I have a problem of no speed from the speed sensor while cranking with no start

[Peedee61]

I have a spare crankshaft sensors I have tried, I checked the wiring from the plug back to the ecu and have continuity, I bought a new crack shaft sensor (g2 and still no start or engine speed while cranking, I now have a bad feeling that something has fried the ecu, any fresh ideas for me please.

[DV52]

@Peedee61: Of course anything is possible - so there is a finite probability that the internal circuits in the ECU have gone pear-shape. However, I suspect that the probability of the problem here being a component failure external to the ECU is far greater!!

I'm not sure which particular engine is installed in this car - but it's quite likely that G28 is a Hall-effect sensor (i.e. this engine does NOT use an inductive type speed sensor). My assumption can be confirmed if the sensor has a 3 x pin connector.

The general set-up for a Hall effect sensor is like this (I thieved the picture from the web) :



As you can see- these senors use an external power supply (labelled "Vcc" in my diagram). In your engine, this power-supply is 5Volts - which is generated by the ECU. There is also a ground pin for the 5Volts which is different to car earth and the remaining pin is the pulsed voltage that is the speed signal to the ECU.

I'm not sure about this particular G28 sensor - but normally on these 3 x pin connectors:

• 5 Volts = pin #1
• Signal = pin #2
• Earth = pin #3

The best way to check the operation of this sensor is with an oscilloscope because it will show how the voltages change with time - but it's unlikely that you will have access to a scope. There are a number of You-tube videos that describe how to use a multi-meter to check the operation of Hall-effect sensors

So - the way to check the wiring for this sensor is to grab a multi-meter and first measure if the +5Volt power supply is present at the 3 x pin sensor connector. It's unlikely that the +5Volt supply from the ECU is faulty because this same power supply is used for other Hall-effect sensors on the engine -but it may be absent at the connector on this particular sensor.

The other possible reason for this fault could be the condition of the air-gap between the sensor and the toothed wheel. Shine a torch onto the gap and check that it's clean and free from detritus.


Don

[Peedee61]

Hi DV 52 yes it is the 3 pin sensor, it has the 5 volt supply from the ecu it has the negative feed from the pin at the sensor, no unfortunately I do not have access to an oscilloscope,
would passing a metal object in front of the sensor create a 5 volt return to ecu ( which is what I believe it should be) as I stated I have traced the wiring from the ecu to the sensor and have continuity on all 3 wires
the engine is the cabby common rail diesel of 103 kw I replaced this motor in June and still have not managed to get it to run, when attempting to start I get 0 rpm but get other items that show reasonably correctly to specs, such as high fuel pressure starts at 8 bar but quickly jumps to around 40 to 45 bar I get injector pulse length and quantity, I can smell the exhaust is so close to the start after a prolonged crank .
i have had the top of this motor off to double check there was no physical mechanical issue, and I have replaced the rear main seal as it was 1 leaking and 2 the timing ring had been set aligned with the sensor not at the correct spot while at tdc, which I did by buying the correct tool to install and align it.
thank you for your input.
one question if I go looking at ecu’s would buying the complete set of immobiliser, key, and ecu be better and just work asplug and play or just get the ecu and have it coded, I do not trust our local dealer he had the car for 3 weeks claimed it was the g28 crankshaft sensor but then also stated the engine that I had gotten from the wrecker was sold in Australia but they had no access to a wiring diagram for it, I’m currently using one that has been converted from Russian and all the wiring and colours have matched so far, got the feeling from them it’s only an older car who cares they should get a new one

[Peedee61]

Doubled up

[MIG]

Is the engine code the same as what the ECU is from? It's common for the tone rings to change patterns between engines.


Also, regarding the immobiliser stuff, most VWs need ECU, keys and Cluster; you are better off matching the ECU to the existing VIN

[Peedee61]

Hi yes the tone rings caused me all sorts of issues as mine has 2 raised teeth at 180 degrees apart the first one I got of eBay had holes in it and the seller insited that it was correct after having to send pictures to him showing the difference and stating I was not going to use it, my local parts supplier also was unsure so, I scoured the local sources and found repo had the correct one via picture but was miles away from me, so ordered it to my local store and if not correct would be able to leave it, when it arrived it was the correct tone ring.
The engine code is exactly the same the car it came out of was only a month younger than mine. Both CBAB prefix engines
Thank you that is one of my question's answered regarding the ecu

[MIG]

Are any errors stored on the ECU? A no signal or correlation error would help point us in the right direction.
Otherwise, without a scope, it's going to be hard to be certain what the issue is. (Pico scope is $180, multimeter scopes can be even cheaper)


Something like this.
000022 - Bank 1: CMP Sensor (G40) / Engine Speed Sensor (G2
P0016 - 000 - Incorrect Correlation

[DV52]

would passing a metal object in front of the sensor create a 5 volt return to ecu

Yes (albeit I don't quite understand the bit about "a 5 volt return path")!
Do the steps below as the first of a 2 x part test:

1. Remove the Hall-effect sensor from the car and plug-in the connector so that the sensor is energized properly
2. Make sure that the sensor end is NOT near any metal parts - Switch-ON ignition.
3. Switch the multi-meter to the 20V DC scale and connect the multi-meter negative lead to battery earth
4. Connect the multi-meter +ve lead to the +5V pin on the sensor - is the reading +5V?
5. Connect the multi-meter +ve lead to the earth pin on the sensor - is the reading near 0V?
6. Connect the multi-meter +ve lead lead to the signal pin on the sensor
7. Move a large spanner near the sensor - the actual reading on the multi-meter will vary depending on lots of things - but if the sensor is good, you should see a change in the multi-meter voltage reading from +5V to near 0V.

So, the steps above will test if the sensor is OK. However, the procedure above does NOT say anything about the ability of the sensor to provide a stream of kosher square-wave pulses to the ECU when bolted into the engine housing. To test the condition of the sensor-circuit (as distinct from the sensor itself) - you need to check if the "reluctance wheel" (i.e. the "tone rings" in @MIG response) and the air-gap is OK.

For the "sensor circuit" test - do this:

1. Replace the sensor back in its position on the engine
2. Disable the engine so that it won't start (maybe disable the fuel system)
3. With the multi-meter switched to 20V DC scale -connect the multi-meter +ve lead to the signal pin on the sensor and the -ve lead to battery earth
4. with ignition -ON, slowly rotate the the crankshaft using a socket wrench with a long handle. If the reluctance wheel/air-gap is OK - you should see the voltage switch from +5V to near 0V as the crankshaft rotates. Note: it's important in this test that the lower voltage is close-to 0V - I've seen some sensor-circuit signals that look OK at the +5V end - but they have a high reading at the low-end of the square-wave. The ECU uses a "hysteresis-circuit" to detect the rising/trailing edge of the square-wave pulses - proper detection of the high/low points defines the way that the ECU understands the stream of pulses in the waveform. This means that the sensor signal needs to have an almost FULL 5V change to trigger the upper/lower threshold levels in the hysteresis design (apology for launching into techno-geek babble!! )

I like @MIG suggestion about buying a cheap scope. However, it's one thing to have access to such a device - but it's an entirely different matter to understand how to use it in a way that makes sense. Please don't take offense - I've absolutely no doubt that you could learn the operation of an oscilloscope (it ain't a difficult device to drive). The thing about an oscilloscope is getting the square wave pulses to stabilize on the screen - this requires a user to select the proper time base for the incoming signal plus the proper trigger mode. Again, not difficult - but it DOES require a basic understanding of time based signals and how to capture the pulses.

one question if I go looking at ecu’s would buying the complete set of immobiliser, key, and ecu be better and just work asplug and play or just get the ecu and have it coded, I do not trust our local dealer he had the car for 3 weeks claimed it was the g28 crankshaft sensor but then also stated the engine that I had gotten from the wrecker was sold in Australia but they had no access to a wiring diagram for it, I’m currently using one that has been converted from Russian and all the wiring and colours have matched so far, got the feeling from them it’s only an older car who cares they should get a new one

What @MIG said!!

[DV52]

@Peedee61:
Here's the pin-out and wiring diagram for G28 on the Tiggy ECU for a CBAB engine:


If you aren't familiar with VW nomenclature - T60 /52 means pin #52 on the ECU connector that has a total of 60 x pins.

Don

[Peedee61]

Hi DV52 I have traced the wiring from the sensor pin 1 in the connector has 5 volt power which is in the engine bay wiring harness, pin 3 has a continuous earth when measured with a multi meter and pin 2 the sensor wire has continuity to plug 60 at pin 54 ,the sensor wire goes to the 60 pin plug at the ecu and joins pin 52.

I did download the 19 page tutorial from ross tech on how to read the wiring diagrams and studied that for a couple of days to get my head around what seemed to be some strange language but eventually it made sense if thinking of it as an engineering diagram

I do have a code being coolant pump 2 short to ground, I have disconnected this plug and traced its wiring from plug T3bc pin one continuity to earth, pin 2 goes to fuse holder B fuse number 23 12 volt, pin 3 goes to the ecu plug with 94 pins and connects at pin 68 and has continuity.

I did have a code for p0016 CMP sensor (G4) / engine speed sensor (G28 ) incorrect correlation, which I re adjusted the cam timing with the tools and had the code cleared and has not returned.
Now I have a code for Engine speed sensor (g28 p0332 no signal since putting in the new sensor, (which by the way is a pain as you have to remove the oil filter/ cooler housing from the front of the engine to access the Allen key bolt, and there is no way that I can see to alter the sensor to tone ring gap as the sensor bolts to the engine block inside a gap in the bell housing