Thanks for sharing that 159Kid, I don't suppose you know the fault codes which were generated ?( I guess you would have said what they were anyway but no harm in asking) It would be nice to know too, when did you get the EML warning ? Was it at startup, slow running or under hard accelration ?
If I were in a similar situation as you (and please note that this is all purely my own specualtion/fantasy) I would have left the sensors in place. A remap is only affecting the software which reads the sensors. If the remap is able to ignore sensor inputs when the sensors have been disconnected then it ought to be able to ignore them in situ too. If the problem with having sensors in circuit is that they provide an output even when the engine is not running, just unplugging them resolves the issue. So, I would have just kept the hollow dpf casing and disconnected the sensors if i couldn't leave them connected. The empty dpf is effectively a bypass pipe already.
An error code P0401, which is normally an EGR low flow code, is also listed in many DTC lists as 'DPF/EGR low flow'. Again though,without knowing your exact error code we won't know, but could the fault have been the same as my EGR one I got a couple of days ago, because I hade an orifice plate in the EGR circuit ? I cleared the fault and, full of good intentions, I meant to remove the plate. But I don't have any error codes today...it could reappear in a few days I suppose, so I will fix that at some point. I'm going on a 140 mile round trip today so it would be nice to get a fault code !
Anyway, the behaviour of the pressure sensors is that they output a linear voltage, as you might expect them to. The higher the pressure, the higher the voltage. So you might expect that at zero pressure (ignition on but engine not running) that the sensor would produce 0V. In fact, they produce about 350mV or a voltage in that sort of ballpark, for 0mbar pressure.
The reason for this, (and it's the same reason why many industrial sensing systems use 4-20mA signalling), is because it makes it easy to detect if you have a broken wire or a bad connection, or if the sensor has failed. There must always be a minimum signal level to validate the circuit before the equipment is started.
When you remove a sensor from the dpf , but leave it connected, it will still produce a voltage which means it is present in the circuit, so that when the ignition is turned on and the power on self test, POST, functions are run, it finds a sensor giving about 300mV output and then declares it has a valid sensor.
If you remove the sensor from the harness completely then the POST test declares an invalid sensor (because the voltage is too low) and creates an alarm. Unless, when remaping, the memory location of the alarm signal has been cleared.
This video Diesel particulate filter fix. - YouTube
Is the detail about how the differential pressure sensor, DPS, on a Volve V50 was defeated, allowing the dpf to be drilled out without error codes. For the sake of a potentiometer bought from Maplins, it is quite a good solution, as long as it works.
You can see that all it does is provide a 0.35V feedback to the ECU in place of the DPS. (Read the video notes and you'll see this has been revised to 0.37V)
Already having potentiometers to hand, before I drilled my DPF I searched in the engine bay for the DPS and thought it would be easy just to follow the 2 pressure pipes from the DPF back to the DPS. My intention was to see if I could bypass the working DPS with the potentiometer.
If I could drive the car without receiving error codes when the DPS was disconnected and bypassed, that would mean I was free to drill out the dpf, because the ECU has validated the DPS. I would have waited long enough to go past the point when a regen kicked in. I was going to drive for a week or two with the DPS bypassed by the potentiometer and monitor the fault codes regularly. With no codes after a couple of weeks I was going to remove the DPF and drill it through.
But as we now know, I have the functionally simpler DPF monitoring system. I have a bunch of strategies which I wanted to try though. An op-amp circuit could be used to multiply the pressure signal output if required, costing pennies. A zener diode and resistor could produce a fixed minimum voltage (similar to using the potentiometer). And if the worst comes to the worst a small circuit to create a substitute pressure signal which increases proportionally with the engine revs, would also be simple to make, also costing pennies too.
( I think the ECU has variable voltage output dedicated to rpm on one of it's pins, actually. I'ld need to double check that though)
So I had all these solutions and wasn't able to validate any of them, or even need them. However, I'm not going to buy a 2.0 just to play with,
. The theory is good though. For anybody looking at this seriously it is pretty harmless to try out. The DPS has 3 wires, 0V, 5V and o/p. The output should have a baseline minimum at 0mbar (350mV seems standard) and it rises by, say, 10mV per mbar (unvalidated but at lower pressures is probably reliable)
I was going to start off with a 10k resistor in series with the o/p signal, just for protection because of the unknown ECU input impedance.
Probably not the best idea if you don't work with electronics on a daily basis, but it seems a lot of Alfa drivers are a cut above the rest, on average, and there'll be a few EE's here
Thinking about that smoky car, 159_kid, there is a saying that 'The poor man pays twice' - He pays once to fix the problem cheaply, and then he pays again to have it fixed properly. Lucky for you that you only paid once