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  • G40 Cam Position Sensor (CPS) info
    Posted by: UrS4boy (137) on 2009-12-12 20:48:36

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    G40 Cam Sensor
    Our 20vt AAN (and ABY and ADU) engines need good signals from three sensors to start and run properly. These sensors are the G4 Crank Position Sensor, the G28 Engine Speed Sensor and the G40 Cam Position Sensor. The G28 engine speed sensor is the trigger for firing the fuel pump relay which also opens power up to a number of devices. The G4 crank sensor and the G40 Cam Position Sensor are needed by the ECU to determine exactly where the engine TDC is. This is because on any four stroke engine, the crankshaft turns twice as fast as the camshaft - so with G4 alone on the cranks at 62 degrees btdc it's impossible to know if the engine is on the compression or exhaust stroke. The purpose of G40 is to identify the camshaft position and therefore determine the phase of the engine so that ecu has all the info it needs to start initiating coil and injector activation. (Reference: Paul N., S2Central.net). After the engine is running, the ECU can run on G4 alone if the G40 fails - however, the ECU will retard the timing signifiantly if the G40 fails while running. While the fuel pump relay is still energized with a failed G40, the ECU will not fire the ignition on restart because it needs both the G40 and the G4 crank sensor signals to do so. (Or at least that is supposed to be how it works - see below).

    Here is a crude sketch I did to show the relationship between the camshaft and the crankshaft, showing how the camshaft rotates at half the speed of the crankshaft, implying the need for signals from *both* the G40 Camshaft position sensor and the G4 Crankshaft position sensor:

    Here are some G4,G28 and G40 wave forms for you to ponder:

    The G40 Cam Position Sensor (CPS) is a Hall Effects Sensor used by our AAN engine's ECU (Engine Control Unit, i.e. the Motronic Computer) to figure out where the pistons are and where TDC for Cylinder 1 is, so it can trigger the correct spark and fueling sequence. Once the engine is running, the ECU will use the G4 crank sensor position sensor to keep track of things. If the G40 cam sensor fails, a "2113" blink code will be thrown (into memory) and check engine light will come on. If the G40 CPS fails while running, you can keep driving but as soon as you turn the engine off, you are done. The engine will NOT re-fire until you fix the cam sensor. You might get lucky once or twice by cooling the cam sender down (try pouring water down the back of the cam belt cover) Location photo and diagrams in the URL links below. Link to info on pulling blink codes HERE.

    One thing to watch for is an intermittent G40 Short to Ground (VAGcom code 00515). In this case, the G40 is failing and that short to ground will stop the engine from running, despite what we *think* the ECU should do with the G4 Crank Position Sender signal to keep the engine running. Sometimes reality is stronger than theory. Here is a link to a documented case that the 00515 intermittent G40 short to ground code will stop a running engine. (Click)

    The G40 typically lives behind the exhaust cam sprocket but on the very early AAN engines, it was located in a vestigial distributor ("tuna can" underneath the intake manifold, driven off the intake camshaft, much the same as a 7A or 3B engine):

    Here is what the early AAN "Tuna Can" Hall sender case looks like in the engine bay:

    Here is the Early AAN Hall Sender in a can out of the engine:

    Here is a fuzzy photo of the tuna can dizzy shutter wheel and camshaft position sensor showing the two alignment marks that need to be together when the camshaft and crankshaft timing marks are at top dead center (TDC) (might be tricky because of the dizzy drive teeth - but you have to get it right - there is some adjustment on the dizzy though so hang in there):

    Here is the end of the AAN intake cam (in the right hand photo, the left hand photo is a 3B) showing the gear driving this Cam Sensor in a can:

    Photo: Thanks to Jari Aalto

    Here is what the later AAN and ABY and ADU Hall sender looks like:

    Hidden behind the cam shaft pulley and the integral cam shaft position sender shutter wheel:

    Here is a photo showing the back side of the AAN (and ABY) exhaust cam sprocket, showing the shutter wheel that is precisely spot welded to the cam sprocket and the opening ("shutter") in the shutter wheel that triggers the G40 to send its cam position signal to the ECU. Note how the red line from the cam timing mark through the center of the wheel/sprocket lines up with one of the edges of the shutter opening.

    Thanks to Scott N. for providing the base photo.

    Exposed with the cam pulley and integral shutter wheel removed:

    There was also a period when the factory modified 3B or early AAN heads to mount the cam sensor at the front of the engine. This transition period is documented HERE

    This is what VAG says about the G40:

    The connection to the ECU is via Pins 12 (power) and Pin 8 (signal)

    Here are some photos of the G40 Cam Position Sender and its wiring:

    If you are clever, you can set up an LED to show you that the CPS is working properly by connecting an LED between Pins 1/3 and 2/3, using instructions written by Marc S. at EFI Express

    Photo courtesy of Marc S. at EFI Express.

    If your cam sensor fails, you need to replace it with a new 034905161, complete with bracket, as shown here (item 10):

    [NOTE: In the above, the three pin female connector housing to connect the coils to the POSs (which have integral male pins on both ends) is Audi 433906233 (AMP 929552) (item 23 above). The three pin MALE connector housings for the primary power from the two white harness connectors to the coils don't show a Audi PN on the white male version (no jokes please) other than "DM4 Austria" and "510011-1500". (These can be scrounged from 3 pin VW Golf III O2 sensors in a pinch). However, as it turns out, the 3 pin male for the female 433906233 is 443906247 (Item 24 below) which should work (other than the colour) (Note the "21" and "22" pairing in the second diagram). (I have new white ones in my hand but no invoice but I bought them from a VAG parts dealer (about 5 years ago))]

    ** OR **

    Purchase just the Hall Sender (HME301)

    from EFI Express

    Installation of either the new OE part, or the BB AutoMacao sender (on your OE bracket (be careful prying the bracket away from the head, they will break) has been excellently documented by Nate P. (ImQuattro) HERE

    The VIN breakpoint for the "tuna can" hall sender occurs in about mid-February 1992, as discussed HERE If you have a "tuna can" Hall sender and the sender fails. You can still replace it because the OE sender was a Siemens HKZ101 and the BB AutoMacao HME301 works just like in the later AAN (and ABY and ADU) replacements. Here is a link to the 7A, 3B and Early AAN Hall sender replacement DIY.

    From time to time, with age, the Cam Position Sensor connectors get brittle and break, either at the harness end or the cam sensor itself as shown here:

    Photo courtesy of Dennis1987 on the S2 forum.

    At least the brittleness allows us to peak inside the broken G40 connector above (normally the pins are not removable) to see that Pin 1 = red, Pin 2 = green and Pin 3= black (that observation courtesy of Nate P. (ImQuattro))

    The harness connector with the female pins is PN 443906233, as shown here, as item 15 below and item 21 below that:

    The cam position sensor connector has the male pins. The OE cam sensor pins are "potted" in the connector and cannot be removed. If the connector crumbles, it can be replaced by the Item 22 443906247 male pin connector above, along with separate pins and sealing grommets. Alternatively, VW Golf/Jetta III three pin O2 sensor connectors can be used in this application (some splicing might be required).

    One final note: When you are playing with your cams or cam sprocket, use a proper tool to hold the cam sprocket when you remove the bolt in the center of the sprocket. DO NOT jamb a big screwdriver through one of the big holes to hold the sprocket. This can damage (bend) the shutter wheel, causing strange running and intermittent engine stopping issues until the cam sprocket was pulled to reveal this bend:

    Photo courtesy of Mathias on the S2Forum.

    Thanks to those who posted the diagrams.

    This *will* be on the exam.
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