mclarenaml
Member
Apologies if this ends up a bit of a tome, but I’ll attempt to fill in all the relevant (?) history.
The vehicle is a 2006 D40 Navara, with the 2.5 turbo diesel engine, and it’s done around 250000km The problem first arose in early 2022, and is triggered when the vehicle is under sustained load for a period. The vehicle is often used to tow a loaded horse trailer, and the problem typically happens with long, uphill, open road sections where there is high power demand for maybe 10 seconds or longer. Now that we know what triggers it, the fault can be created on demand. When the problem occurs, the vehicle has an instant loss of power, similar to limp mode, but power can be restored by lifting and reapplying the throttle. It is possible to generate the fault without a load, but is a bit harder, and doesn’t happen in normal use. Minimal faults were being logged, but I think I now understand why.
The vehicle was away from home when the first occurred, so was not handled by our normal garage. When they first looked at the ECU, they noted that there were MAP sensor and boost control solenoid faults present, but have no other details. They tested the supply and MAP sensor earth and all OK, but problem persisted. They replaced what was invoiced as a “41-540 Turbo Dies.pressure valve” (I suspect there is a typo there, as don’t know what this is other than it wasn’t cheap!), and installed a new boost solenoid sensor. I recollect that they also replaced something expensive, but were somehow able to return this after verifying it made no difference, but don’t know what this was. When the vehicle was returned, the problem was supposedly resolved.
But No! About 4 weeks later, it was given to our normal garage to do a full service, as a precursor to try to get to the bottom of this. They noted there was a boost sensor P0238 code present, but were not certain if this was historical. They were supposed to check/replace the fuel filters, but missed the pre-filter. They road tested the vehicle with live data running, and found around 200KPa of boost, which is at the upper limit, and possibly indicated overboost, but other than this they couldn’t fault it.
After another 4 weeks it was back again. By this stage we had figured out how to create the fault on demand, so expected there would be mass of faults logged, but they only found a single P0234 (another overboost code). They removed and checked the DPF. This time I was able to demonstrate the fault to them, and their suspicion turned to the fuel supply. They then “found” the pre-filter they had missed earlier, it was full of muck, so replaced it. At this point the problem appeared to have been resolved. That was June 2022, and the problem did not reappear for 2 years.
Mid way through this year, the problem reoccurred, and as before, it’s triggerable on demand, but really only evident under the load conditions mentioned earlier. It’s been back with a third garage, and after rechecking everything he can, he is convinced that the problem is the turbo itself. I admit to being a bit sceptical, particularly as replacing this without a smoking gun is an expensive hope.
To try and understand this better myself, I’ve got an ODB scanner running, and have been playing with generating the problem, and seeing what is logged. Even time I trigger the fault, I have a pending P0234 code logged, which will disappear after a period (supposedly after a restart, but in the Navara it takes longer than that – just seems to be based on a period without the fault recurring). These all indicate an overboost issue. I didn’t understand about pending codes earlier, but this presumably explains the earlier scenarios with no apparent faults being logged.
I feel comfortable that the ECU is detecting an overboost situation and is taking remedial action, but the question is why. I’d appreciate any thoughts, ideas, things that should be checked, whatever. I’m not averse to replacing a turbo, but would like something definitive to pinpoint this as the issue. I do have some questions though!
Andrew
The vehicle is a 2006 D40 Navara, with the 2.5 turbo diesel engine, and it’s done around 250000km The problem first arose in early 2022, and is triggered when the vehicle is under sustained load for a period. The vehicle is often used to tow a loaded horse trailer, and the problem typically happens with long, uphill, open road sections where there is high power demand for maybe 10 seconds or longer. Now that we know what triggers it, the fault can be created on demand. When the problem occurs, the vehicle has an instant loss of power, similar to limp mode, but power can be restored by lifting and reapplying the throttle. It is possible to generate the fault without a load, but is a bit harder, and doesn’t happen in normal use. Minimal faults were being logged, but I think I now understand why.
The vehicle was away from home when the first occurred, so was not handled by our normal garage. When they first looked at the ECU, they noted that there were MAP sensor and boost control solenoid faults present, but have no other details. They tested the supply and MAP sensor earth and all OK, but problem persisted. They replaced what was invoiced as a “41-540 Turbo Dies.pressure valve” (I suspect there is a typo there, as don’t know what this is other than it wasn’t cheap!), and installed a new boost solenoid sensor. I recollect that they also replaced something expensive, but were somehow able to return this after verifying it made no difference, but don’t know what this was. When the vehicle was returned, the problem was supposedly resolved.
But No! About 4 weeks later, it was given to our normal garage to do a full service, as a precursor to try to get to the bottom of this. They noted there was a boost sensor P0238 code present, but were not certain if this was historical. They were supposed to check/replace the fuel filters, but missed the pre-filter. They road tested the vehicle with live data running, and found around 200KPa of boost, which is at the upper limit, and possibly indicated overboost, but other than this they couldn’t fault it.
After another 4 weeks it was back again. By this stage we had figured out how to create the fault on demand, so expected there would be mass of faults logged, but they only found a single P0234 (another overboost code). They removed and checked the DPF. This time I was able to demonstrate the fault to them, and their suspicion turned to the fuel supply. They then “found” the pre-filter they had missed earlier, it was full of muck, so replaced it. At this point the problem appeared to have been resolved. That was June 2022, and the problem did not reappear for 2 years.
Mid way through this year, the problem reoccurred, and as before, it’s triggerable on demand, but really only evident under the load conditions mentioned earlier. It’s been back with a third garage, and after rechecking everything he can, he is convinced that the problem is the turbo itself. I admit to being a bit sceptical, particularly as replacing this without a smoking gun is an expensive hope.
To try and understand this better myself, I’ve got an ODB scanner running, and have been playing with generating the problem, and seeing what is logged. Even time I trigger the fault, I have a pending P0234 code logged, which will disappear after a period (supposedly after a restart, but in the Navara it takes longer than that – just seems to be based on a period without the fault recurring). These all indicate an overboost issue. I didn’t understand about pending codes earlier, but this presumably explains the earlier scenarios with no apparent faults being logged.
I feel comfortable that the ECU is detecting an overboost situation and is taking remedial action, but the question is why. I’d appreciate any thoughts, ideas, things that should be checked, whatever. I’m not averse to replacing a turbo, but would like something definitive to pinpoint this as the issue. I do have some questions though!
- Can this be caused by the turbo itself? I’ve read on this forum about potentially stuck vanes on these turbos which could presumably do this.
- I couldn’t find anything in the OBD sensors that gave me a direct turbo boost reading. Without this, how does the ECU come to an overboost conclusion? (there is a “Calculated Boost” sensor (or pseudo-sensor), but this seems to indicate the boost the ECU has requested, rather than what it has. This tops out around 1.5bar (150 odd Kpa), which seems about right for this engine.
- The apparent resolution two years ago by replacing a dirty fuel filter has me puzzled, as seems to indicate a totally different issue, whereas everything feels identical. I am wondering if there was already a marginal issue around the turbo, that fixing fuel supply issues simply masked for a period.
- If we do go the replacement turbo route, Nissan replacements are eye-wateringly expensive, and I’d probably just (sadly!) replace the vehicle. There are a number of aftermarket turbo’s around for these, many originating in China. I gather quality varies from rubbish to good! Anyone had any experiences with these?
Andrew
.. which is what u want !! u can also hold the top screw plus the round nut & nip up the round nut slightly with some pliars to ensure it never rattles loose and gives huge overboost one day 
