D40 Limp mode and DPF light

whazp · Oct 19, 2019

Hi All, hoping for some advice. Ive got a 2011 D40 (Thai built) Auto Navara.

The car had been stalling after starting frequently and was getting worse. Performance & fuel economy had been bad for quite some time. I Noticed black smoke coming out the back of it whilst under acceleration too. Anyway the wife was driving the car when the DPF light came on & then went into LIMP mode shortly after. Managed to get the car home.

Checked the codes and got a P0403 indicating a problem with the EGR valve. No worries i replaced it with a new one and also swapped out the SCV valve at the same time just to be certain that wasn't causing any problems.
Cleared the fault code for EGR and tried to start it back up. Still stuck in limp mode. Next tried to hard reset the ECU by disconnecting the main battery overnight to get it out of LIMP mode (tried pressing on pedals too). That didn't work. At this point the car keeps cutting out after i start it unless i keep the revs up and its stuck in LIMP mode.

The DPF light is still on & after some research it looks like its the likely culprit.
I can't get the car to do a DPF burn while its in limp mode though.

I was going to buy a Foxwell NT650 to force a DPF regen as the unit only costs $280 to buy and it would be handy for other uses too.

A couple of questions though.

I was wondering if anyone has been able to force a regen using one a Foxwell NT650 - it claims to be able to do it on Nissan models. Would it even be able to force the DPF regen when the car is in limp mode?

Ive seen people cleaning their DPF's with high pressure water hoses. If i cleaned the DPF manually would the car take itself out of LIMP mode once it senses the DPF is clean? Has anyone cleaned their DPF like this?

Any other suggestions? I can't really afford a new DPF or what the local service techs charge around here to fix these types of problems.

Old.Tony · Oct 20, 2019

Welcome to the forum.

The limp mode you have is likely to be enforced by the DPF issue, which seems to be a separate routine in the ECU to normal error handling. With that said, if the DPF error is resolved, the DPF routine seems to be able to clear itself after some driving. There are two sensor issues with the DPF:

1) Pressure differential across the DPF, measured by the black sensor on the guard near the ABS unit. This is not a common failure point.

2) Temperature sensors front and rear. These are a known failure point (my own failed, in precisely the same way yours did). Mine was resolved by knocking out the guts of the DPF and replacing the sensors with units provided by auggie (a user on this forum, send him a PM).

I've never heard of someone washing the DPF. It would work, the lattice within is quite strong and should not be damaged by moisture (the engine produces water as part of combustion anyway).

Resetting the ECU doesn't always clear higher-priority errors. You need a machine that can talk to the ECU for that, the errors are stored along with the distance travelled since the error occurred. I paid a local mechanic $50 to clear the code (that was for his time) to clear the code but because I hadn't fixed the DPF (those temperature sensors) my error came back.

The problem is that if you reset the DPF error and the light goes out but the problem still exists, it might try a DPF burn and still fail and bring the light on again. With a machine of your own, you stand a chance of resetting it continually to keep yourself going but that's potentially very annoying.

We're going on a 9,000km trip this Christmas and I hate to think that I'd have to stop every 50km to reset the DPF light then continue!

I have never seen a Foxwell device so can't offer an opinion on it. Forcing a regen is a different beast to resetting the DPF light - a forced regen takes some time, works the engine VERY hard and it's recommended to change oil+filter afterwards. If the temperature sensors are faulty, the forced regen might clean the DPF but won't fix the problem. You will have cleaned the DPF and you'll have a nice widget to fiddle with codes later, so not all is lost, but at that stage you might need to replace those sensors too.

In terms of spending money, you might be better with the Foxwell unit because it should be able to do a lot more than just force regens on a Navara and might just resolve your problem. It would be worth attempting the clear the error first, and take the car for a drive (it will attempt a regen approximately 200km after resetting the DPF error). That's when you'll know if you need to attack the car harder, or not.

whazp · Oct 20, 2019

Thanks for the advice Tony. Ive bought the Foxwell NT650 unit ($276 express posted from ebay). At least i'll have a decent scanner even if i can't sort out the problem.

Was hoping to reset the DPF code and then take the car for a drive to get it to DPF burn normally. If that doesn't work i'll initiate a regen. Ive got new oil & filter ready to change afterwards. I'll post the results in the forum.

Would a badly blocked DPF cause the car to stall whilst idling? I can't keep it idling at the moment unless i keep acceleration up. Not sure what else would cause it to stall all the time. Have replaced SCV which is the usual culprit.

Old.Tony · Oct 20, 2019

A blocked DPF could cause the car to stall, but if the exhaust isn't flowing well enough at idle, there's no chance it's going to be flowing well enough at speed so my guess is that it's something else. Perhaps a dirty MAFS? Only use electrical contact cleaner spray to clean this, and nothing else. I'm assuming you've already checked the air filter.

A leak in the fuel line up around the filter (any of the hoses, or the primer bulb) may also do this, and you won't be able to spot the leak because it's not fuel getting out, it's air getting in. You find the leak by squeezing the primer bulb and pressurising that part of the system. If you can squeeze it gently more than 4-5 times then there's a leak somewhere, it's just a matter of finding the seeping diesel. You should be experiencing difficult morning starts if this is the case.

Other than that, a sticky EGR valve is often the culprit but since you've replaced yours I wouldn't normally suspect it. You could always put a blanking plate in at the connection between the gold EGR tube and the EGR valve and see if that fixes it. Make it quickly from aluminium to see if it resolves the issue, or make it from 1mm or more stainless for a permanent solution. I made mine from 1mm stainless by tracing the gasket onto the stainless and accidentally forgetting the big hole in the middle, oh dear what will I do haha ... I did that several years and over 200,000km ago and have not had any dramas at all.

Diesels are rather simple. Give them fuel and air and they go. It's not your turbo, the turbo doesn't spin much at idle. It could be a dirty intercooler but you'd notice that at speed too.

There is a chance it's the crankshaft position sensor and the car's not getting the timing right, but you should notice this at speed as well, as a reduction in power.

whazp · Oct 20, 2019

Thanks, i cleaned the MAFS sensor about 9 months ago but i'll give it another go. Also ill try the fuel primer to see if there's a leak. Could also be dirty fuel or fuel filter too. Hopefully the scan tool works for DPF rege / reset.

whazp · Nov 9, 2019

Ok so the dealer has confirmed the DPF is stuffed. But they are also saying there is a fault code with the SCV valve?? I've literally just replaced it with a Denso genuine SCV valve. And it was replaced 12 months prior as-well.

I don't think the SCV valve is faulty with 2 replacements in less than a year and a brand new one showing faulty immediately. I think something else i causing the ECU to report it as faulty.

Does the SCV valve have a fuse somewhere that i can check? Would a faulty fuel pump or some other fuel issue make the ECU think that the SCV valve was faulty?

Thanks =)