MixManSC indeed all data useful, good for inspiration.

A while back I made a formula to calculate PSI for any given sensor O/P, from this an output of 0.22V corresponds to 34.6 PSI, very close to the 35 psi figure.

Regardless of the reading, one would expect the ECU to open the inlet valves, measure the air-bag pressures, turn the compressor on and adjust the ride-heights accordingly.

It appears though, the compressors are running with the inlet ports “closed” at least for some of the cycle, otherwise the rear would be lifted. If true "How can this be?"

One might expect a DTC to be raised if an inlet valve fails to "Open" either "C0716 Left" or "C0177 Right" but not 100% sure this will happen.

Then there’s the question of solenoid wiring, perhaps they are crossed over or in some way wired incorrectly?

FYI a solenoid valve draws around 1.4A @ 12V on the bench and has a DC resistance of 8.2 Ohms, so your new inlet valves could be measured with a meter to confirm they are the same (should be )

Also the Tech2 can operate Left & Right valves individually and at the same time show the "Total Valve Current" and corresponding "Height Sensor" voltage as it falls. It might be worth confirming both left and right valves operate correctly. Interestingly, the Tech2 shows the "Total Valve Current" as approx.350mA, suggesting the valves are pulse-modulated.

If the vehicle levels correctly (which can’t be by accident) and is otherwise operating normally (except for the relief valve operating)then the over-pressure might be caused by the compressors being "too good" so to speak. Perhaps there is always some "continued" compressor activity even after the inlet valves close, and as the new compressors are so good, pressure quickly builds-up and hence the problem. It could come down to peak pressure, capacity and flow-rate. An in-line pressure regulator could be used to set the maximum pressure, rather than using a pressure relief valve (or try one compressor to see if that helps - you would need to ground the over-temperature input on the one removed)

So it's a bit more food for thought here, but it still doesn't explain why the pressure is stuck at 35 psi, perhaps the new sensor is a completely different animal?

You could always unplug the inlet valves, pipe-in a little compressed air and watch the pressure reading on the Tech2. I’m trying to set-up a demonstration of this, but something like a car tire is needed to act as a reservoir otherwise the pressure builds-up too quickly, a bit like your hoses bursting which is what made me think.

 

maybe if you can get a hose to Schrader valve adapter onto the block disconnecting the compressor air line directly connecting the fitting to the pressure sensor block then you can use a bicycle pump to test the pressure sensor directly. then compare what the sensor is reading to what the bicycle pump pressure gauge says. then maybe you can see if it is a bad sensor or wiring.

 

bronxteck great idea, but you got me thinking, the Tire Inflator already has a Shrader valve so why not hook-up the Tech2, monitor the pressure and pump air back-through in reverse?.

.... progressing on "Why not just turn the compressor on?" sounds obvious right!

So it does work, as follows (at least it does on an 2005):-

1. Ignition On - Engine off.
2. Tech2->"Air Suspension" -> "F2: Special Functions" -> "Compressor Test"
3. Scroll down to show "Rear Leveling Air Press" 41 psi (ambient in my case)
4. Press "ON" to start the compressor then watch the air pressure increase - job done.

Just one thing, the compressor test only seems to run once per ignition key cycle i.e. 1 start, stop then no restart until ignition key recycle.

During my tests the "Rear Leveling Air Press" went from 41 psi to 58 psi (stopped 5 seconds after reaching that point) so good enough to prove it works.

 

Hi all, I am back on line now, I had some time off away from everything.

Thank you all, your thoughts and suggestions all sound good and I will attempt to work through them all this weekend and report back next week.

Reading through some of your comments I would like to add some further information which may assist diagnosing the problem.

1. I have already fitted a tyre (tire) pressure meter to the fill valve and running it manually with the switch which bypasses the controls for the solenoid valves, I can get 250 psi which will be fantastic when pumping up tyres in the field.
2. I have also tested it when the engine is first started, the pumps are both running and it will do the same as above and the pressure reading is still 35 psi and no valves open, even when the *** end is low and requiring air to lift to the correct ride height. And for this reason I fitted the pressure relief valve which blows off at 140 psi a few times until the compressors cycle off.
3. This may explain sometime. To over come the above problem, I manually run the compressors with the tech2 to about 3 volt and then stop the compressors.After a few seconds the exhaust valve (my modified version) blows off air as the left & right solenoids independently open & close until it stops on the learnt ride height of approximately 2.6 volts. Yes I have been able to cancel and do a re-learnt of the system without any issues. However as I drive and park the car on different angles, if one side is too high it will blow off some air, however when I level out the car one side may now be low and the compressors will run but the solenoids will not open. I am viewing this on my tech2 and driving and it still reads 35 psi
4. Another thing to point out, my new compressors do not have a third wire to monitor over temperature, they have an internal thermal relay that protects the motor from over heating so I have already earthed both senor wires.
5. Oceanbrave, I hear what you say about the compressors being too good, however they take about 10 seconds before building up high pressure and again monitoring via the tech2, I still have 35 psi, so I don't think it's a issue with too much pressure. My understanding is when either side needs air the compressor will start and build up pressure to a set point obviously higher than the pressure in the air bags before the valves open. I don't know what this pressure set point is but I assume it's higher than 35 psi otherwise my valves would open. From memory when I disconnected the air compressor system and pumped up manually I only needed about 25 to 30 psi depending on the weight in the car and the ride height I wanted.
6. I think the 35 psi reading is the problem, either a dud sensor (unlikely) as it's the second one or wired incorrectly. What would happen in the control circuit if I have 1 & 2 backwards ? Is it worth swapping them around or will that cause more issues and burn it out the sensor if in fact I have it wired correctly?

I will work through all your suggestions over the weekend and report back. Thank you all.

PS, After I resolve this issue I will fill you in on my latest successful project, I have fitted into my 2005 H2 an LSA 6.2 litre supercharged engine (430Kw) coupled to a 6L90e transmission and still running all factory cluster, ABS, cruise control, air conditioning, etc. The only factory thing not working is the gallons per mile or in my case litres per 100 Km's.

 

Somewhat off and might not be good to add to the equation at this point.... but on mine I always wanted to look at a way to tie an air tank into the system. That would serve a few purposes, one to be able to add something like an air horn, other to add a port to use air tools, and finally the compressor would really then only need to run the air tank up to say 120psi with the low cut in at maybe 80psi. Then when the air bags need to adjust that valve would then open to the tank pressure and adjustment would be very rapid. I have an air suspension setup on a custom truck I have that works in that manner but it is an aftermarket system (Air Lift).

 

MixManSC,

I have also added a pressure tank onto my system as I have installed an ARB front air locker diff and air horns, but it doesn't work like a conventional storage tank setup like on your truck as the H2 computer doesn't think that way. When the compressors stop working after lifting the air bags, it blows off any excess air in the lines because it can't have pressure in the valve block because it exhaust air through it to lower the air bags when leveling out the car. If there was a tank there with pressure all the time feeding into the valve block you would never be able to lower the air bags.

I have installed a small 3 litre tank with a non return valve fitted to it at one end and a short manifold at the opposite end which I fitted solenoids too for the air locker diff and the air horns. The supply line is tapped off the line to the manual inflator valve. You don't need much air to engage the diff, however if you are a driver who is on the horn a lot you have a problem because 3 litres will not last long in my set up.

I fitted the tank with a 110-145 psi pressure sensor which I wired in parallel with the manual inflater switch which provides air to the tank and not the air bags when ever the engine is running and the car in park, so basically on every start up it will fill the tank if it's dropped lower than 110 psi. I know this is not a perfect system but it's all I need for the front air E locker diff, the horns are just for fun.

Oceanbrave, this is disconnected at this time until I resolve my other issue.

Another point I forgot to mention yesterday was my manual ride height button in the car doesn't work, the light blinks, however the valves don't open to lift the car. I can't remember if the compressors are running at this time or not. I can manually via the tech2 trigger the switch and the light

 

Hmmr what you say in your comments (3) & (6) makes perfect sense and I concur that 35 psi is likely to be the root cause of the problem.

It's hard to say what the consequences (if any) of a reverse polarity would be, but I've devised a way for you to discover the pin assignment "non-destructively" however as mentioned before, your new sensor may be a completely different animal so to speak.

You'll need a multimeter with a "Diode Test function" (most meters have this feature)

Most electronic automotive devices incorporate a protection diode connected directly across the power pins to guard against reverse-polarity voltage spikes, often generated during cranking.

Below is the pinout of the old sensor, I have annotated the pins and shown where I believe a diode is connected:-

The exact values may vary depending on the brand of your meter, but changes with lead will indicate which is the 5V pin (hopefully)

I measured an original sensor on the bench using two meter brands (M1 & M2) on "Diode Test" both similar results, as follows:-

Black Lead Red Lead M1 Value M2 Value
Pin 2 Pin 1 1.826 0.976
Pin 1 Pin 2 0.599 0.519 <--- Black lead indicates the Power is Pin1, Red Lead indicates the 0V is Pin2
It doesn't matter which pins are chosen, the lowest reading only occurs for the power pins, so for above Black identifies +5V, Red 0V pin and Signal pin is the remaining pin.

To explain this, the diode test will cause the diode forward conduct when its anode is positive, this can only happen in one direction ( the meter shows the diode's forward volts drop 0.5 to 0.7V for silicon) When connected correctly the diode is reversed biased allowing the sensor to function normally.

For reference on Ohms test the sensor measured 6.3 KOhms across its power pins in either direction and approx 185 KOhms from the Signal pin to any other pin
both M1 and M2 gave similar results.

I can't 100% say is this test will work for your new sensor, however the diode test is safe and will do no harm to it.

I'd say the chances are good this test will identify the pins for you. Also from the above I'd say there is a chance the sensor's power pins are either not connected to +5V or it's defective.

By the way the ECU limits the +5V Ref current to 275mA , so one would expect for a reversed sensor the "Height Sensor Current" should show a higher value than 17mA (at least for a while) or the ECU would shut-off the O/P completely.

Again this is quick and easy test to try (it would be good test your old sensor if you still have it)

 

Oceanbrave,

I had an opportunity this afternoon to do some testing before the weekend and I thank you for your helpful explanation and photos with step by step procedures.Even I understand it.

I still have my old solenoid block with pressure sensor and I did your suggested diode test across pins 2 & 3, photo below and my reading was 0L, I assume very low or 0, I reversed the wires and had the same result, 0L.
From pin 3 to 2 was 195 Ohms and between pins 3 and 1 it was 198 Ohms.
Across the power pins it was 6.327 Ohms






I did the same test on my new solenoid block pressure sensor with the following results;
Diode test across pins 2 & 1 was 0L and reversed was also 0L, exactly the same as my old pressure sensor.
The Ohm test across pin 1 & 2 was 56.4 Ohms and from pin 3 & 2 was 34.5 MOhms and between pin 3 & 1 was 34.5 MOhms.

I installed the compressor kit back into the car with the compressors unplugged and the sensor unplugged with the ignition fully on but engine NOT running.
With no jumper installed I had a stable .02volts and 29 psi open to atmosphere. So it does move off 35 psi.
Jumper wire between pin 3 & 1 was 0 volts
Jumper wire between pin 3 & 2 was 4.25 volts

 

OL means Out of Limit or no connection.

 

Hmmr indeed OL is Over Limit or Out-of-Range.

So looking at your Fluke it has capacitance ranges and in the top right it says nF (nano farads) could it have been on Capacitance and not Diode test?

Presumably pressing the Orange function key selects the functions in orange characters?

I mention this because Fluke are the best meters and usually all work in the same way.

To prove it works, grab any regular diode and test it with the fluke, the diode testing is a bread-and-butter function used in semiconductor diagnostics.

The reading displayed when forward biased is the actual Forward Voltage drop (VF) of the diode junction with a constant current of 1mA passing through it, the value is 0.7V for silicon and 0.2V for germanium.

Might be worth checking.

I'm out at the moment and will look at your results in detail later, but OL seems a bit odd, not what I was expecting.