D40 dpf sensor parameters

[ash050]

G'day,if been reading the forum for a while now with lots of things learnt.if had the dreaded d40 auto dpf problem and have just purchased the chip it delete pipe,was wondering if anyone could tell me what resistance the two sensors in the dpf are when at normal operating mode.
Cheers andrew

 

[DieselSmart]

are you going to solder in a resistor to stop the sensors from seeing to much air going through them?

 

[ash050]

I was Gunna try that,as one of the sensors melted when the dpf packed it in.has anyone tryed this.

 

[DieselSmart]

I don't think it will work. If you have a constant voltage it will cause the car to run too rich or too lean. They are basically an o2 sensor and depending on what air it's seeing it will add or reduce diesel...

If it were to see a constant voltage, it might be alright at 100k's an hour but on idle cause insane diesel rattle and vice versa..

Have you found out how much one of these sensors would be from Nissan? get a part number from nissan and ring repco see if they have a compatible product for about 1/4th the price...

 

[ash050]

Yeah was thinking that the o2senser was the brains of the operation and the other two were measuring differentiation of pressure via temp just to clean the filter?ill have to do a bit more research.???idears

 

[Old.Tony]

There should be 3 sensors in the DPF. The first is the Heated Oxygen Sensor (HO2S) which is a definite no-no with regards to replacing with a resistor. Minor fluctuations in fuel rail pressure are measured by this sensor and the results compared in the ECU. Unexpected results (eg a flat line!) will send the car straight into limp mode. This sensor determines when it is safe or appropriate to squirt fuel into the exhaust stroke so that the DPF and CAT can have some nummy diesel.

The other two are pressure sensors that measure the exhaust pressure before and after the DPF's filter medium. If there's a significant difference in reading, it means there's some restriction offered by the DPF and thus a burn is needed.

This means you cannot replace one with a resistor (thus making it 'static') and leave the other as a real sensor, as Dieselsmart says. The ECU will go nuts trying to sort out how the pressure on the far side of the DPF is higher - it might result in a negative, which if not handled properly by the ECU's software could cause it to crash.

You would have to replace the sensor. I'd try Niss4x4 in Vic and see if they can get you one from a wreck.

 

[ash050]

Your right its probably the best option to just replace it.just to get my head around it thou from what you were saying the o2senser is giving the ecu the right fuel trim and the pressure sensers only measure for a difference so if I did put a resister in both it should work in theory or do they change any other parameters I.e during warm up or are they constant if it's all working well?cheers for the help by the way guys.

 

[Old.Tony]

I see what you're suggesting - replace both pressure sensors with resistors.

That might work, I've no idea - I've not tried it myself and in all the discussions I've had or read on these sensors I've not seen or heard of anyone else trying it - if you cut the two sensors off - or better still, put the resistor across the plug - and replace them both with identical resistors (use an accurate multimeter to make sure) then you are breaking new ground.

I don't think a lot of current is passed through the sensors and the voltage won't be too high - it's probably only fed 5V.

 

[mgermasi]

Hi Ash050 and OldTony
I believe both sensors as most sensors they should have + - & signal back to the ecu or + straight back to the ecu hence what about if you get the + and split it to feed both signal back to ecu? That way you'll have zero differential.
Questions:
)- Does the ecu wants to see zero differential?
)- Does the ecu wants see a small constant differential?
)- Does the ecu wants to see a variable differential directly proportional to the RPM?
)- Would it be easier to change ecu to same model without DPF? ie 2010 or 2012?

Cheers

 

[Old.Tony]

First, I've no experience with changing ECUs. The ECU interacts with other vehicle modules and you'd have to be sure that not only are the other modules compatible with that ECU, but that the signal ranges are compatible.

As for what the ECU is looking for precisely between those pressure sensors, I'd say that the closer they are to each other the happier the ECU will be. Some people have placed the two pressure sensors into a single small pipe (one into each end of the pipe) and that's apparently worked.

If they were really, really pedantic about it they could monitor variable fluctuation rates, depending on MAFS input, throttle position, engine load, boost pressure and coolant temperature - which would result in your 3rd option. I can't see them going to all that complexity just to determine whether or not the filter medium between the two sensors is blocked enough for a regeneration cycle. Then again, they did add (post 2010) an EGR sensor to make sure there's exhaust gas flowing through the EGR valve, so they CAN be pedantic if they want to!