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Advice on Fault Code's

Discussion in 'A3/S3 Forum (8L Chassis)' started by LiveWire, Dec 19, 2010.

  1. LiveWire
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    LiveWire S3X

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    [Dec 19, 2010]
    Hi Guys, Looking for some advice for what could be casuing these codes?

    17705 drop between turbo and throttle valve p1297 intermittent.
    17545 fuel trim bank 1 system to rich p1137.

    First code I guess is being caused by a boost leak?
    I pretty sure my cat is fu**ed so could the second code be something to do with that?

    Any advice appreaciated :thumbsup:
    #1
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  3. jc_1989
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    jc_1989 Member

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    [Dec 19, 2010]
    i know that air mass sensors are prone to going wrong on the 1.8T engines, that can cause a rich or lean fuel mixture if its not calculating the correct amount of air passing through it.... just a thought??
    #2
  4. s3dave
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    s3dave TFSI Hybrid Supporter

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    [Dec 19, 2010]
    17545/P1137/004407 - Fuel Trim: Bank 1 (Add): System too Rich

    Possible Symptoms

    • Malfunction Indicator Light (MIL) active
    Possible Causes
    • Mass Air Flow (MAF) Sensor faulty
    • Fuel Pressure Regulator faulty
    • Fuel Injector(s) faulty
    • Oxygen Sensor Control faulty
      • Oxygen Sensor(s) faulty
    • Evaporative Emission (EVAP) System faulty
    Possible Solutions
    • Check Mass Air Flow (MAF) Sensor
    • Check Fuel Pressure Regulator
    • Check Fuel Injector(s)
    • Check Oxygen Sensor Control
      • Check Oxygen Sensor(s)
    • Check Evaporative Emission (EVAP) System
    Understanding Fuel Trim

    Some of the most common Fault Codes (DTC's) pertain to fuel trim (rich mixture, lean mixture, etc.) Here is an explanation of fuel trim and what it does for us. The ECU controls Air/Fuel mixture in order to maintain power, efficiency, and emissions. A/F is expressed as either a ratio (14.7:1 for example) or as a Lambda value. With iso-octane ("ideal" gasoline), Lambda of 1.0 is equal to 14.7:1 A/F. This is known as "Stoichiometric", a condition where there is a perfect balance between oxygen molecules and the various hydrogen and carbon based molecules in petroleum. With the oxygenated gasoline that most of us use, actual A/F ratio of 15:1 is closer to stoichiometric.If Lambda is greater than 1.0, then there is a surplus of air and the engine is running lean. If Lambda is less than 1.0, then there is a surplus of fuel and the engine is running rich. It should be noted that the ratios are mass-based, not volume-based.

    So, why don't we always run at 1.0 all the time? Well, we do MOST of the time. At cruise and idle, mixture is held tightly to 1.0 to keep the catalytic convertor at optimal efficiency, so the emissions are minimized. However, when we need acceleration, the mixture gets richer. Why? Maximum power is made between 0.85 to 0.95 Lambda (12.5 to 14.0 A/F with iso-octane). So, under acceleration, mixtures get richer. Sometimes you want to get even richer under acceleration to keep detonation (pre-ignition of the mixture from excess cylinder temperatures) away. The 1.8T has a relatively high compression ratio for a turbocharged engine, which especially under lots of boost, is very succeptible to detonation).

    So, now that we know that the ECU wants to be able to control the A/F ratio. It has a prescribed set of values (maps) for a given RPM, Load, etc. So, the ECU tells the injectors to pulse for exactly XX.X milliseconds and that SHOULD get us the proper A/F ratio that we want. Well, if you tell an employee to go do something, you want to make sure they actually did it, right? The ECU has some snitches (the front O2 sensor and the MAF, for the most part) that will report back whether or not the desired mixture has been attained. The rear O2 sensor is used mostly to monitor the condition of the catalytic convertor, although in some applications it also contributes to trim information.

    Based on feedback from the snitches, the ECU learns to apply a correction factor to its commands to the fuel injectors. If you know that your employees take longer than the standard allotted time to do a specified job, you will need to adjust for that in your planning (injectors are in a union, so it is tough to fire them ). The learned values go between the maps in the ECU's Flash ROM (the "chip") and the signal to the fuel injectors. These learned compensations are known as "trim". So, when you see "trim", it means "compensation".

    "Add" means additive trim, which is addressing an imbalance at idle. When the ECU is using additive trim, it is telling the injectors to stay open a fixed amount longer or shorter. The malfunction (e.g. vacuum leak) becomes less significant as RPM increase. For additive adaptation values, the injection timing is changed by a fixed amount. This value is not dependent on the basic injection timing.

    "Mult" mean multiplicative trim, which is addressing an imbalance at all engine speeds. The malfunction (e.g. clogged injector) becomes more severe at increased RPM. For multiplicative adaptation values, there is a percentage change in injection timing. This change is dependent on the basic injection timing.

    You can check your current state of trim by using VAG-COM or equivalent to look in Group 032 (in many modern ECU's, consult your Factory Repair Manual for the specific group for your particular vehicle) in your engine measuring blocks. The first two fields will have percentages. The first field tells the fuel trim at idle (Additive). The second field tells the fuel trim at elevated engine speeds (Multiplicative). Negative values indicate that the engine is running too rich and oxygen sensor control is therefore making it more lean by reducing the amount of time that the injectors are open. Positive values indicate that the engine is running too lean and oxygen sensor control is therefore making it richer by increasing the amount of time that the injectors are open.

    It is totally normal for both the first and second fields to be something other than zero. In fact, zeros IN BOTH FIELDS indicates that either you just cleared codes (which will reset fuel trim values) or something isn't working properly. If values get too far away from zero, it will cause a DTC (fault code) and can set off the MIL (commonly referred to as the Check Engine Light, or CEL). Specifications for normal operation are usually somewhere near +/- 10%.

    In general, an out-of-spec value in the first field (Additive) indicates a vacuum leak since it is mostly present at idle, when vacuum is highest. An out-of-spec value in the second field (Multiplicative) indicates a fault at higher RPM, and may point to a faulty MAF.

    Here's a good sanity check for the status of your MAF. Do a full-throttle run all the way to redline in a single gear (second works fine). Group 002 usually shows air mass in g/s (in many modern ECU's, consult your Factory Repair Manual for the specific group for your particular vehicle). Your peak airflow should be roughly 0.80 times your horsepower if you are close to sea level. So, if you have a stock 150 hp 1.8T, expect around 120 g/s. If you see significantly less than that, you MAF may be on the way out. Also note that airflow will be markedly different at higher altitudes due to reduced ambient air pressure, especially with naturally aspirated engines that do not have forced induction to overcome that deficiency. This still works if you are chipped, but "race" programs may make more power through timing, rather than airflow. Therefore, take all readings with a grain of salt.


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  5. thorsy22
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    thorsy22 Member

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    [Dec 19, 2010]
    17536/P1128/004392 - Fuel Trim; Bank 1 (Mult): System too Lean

    Possible Symptoms


    • Malfunction Indicator Light (MIL) active
    Possible Causes


    • Mass Air Flow (MAF) Sensor faulty
    • Oxygen Sensor Control faulty
      • Oxygen Sensor(s) faulty
    • Fuel Injector(s) faulty
    Possible Solutions


    • Check Mass Air Flow (MAF) Sensor
    • Check Oxygen Sensor Control
      • Check Oxygen Sensor(s)
    • Check Fuel Injector(s)

    I'm getting this one, 99% sure its a knackered MAF as got a max reading of 112g's on a standard S3, want to do another log or 2 after I've replaced my knackered thermostat just to double check.
    #4
  6. Jay-a3
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    Jay-a3 Member

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    [Dec 20, 2010]
    i had these codes mate and they were because i didnt have a genuine bosh maf on the car.bought a new one and bobs your uncle!
    #5
  7. LiveWire
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    LiveWire S3X

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    [Dec 20, 2010]
    Thanks for the advice so far, I guess it could be the Maf then, I have access to vag-com so how can I check it is the Maf thats fuk**?

    I dont want to buy a new one if its not the problem.
    #6
  8. s3dave
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    s3dave TFSI Hybrid Supporter

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    [Dec 20, 2010]
    I bet you did not read what i posted...lol... log block 02 and see what g/s you are getting
    #7
  9. John_
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    John_ ---__---

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    [Jan 6, 2011]
    #8
  10. thorsy22
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    thorsy22 Member

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    [Jan 6, 2011]
    Replaced MAF and havent had any more DTC's come up, car is a bit more responsive too now.
    #9

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