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- - P0170 code (https://mercedesforum.com/forum/mercedes-c-class-10/p0170-code-805/)

I just purchased a used c230 1997, the check engine is on, Checked it at an independent shop, the print out that he handed to me stated p0170 is the OBD II code. At AutoZone I saw it reading p0170 and p0136. II am not sure if they are two different problem or they are related. Any idea will help. The tranny shift harder than normal.<edited><editID>ahasanat</editID><editDate>38007.888125</editDate></edited>

Your PO 170 code has to do with "Fuel Trim Malfunction". Some of the causes for this code are as follows:

1. Intake air leak

2. Injectors

3. Fuel Pressure Regulator

What's happening is your engine computer is not able to compensate for an extremely rich condition or lean. Basically it's maxed the limits on fuel trim for whatever problem you have. I would start with an intake leak (vacuum leak) somewhere on your engine because that will also cause the erratic shifting your talking about. Let us know what you find!!

As I re-read your message I realized you have a code 136 as well, this is related to a faulty 02 sensor of which will cause a code 170. Forget everything I wrote earlier, your 02 sensor is bad and needs replacing.

Thanks Dale
After reviewing some topic on this forum, I noticed many refere to this problem as trim malfunction on bank 1. An injector leak or air vacuum leak or pressure regulator can cause this code. Most of time changing the MAF solves this problem. How can the dealer or I tell without guessing by replacing the MAF will fix this problem? Can I disconnect the MAF cable and try to run the car for couple min to look for changes, would this harm other devices on the car? How I can check for air vacuum leak, injector leak or pressure regulator problem. What it will take to dealer to diagnose this problem fairly.

<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p>1st O2 Sensor was showing jumping btw .1v to .9v onthe scanner on real time.</o:p>
<o:p>2nd O2 senser was at 1.3v</o:p>
Also I am seeing that Techron is recommended to clean inside the engine, can I use it on this car (1997 c230).

<edited><editID>ahasanat</editID><editDate>38007.8848958333</editDate></edited>

The car won't run with the MAF disconnected so don't try it. If you've recently changed the O2 sensor than you shouldn't have a PO 136. Check the connection going to the sensor, it may not be seated enough or loose. As far as a vacuum leak goes I would look at the vacuum line going to your fuel pressure regulator and your modulator valve on the transmission.

When you check the O2 sensor, make sure nothing foreign is on it around the threads. I've heard so many times of "technicians" putting a sealant, anti-seize, or some other fumy gunk on them. The sensor will "read" the fumes and go beserk.They should be super cleanwith nothing on or near them that gives off fumes. They are also very easy to damage ifdropped or banged around during installation.

Thanks Dale

Did you experience any of the trans-shifting problems that I stated above?
Whatisa good reading range for the MAF for this car, whatis abad reading range for the MAF for this car?


while the car was running:
I saw the MAF .69lb/min I don’t know if this means any thing...Is the range in Volt or Lb/min

I saw the O2 ranging btw .1v and .9v. , I think this is good .

I can tell you the transmission in my wifes C230 shifts really hard into second all the time, hot or cold so I wouldn't be too concerned about the tranny just yet. First thing is to get rid of that PO 136. If your fuel trim is getting confused I can see how it would effect everything from shift quality to gas mileage. 

The MAF readings your seeing don't really mean a whole lot because it's only reporting air flow and temp. to the ECU. If it was bad you would get another code so I would stay away from it for the time being and focus on what the computer is telling you and that's the 136. I've been in your position before when it comes to troubleshooting problems, after replacing a lot of good parts you find out the computer was right all along so dig deep into the O2 sensor code and get back with us.......When you've fixed that I believe the other code will go away and you'll be back cruising on main street again!!!

Your range of .1 to .9 is fine although I would like to see it up around 1.3v. It might be time to bite the bullet and install a new O2 sensor before we go any deeper with this problem, and that's only if your sure you don't have a vacuum leak to the fuel pressure regulator or anywhere else on the engine. A normal vacuum reading at idle is a steady 17 to 18 inches.

how to check foranormal vacum reading and which part control the vacum on this car. thnaks<edited><editID>ahasanat</editID><editDate>38007.8857060185</editDate></edited>

you can pull pretty much any vacuum line off you want that will fit onto the gauge because all your looking for is a steady reading. And yes a vacuum leak will cause the tranny to shift harder than normal because the modulator valve on the transmission relies on vacuum to determine shifts and band pressure.