related problem, I should go ahead and order a new BLS, which may or may not fix the problem, but it's not terribly expensive. What do you think?

As a note, I did try re-installing the BLS, but no difference. Thanks again for your for help
 
#34 ·
Just a thought is the steering wheel straight. What I mean is on a straight road is the steering wheel level. It's like your steering angle sensor is out of alignment and once you get to a certain speed it thinks your cornering to fast. After turning the engine on try the lock to lock a view times. I'm not sure of the exact reset procedure but that works when the lights are eliminated. Has an alignment been done recently? They may of pulled the steering wheel of to align it straight not knowing any different.


Sent from my iPhone using Tapatalk
 
#35 ·
Hi Matt,

I didn't feel the steering wheel is off, I wasn't looking for this when driving, but it's hard to miss if the wheel isn't straight.

Yes, alignment had been done recently after front tie-rods replacement. I asked my friend to do the lock-to-lock a few times to reset the steering angle sensor, but the warning light only comes on when engine is cold, will check on that later. Thanks for your suggestion.
 
#37 ·
43sqd, as I described in post #1, my friend's ML had a "rat couple" did some wiring damage including the one image shown below. Please be specific in how to test relay, as there isn't a like one to swap. I do have a analog volt/ohm meter.

I am going over to my friend's place now to swap his relay with mine. Thanks!
 
#38 ·
Swapped K6 relay from my ML to my friend's ML, still had the same result. When speed reaches 30mph, warning light begin to flash. When speed drops to 26-27mph, light goes out. But once I tap brake pedal, no more warning light. Also, checked K6 relay with ohm meter, the reading between any two leads off the K6 relays resulted exactly the same between two relays.

Steering wheel feels pretty straight and level, tried to reset steering angle sensor by doing lock to lock a few times, the same result. Must have been the resident rat couple that did the wiring damage, sigh . . . Thanks.
 
#40 ·
There are at least 2 places of rodent damage I found, including one shown below. Continuity test shows it's not broken or doesn't seem to be shorted. The other place is on big bundle of wires located between fuse box(under hood) and fender. The outer casing was chewed, one of the wires showing bare wires, but doesn't seemed to be broken under close visual inspection. The area is very tight, unable to get my hands in, sprayed with flexible rubber.

Kept a cat around this area for a while, caught two rats, but other new ones keep showing up.
 

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#41 · (Edited)
Also, rat got into the air filter casing, found underside of the filter chewed up twice, prior to this flashing warning light showed up. The wire damage next to under hood fuse box was also discovered prior to warning light flashing.

My observation after driving the truck for a while, the ML drives like nothing had happened after light tapping on brake pedal when yellow warning light flashes. The yellow warning light stayed off until next driving cycle. Once the engine is off, wait for 10-15 seconds, then restarted, warning light comes back flashing.

The warning light starts flashing once the speed goes above 30 mph, when speed drops to 26-27 mph, goes out. But always comes back flashing when speed reaches 30 mph. Doing this repeatedly until brake pedal was depressed once and stays off until the next driving cycle.
 
#42 ·
The problem must be at the fuse box where you cannot get to. Every wire that goes to every module in the fuse box is in that large harness.

Traction Control, ECM, AAM wires are all bundled together. Nothing will correct itself until a thorough inspection is made.
 
#47 ·
Since you are getting Fuel Trim codes along with the ESP triangle lighting up, you must consider the fact that wires in the fuse box are touching.

And since this is happening at 27 mph, it is a safe assumption that wires from the ECU module (trim codes) are touching wires from the ESP module (triangle) in that the ESP function is not activated until 25MPH.
 

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