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Old 01-05-2008, 08:16 PM
Join Date: Dec 2007
Posts: 3
Default Engine check light DTC P0170 and P0173 fuel trim system malfunction

Hello there,

I have 98 E430 and it has check engine light with code p0100 (MAF), P0170 and P0173 fuel trim malfunction B1 and B2. The engine run good at idle speed at cold orhot (normal temp ~90c). Howerver if I drive forabout about15 min on the freeway (70 -80mph), the car suddently cannot accelerate; the speedomer dropped and the engine felt like starving fuel and jerk a lot. I checked the LTFT while it happened, theLTFT for bank1 and bank2were over 35. I replaced lots of parts but this car still have the same problem. Here are parts I replaced: MAF, Throttle actucator, intake flap switch over solenoid, O2, intake pipe, spark plugs, MAP sensor, fuel filter. I checked for leak, but vacuum reading is good. All parts I replaced are from dealer. I run out of idears. I suspected the ECM but not quite sure.Anyone have seen this problem?. Please help!
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Old 01-06-2008, 01:36 AM
Join Date: May 2007
Posts: 1,057
Default RE: Engine check light DTC P0170 and P0173 fuel trim system malfunction

The wire harness to the maf is either not sending power or is not making contact.Or you need to test the cats.Stop throwing parts at it at this point and I hate to say it you may be at a time when it needs to go to the shop,if you can't test the cats or the maf circuit.
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Old 01-06-2008, 11:06 PM
Senior Member
Join Date: Dec 2004
Posts: 2,409
Default RE: Engine check light DTC P0170 and P0173 fuel trim system malfunction


Your DTC's definitely point to a MAF issue.
The usual signature is just P0170/3 which is due to a LTFT above 30 which is a preset threshold value. Demonstrates deterioration in the MAF sensor/circuit resistance.

However the effect of the LTFT being above 30 will be to cause the engine to run weak under acceleration and thus cause a misfire.
The misfire is picked up by the crank sensor / ECU and causes the CEL to illuminate and possibly go into Limp Home (speed limited to circa 30 mph with jerkiness etc.) if the misfire is "bad".
You make no mention of DTC's indicating Misfire on one, or several cylinders!

The P0100 is a MAF circuit malfunction. The ECU cannot see the MAF so its surprising that you also get the P0170/3 DTC..

So the issue is why!

Most likely a faulty connector to the MAF.
Check connector pins have not backed out?
Check harness/wiring insulation all the way back to the ECU.
Sure you new ECU was Genuine MB in a sealed box and the correct Part No. (for instance... Not Diesel)

VERY unlikely the ECU is faulty however it has been known for oil or water to enter the ECU black box.
Is the electronics box / ECU dry?
Any sign of corrosion on the connector pins / circuit board.

As Ohlord states throwing parts at an MB (or any modern car) is NOT the way to correct a problem unless you have deep pockets. Cost of repair (genuine parts) so far??

You are the first guy that has actually come back to this forum with a LTFT value so it appears that you have a good scanner and can read live data streams..

So what were the conditions prevailing when the Limp Home was initiated as recored on the ECU flash memory? Out of interest what is the normal idle STFT?

After changing so many parts have the same DTC's reappeared after they were cancelled?
When you start the engine or only after the car has gone into limp home?

I suspect that there is something missing / not quite right in the data you have provided.

Speedo drops to 0mph?


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Old 05-20-2008, 09:31 AM
Join Date: May 2008
Posts: 2
Default RE: Engine check light DTC P0170 and P0173 fuel trim system malfunction

I have had the exact same problems with my 1999 c230 Kompressor. I had been getting the p0170 codes which then deteriorated to a perfomance issue of jerking, loss of acceleration, and finally stalling. I have the official service star CD from MBZ, it ran me 175 bucks but I think it was worth it. So I followed the instructions on the cd and replaced the MAF first (ebay $65),I then went andreplaced the oil separator and breather line from the oil separator to the valve cover, then Ireplaced therubber vacuum hose from thebreather hose tothe intake (and use a pipe cleaner to clean out those two vacuum ports on the intake). The residual oilmessed up my new MAF soIcleaned it and recleaned it. I was going about 200 miles between p0170 codes, I knew there would residual oil because I didn't disassemble the intercooler, turbo etc. It's just to much ofa pain, it's easier to keepcleaning the MAF, eh whatever.

The stalling issue is NOT related to theMAF!!Stalling,sputtering and jerking, loss of power, loss of accelleration WITHOUT throwing off a code and turning on the check engine light CEL is an ignition coil issue. On my car, the 111 engine, I have two coils, so for $65 bucks each ($130 total)from the majority of myproblems are solved.

Now the most recent problem isIgot a new code, P0100 a general MAF failure. Once againI may have to get a new MAF off ebay.Iknow I shouldpull thewhole intake apart and clean outever last bitof oil(then install a catch can on the oil separator line to the airbox) but that is so much work! I dread the thought. And for all those that don't know it, this is the most common problem of the 97-99 C230's. I have been to every forum on the net and I see it all over the place, you are not alone.
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Old 05-20-2008, 11:31 AM
Join Date: May 2007
Posts: 1,057
Default RE: Engine check light DTC P0170 and P0173 fuel trim system malfunction

Here in lies your problem
a real bosch mass air sensor is about 170 dollars,if you buy off ebay it is a cheap chinese clone that some supplier buys for 17 bucks by the container load and sells them to bargain hunters.Get the real deal and your p0170 and p0173 fuel trim code will be resolved.Never buy critical engine parts off or ebay.
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Old 05-20-2008, 11:21 PM
Senior Member
Join Date: Dec 2004
Posts: 2,409
Default RE: Engine check light DTC P0170 and P0173 fuel trim system malfunction

Just for a bit of a tease I hope you don't have a P0170 AND a P0173 on your SLK unless you have a V6 in it.
P0173 is Fuel Trim on Bank 2!
M111/m112 etc engines seem to be VERY SENSITIVE to MAF.
As a consequence I endorse buying the real deal sensor not some copy.

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Old 05-30-2008, 10:10 PM
Join Date: May 2008
Posts: 2
Default RE: Engine check light DTC P0170 and P0173 fuel trim system malfunction

ohlord is correct! Ebay MAF-ED me, I too was burned, that damn MAF is a bad bad MAF. I just went to and got a real one for 175 and change.

So how do you know you have a bad MAF? Here is the test, and it's a good one; just unplug your MAF, start your carand drive your car. If the car is running better WITHOUT the MAF then you have a MAF problem.It's a more definite test than the code reader, (Yeah,I use the code reader,Ijust don't trust it).

I will never buy a MAF off of ebay again! GermanStar and Autohaus sell the real deal and that is what I am going to stick with from now on. Sometimes you have to learn these things the hard way, ouch!
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Old 05-30-2008, 10:10 PM

97, bank, c230, code, codes, diagnostic, dtc, fuel, malfunction, mercedes, p0170, p0173, panel, trim, trouble

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