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  • G70 Mass Air Flow (MAF) sensor info
    Posted by: UrS4boy (137) on 2009-11-21 20:16:53

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    Our cars use a hot wire anemometer mass air flow sensor to measure the air flow going to the engine. This info is used by the ECU to decide how much fuel to inject by controlling the fuel injector duty pressure (as related to the boost pressure).

    Here is how the MAF fits into the overall engine control picture:



    Here is what Audi says about the MAF:



    Here is an RS2 MAF on an UrS4 airbox, showing what you would have to do in order to remove it for cleaning and/or inspection/replacement:



    Here is what the small inner sampling tube and hot-wire look like (note the dirt in the tube):

    Photo courtesy of deephouse (Brian C).(Taken with "Macro" on)

    As far as I can tell, the mass air flow sensor (MAF) for the ABY S2 is the same as that for the RR Urq, the 3B S2 and 200 20vt and the UrS4 and UrS6 (all same PN 034133471K)(Bosch 0 280 213 007). The RS2 MAF is similar but different (wider opening screens) (PN 034133471N). (See photo below: 471K on he left, RS2 471N on the right). In both cases, when the engine is shut off, the ECU sends a current to the MAF hotwire that is enough to burn off the crud that has accumulated. (NOTE: PN update the 471N RS2 MAF is the same as a 944 turbo MAF PN 951.606.125.02 (Bosch 0 280 213 017)). Scarman (Tom G) found some interesting info about Bosch remanned MAF PNs HERE


    Image courtesy of Jimmy Pribble

    Airflow of the RS2 MAF is superior to the 471K, as pointed out in a post by Manx:

    Click here to see what Manx found

    Removing the inlet screen on the 471K will improve air flow but could lead to turbulence across the hot wire (and therefore bad signals). Not too much is said about the rear 471K screen.

    The electrical signals from the 471K and the RS2 MAFs are similar. Close enough that, in the last few years, tuners have been tuning using the 471K, even with RS2 and above turbos. BUT remember, the airflow is still less with the 471K with the screens intact.

    Here is what Cody Payne found out about the 471K and RS2 471N output voltages:



    "prj" (dmitri) on the S2Forum had a look at the above graph and commented:

    "I can confirm from factory data now, that they are completely identical electrically.The difference on that graph is likely because not two brand new units were compared and because they are within a 3% error margin anyway.That graph to me looks like they used an AAN maf with some miles on and a brand new ADU MAF."
    Reference Thread, post No. 9

    The MAF connector sometimes develops some corrosion and may need to be cleaned and Stabilant 22 added (to keep the corrosion at bay). If there is more trouble, you might want to replace the connector.

    As with all Audi electrical devices, the power is brought to the device in a female flat pin connector that mates up (no pun intended) with the male pins that stick out of the device that is to be powered, in this case, the MAF. In the case of the MAF, it's a flat six pin female connector or "terminal housing" in Audispeak. Here is a look at a dirty connector on the MAF:

    Photo courtesy of deephouse (Brian C)

    The PN for this six pin connector was originally 022 906 233 A. However, at some point, it was dropped and replaced by 025 906 238 B. The female pins for this connector typically come two on a yellow covered pig tail wire. The PN for these female connectors is 000 979 133 or 133A for the 1 mm wide pins or 225 or 225 A for the 2.5 mm wide pins. The "A" is for the gold-plated version (slightly more costly but likely the ones you want if corrosion is a problem).

    NOTE: Another MAF problem is sometimes the male pins of the MAF miss the "target" on the female pins and end up pushing the female pins backwards, out of the harness MAF connector, as shown here for the similar throttle/idle switch connector:



    This is what a good MAF harness connector looks like:




    If that is the case, all sorts of wierd missing happens (poor connection) and maybe even a 4411 code (i.e. injector No. 1 fault). The solution is to clean the connection (male and female pins) and then after reconnecting, pushing the female pins individiually, from the back of the connector towards the MAF to make sure they are properly mated with the male pins.

    For the MAF harness connector the female pins are only in positions 1 through 5; No. 6 the one at the left end of the connector is empty. For the AAN MAF harness connector, the five pins are as follows:

    Pin 1 = Brown with red stripe, goes to a ground (16) (on the cylinder head (cam) cover)
    Pin 2 = Red with black stripe, goes to pin T26/55 in the ECU
    Pin 3 = Green with white stripe, goes to pin T7/55 in the ECU
    Pin 4 = Green with purple (violet) stripe, goes to pin T25/55 in the ECU. This is the burn-off signal wire from the Holding Relay
    Pin 5 = Black with red stripe, connects to the fuel injector harness

    Here is a photo showing those five AAN wires:



    Testing the G70 MAF is found in the Bentley in section J24, Volume One, pgs. J24-77 to J24-85. The following is a short-form summary of this info and is not complete:

    1. Testing for ground: Disconnect the harness connector from the MAF. Set your DMM to 20 ohms and look for continuity between Pin 1 (Pin 6 is the empty position) and ground on the engine or chassis. Not continuity = you have a ground issue involving that Brown/red wire. Start tracing back, looking for a broken wire. Won't be fun.

    2. Testing for connection to the injector circuit: Turn the DMM to 20 VDC. Connect to Pin 5 and ground. Turn on the ignition. You should get some positive DC volts.

    3. Checking MAF function: With harness connector removed, switch DMM to 200 ohms. Connect DMM probes to terminals 1 and 2 on the MAF (1 is on the right, 6 is on the left). Record the resistance. Disconnect leads and "Short" the circuit (press probe ends together). Display value must equal value recorded previously.

    If the difference is greater than 0.1 Ohm, replace MAF.

    Re-connect the MAF sensor harness connector. Peel back the rubber boot on the connector to expose the terminals. Switch the DMM to 20 VDC. Connect the DMM to the back side of Terminals 1 and 3. Turn the ignition switch to "ON" (run) but don't start the engine. Should be 1.2 to 1.5 Volts. Start the engine and let idle. Voltage reading should now be 2.5 volts. Increase the engine speed briefly (manually move the throttle position to more open). Voltage should increase to 3.0 to 5.0 volts (depending on engine speed). All the of the specified voltages must be obtained. If NO = replace MAF.

    Here is a link to a G70 MAF testing worksheet that you can print off and take out to your UrS when testing the MAF.

    There is more re: Holding relay/burn-off wire but that shouldn't directly affect running and idling.

    For the ABY and ADU, the connector is the same general configuration but the wiring is different:

    The wiring listing for the ADU MAF connector is:

    Position 1 = Brown/yellow to (138) ground (probably the intake manifold?)
    Position 2 = Black/green from Pin T55/26 in the ADU ECU (looks like this one might be a white/green wire for an ABY)
    Position 3 = Black/white from Pin T55/7 in the ADU ECU
    Position 4 = Blue/violet from Pin T55/25 (holding relay) in the ADU ECU
    Position 5 = Blue/black 12V power wire connected to the injector wire power circuit which is connected to Pin T55/37 in the ADU ECU (actually from the Holding Relay in the ECU)

    Here is a photo of an ABY MAF connector.


    Photo courtesy of Bilko0795 on the S2Forum.

    Here is a schematic showing the ADU G70 MAF wiring schematic:



    When you turn the engine off, the Holding Relay sends power to the MAF via Pin 37/55 to Pin 4/5 of the MAF connector for 5 seconds to burn-off any contaminants on the MAF hot wire. *IF* the holding relay fails closed, it will power Pins 4 and 5 <b>*FOREVER*</a> (or until the battery goes flat). In doing so, it will heat the metal portion of the MAF up until it is skin-burning hot, as discussed in this post.



    More detailed G70 MAF info by Paul N. of the S2 forum HERE

    Recently on the S2Forum, "Colesy" posted up an issue: idle was dropping off to a stall and there was hesitating under acceleration. We gave him the usual pointers, i.e. MAF, boost leak, etc. and encouraged him to check his MAF.

    He pulled the codes and said that he would set about cleaning the MAF and boost leak testing. In the meantime, he posted the codes:

    00561 - Mixture Adaptation
    13-10 - Adaptation Limit (Mul) Not Reached - Intermittent
    00553 - G70 signal too low
    07-00 - Please Register/Activate
    00537 - Lambda -regulating limit exceeded
    11-00 - Please Register/Activate

    He said that "When I started it up it stalled. But on second start the it idled perfectly for 10 mins or so until it started to get warm and the idle started dropping off and threatning to stall again...Hopefully it will be an easy MAF clean but having had MAF problems before I'm thinking it's something else".

    Well, he finally pulled the MAF to clean it and discovered the issue: The hotwire in the MAF sampling tube had broken, where the "X" is in the photo. Fortunately, he had a good spare MAF to install. He said "Quite annoying as it was a fairly new MAF! Had a spare in the stores though which I have fitted and it is back on song. Might have to pencil me in for an RS4 MAF conversion Dmitri!" (Dmitri (prj) in Estonia has been working on an RS4 MAF alternative for the UrS).

    I think Hap has had MAF wire issues in the past and has since abandoned the use of the MAF, as have some running VEMS.



    This will be on the exam.

    Thanks to those who posted the diagrams and photos used in this post.
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