P38A Stall speed monitoring gearbox fault

ar1g3 said:

A scope would allow me to rule out duff ECU, which I think is highly unlikely.

What would be nice is if I had a spare sensor to compare resistance with but at about 80€ excl postage I'm not gonna take a chance. So if anyone has STC4444 on the shelf and is able to take a measurement? Hehe

If that workshop manual can shine some light on how to get to the reluctor ring that would be helpful!

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Depending on your meter, with it set to AC, you may be able to detect pulses from the sensor. I'll have a look and see if the sensor is present on my spare gearbox.

ar1g3 said:

A scope would allow me to rule out duff ECU, which I think is highly unlikely.

What would be nice is if I had a spare sensor to compare resistance with but at about 80€ excl postage I'm not gonna take a chance. So if anyone has STC4444 on the shelf and is able to take a measurement? Hehe

If that workshop manual can shine some light on how to get to the reluctor ring that would be helpful!

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I have an HP24 sitting on my garage floor that I could take readings from. Not sure if its the same as the HP22.

If it is show me what and where you get your readings from. I will check mine.

J

marjon said:

I have an HP24 sitting on my garage floor that I could take readings from. Not sure if its the same as the HP22.

If it is show me what and where you get your readings from. I will check mine.

J

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@ar1g3 OK, so between pins E & D on the box, the sensor reads 307 ohms with the leads one way round and zero the other way round. RAVE shows the sensor as a semiconductor so the readings make sense.

marjon said:

I have an HP24 sitting on my garage floor that I could take readings from. Not sure if its the same as the HP22.

If it is show me what and where you get your readings from. I will check mine.

J

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HP22 & HP24 are, as far as I can determine, the same. I have given the readings above. You can find the pinouts in the connector ID in RAVE.

Datatek said:

HP22 & HP24 are, as far as I can determine, the same. I have given the readings above. You can find the pinouts in the connector ID in RAVE.

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I sort of thought they may be the same but had to ask.

I know I can find it in rave.
But it was a sort of show me where you get your measurements cos I am lazy and sometimes a pic shows more than you think

J

marjon said:

I have an HP24 sitting on my garage floor that I could take readings from. Not sure if its the same as the HP22.

If it is show me what and where you get your readings from. I will check mine.

J

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Seems like someone beat you to it so that saves you time and effort but thank you anyway for reference I was measuring on the ECU connector in the car itself, pins 42 and 14 for the post 99 V8.

Datatek said:

@ar1g3 OK, so between pins E & D on the box, the sensor reads 307 ohms with the leads one way round and zero the other way round. RAVE shows the sensor as a semiconductor so the readings make sense.

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Thanks! Only 2 ohms off the reading of mine, but I only checked one way. Will check both ways to confirm. In any case it's going to be an inductive sensor seen there's only 2 connections to the ECU (plus shield). So to pick up on your comment of measuring AC, that's a good tip!! I'll do that. If the sensor sees teeth passing it'll generate voltage so I don't need to see a scope image, if I get zero volts there I know that the reluctor is spinning on the shaft.

I will not be able to pop into the garage for the next 10 days but will do further measuring with above tips in mind after, and report back. Many thanks for the help already!

So I did a road test reading AC volts across the two sensor wires:
- at 50 kph --> 7mV
- at 70 kph --> 16mV
- at 90 kph --> 24mV

To me that just seems like noise, and not a signal.
Again checked resistance and comes back between 300-350 ohm which is a typical value for inductive speed sensors. I also check for shorting between the screen and the sensor but that's also not the issue. The screen is connected to ground I believe so a short to the screen would drain away the signal.

This was my setup (multimeter in wrong setting here, changed it before driving):


I guess next step is opening up the transmission..

ar1g3 said:

So I did a road test reading AC volts across the two sensor wires:
- at 50 kph --> 7mV
- at 70 kph --> 16mV
- at 90 kph --> 24mV

To me that just seems like noise, and not a signal.
Again checked resistance and comes back between 300-350 ohm which is a typical value for inductive speed sensors. I also check for shorting between the screen and the sensor but that's also not the issue. The screen is connected to ground I believe so a short to the screen would drain away the signal.

This was my setup (multimeter in wrong setting here, changed it before driving):
View attachment 310808

I guess next step is opening up the transmission..

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RAVE shows the sensor as a semiconductor, in other words and inductive sensor with a built in amplifier. If RAVE is correct (which is not always the case) you should be seeing a wave form on one wire and a fixed supply voltage on the other ground being provided by the metal casing. No supply voltage would mean no signal. I'll try and find it in the ZF manual for confirmation.

Datatek said:

RAVE shows the sensor as a semiconductor, in other words and inductive sensor with a built in amplifier. If RAVE is correct (which is not always the case) you should be seeing a wave form on one wire and a fixed supply voltage on the other ground being provided by the metal casing. No supply voltage would mean no signal. I'll try and find it in the ZF manual for confirmation.

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But would I then be able to measure 320 ohms across those two wires?

My voltage measurement seems to suggest something is happening because the measured AC voltage does increase with speed but is very low. So lets say this measurement is multiplied with 100 then we come into the range of voltage I would expect for an automotive sensor circuit.

There is a + and - marked on the sensor in RAVE which seems to suggest polarity is important.

EDIT: I do measure a voltage between ground and both sensor pins. This is with everything connected. I measure 2.3V between ground and each pin.

ar1g3 said:

But would I then be able to measure 320 ohms across those two wires?

My voltage measurement seems to suggest something is happening because the measured AC voltage does increase with speed but is very low. So lets say this measurement is multiplied with 100 then we come into the range of voltage I would expect for an automotive sensor circuit.

There is a + and - marked on the sensor in RAVE which seems to suggest polarity is important.

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As I said before, meter one way round, 307 ohms, the other way round open circuit which tells me it's not a simple inductor. The polarity marks also suggest it's not a simple inductor.
I didn't do any measurements from the case to the wires, perhaps I should have.

Datatek said:

As I said before, meter one way round, 307 ohms, the other way round open circuit which tells me it's not a simple inductor. The polarity marks also suggest it's not a simple inductor.
I didn't do any measurements from the case to the wires, perhaps I should have.

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Aha, but I get a resistance measurement regardless of polarity! I get the 320 ohms both ways.

ar1g3 said:

Aha, but I get a resistance measurement regardless of polarity! I get the 320 ohms both ways.

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That does not sound good. Unfortunately, apart from the resistance reading, the parts of the ZF service manual I have give no further details.

Datatek said:

That does not sound good. Unfortunately, apart from the resistance reading, the parts of the ZF service manual I have give no further details.

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So the manual does not tell that there is a difference in reading depending on polarity? You are sure that you did not get a reading in both ways?

I will disconnect the ECU tomorrow and measure on the connector there, if I still get the same result (both ways 320ohms) I think the conclusion is that the amp in the sensor has failed (which explains the mV readings above). To be honest if the sensor has broken then that is good news as far as I'm concerned. I'd rather replace that sensor than the ECU or start messing with the trigger wheel.

ar1g3 said:

So the manual does not tell that there is a difference in reading depending on polarity? You are sure that you did not get a reading in both ways?

I will disconnect the ECU tomorrow and measure on the connector there, if I still get the same result (both ways 320ohms) I think the conclusion is that the amp in the sensor has failed (which explains the mV readings above). To be honest if the sensor has broken then that is good news as far as I'm concerned. I'd rather replace that sensor than the ECU or start messing with the trigger wheel.

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I will do the measurement again tomorrow. Swapping the ECU is a heck of a lot easier than replacing the sensor, plenty available on the web and not expensive. Plug & play except for the 4.6.

Datatek said:

Plug & play except for the 4.6.

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?? Why?

J

Datatek said:

I will do the measurement again tomorrow. Swapping the ECU is a heck of a lot easier than replacing the sensor, plenty available on the web and not expensive. Plug & play except for the 4.6.

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Thanks already!

The reason I would prefer the sensor is that I need to open the gearbox anyway for a filter change, and with a used ECU you never know what you'll get. But yeah, changing the ECU is indeed a lot easier.

marjon said:

?? Why?

J

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Bearing in mind I have never even seen a 4.6, if I remember correctly from the manual, the auto box ECU on the 4.6 is CAN BUS and has parameters that have to be reset for a re-learn when fitted to a different box.

ar1g3 said:

Thanks already!

The reason I would prefer the sensor is that I need to open the gearbox anyway for a filter change, and with a used ECU you never know what you'll get. But yeah, changing the ECU is indeed a lot easier.

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I have been out and re-checked the sensor readings. I'm a bit embarrassed to find I have a broken lead that goes open circuit at certain angles on my DVM which resulted in the readings I gave you. The re-test shows 307 ohms both ways round. sorry about that.
Have you checked from either pin to the auto box metal work?
Chasing a fault on my auto box I swapped the ECU with no problem. It didn't cure the fault though.

Datatek said:

Bearing in mind I have never even seen a 4.6, if I remember correctly from the manual, the auto box ECU on the 4.6 is CAN BUS and has parameters that have to be reset for a re-learn when fitted to a different box.

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I thought the Can Bus was Range rover, not just the 4.6 (at a certain year) but that basically the Hp22 was the same electronic control as the Hp24 and also has the learn function.
But willing to read a bit more on it when I have time .

J

Datatek said:

I will do the measurement again tomorrow. Swapping the ECU is a heck of a lot easier than replacing the sensor, plenty available on the web and not expensive. Plug & play except for the 4.6.

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The P38A GEMS gearbox ECU is just a plain swap. Nothing else required. Not tried with a Thor yet.