P102B

[user 50884]

This is for a pathfinder r51 2010 not a D40 but still YD25 140kW engine euro 4 I think (?)

It will runs great for up to 200kms but will all of a sudden through p102b code and drop in power. Normally it fixes itself just by restarting the car.

Any ideas? Seen in other threads people suggesting boost sensor or high exhaust temp and that unblocking egr may help?
Any other suggestions?

Cheers

 

[Old.Tony]

Sounds like a suction control valve. Is it hunting at idle (not steady, but a noticeable regular variation in idle speed) ?

Try this: with the engine warm, at about 60km/h accelerate hard. Does that cause the problem to reoccur? If so, it's more likely to be the SCV (it's a component on the fuel pump).

First thing to try (which is never a bad thing to do anyway) is to either put a bottle of fuel injector cleaner in the tank or use some Liqui Moly Diesel Purge (instructions on the can, but YouTube videos also available).

This may or may not have an effect, especially if there's scoring or other damage on the SCV. This is when you could pull the SCV out and inspect it - two Torx bolts and an electrical connector and the SCV is free. Any sign of scoring, dark lines or pitting in the surface would mean replacement may be the best option.

 

[user 50884]

No it idles perfectly, even when it plays up (kind of limp mode) starts to thorough a bit if black smoke.

I try to put my finger on when it actually happens, but it seems to just be randomly..

I took the scv out gave it a clean but couldn’t see any scoring.

Haven’t tried any diesel additives but will give it a crack.

I’ve noticed that the engine oil level is a little above max level, and the oil seems kind of thin. I wonder if diesel is getting in to the engine oil..

Apparently the code is for high exhaust temp?

 

[Old.Tony]

Not exactly. It indicates that the pressure in the exhaust is the same as atmospheric pressure. The manual describes this as "exhaust gas pressure sensor air leak" and goes on to define that as meaning equal pressure inside and outside the exhaust.

The fix - according to the manual - is to examine the complete exhaust system looking for leaks. If yours has a DPF this won't be as simple - up to the DPF you'll see black sooty streaks coming out of any leak in the exhaust, but the DPF catches soot and you'll have to find another way to detect leaks - although a leak large enough to cause this error ought to be easy to see!

Chances are though that it's a sensor issue. The exhaust gets really hot and temp fluctuations alone can cause failures, let alone high temps if the car's had to climb steep hills. Check the sensors on the exhaust - particularly their electrical connections. Just for kicks, connect a wire from the exhaust up to the battery negative and see if it does it - the exhaust is supposed to be grounded but age and wear can end that. If there's no ground, sensors using power will be quite erratic.

 

[user 50884]

Cheers for the detailed answer mate.

I’ve only just bought it. It looks like the egt sensor has been replaced already as it has a “wrecker writing” on it.

It’s tuned with an after market exhaust. So no dpf or cat. One of the first thing I noticed was a loose ground wire to the exhaust. I did put it back on but now it has come loose again. I’ll put it back properly this time and extend the ground wire so it doesn’t vibrate loose again. Hopefully it will fix it!

 

[user 50884]

Put the ground back on the exhaust. 100kms later and p102b is back.
After driving 5min on flat road, all of a sudden it reduces in power remarkably.
Turn off the car and start it straight away and she runs like a dream again..

I do wonder I the tune is playing tricks with the ecu or something along those lines..

 

[user 50884]

The pressure in the exhaust is the same as atmospheric pressure.

How is this defined? is there a atmospheric sensor? Or does the egt simply know what that pressure is? i.e just a set value on the egt sensor will trigger the code?

 

[Erick]

Doubt the exhaust is at atmospheric pressure. When ur boosting to 15/20 psi and then heating all that to 500 degrees or more and sending it back out through a pipe, it’s not at atmospheric pressure. Sounds like a Chinese translation, ie someone does not know what they are talking about. But if it has a sensor then that’s a possible problem in itself.

 

[user 50884]

Would it be wise to disconnect the egt sensor for a while to see if the issue disappears?

 

[Old.Tony]

Would it be wise to disconnect the egt sensor for a while to see if the issue disappears?

Disconnecting the EGT sensor will likely cause a check engine light (malfunction) light to come on, probably with a code relating to the DPF.

As for atmospheric pressure, it may be able to figure that from a combination of boost sensor and the MAFS (temp + flow rate + turbo commanded + resulting pressure = original pressure). It might even just be a function of the newer MAFS.

 

[user 50884]

Thanks Tony.

I think that injector cleaner funny enough may have solved the issue… didn’t think these products would work.

After pouring it in it started to smoke and go down in power a lot more frequently. But after using up the tank and driving on just diesel it seems to have gone away..

I don’t want to take out the win in advance but it certainly is looking a lot better.

Fingers crossed

 

[user 50884]

Gah the issue is still there..

A question about the idle, should it be dead steady?

Mine does fluctuates a little bit. Around 50rpm.

It doesn’t fluctuate quickly. It sits on a steady idle for maybe 30 seconds the it goes down for 30 seconds then back up again and continues like that.

Kind of like the ac compressor would be going in and out.

One thing that’s changed since adding injector cleaner is that it seems to loose power every time now on cold start. If you get it up to temperature then restart the car she’s all good.

Worth pulling the injectors out?

 

[Old.Tony]

There's always a small fluctuation managed by the ECU to ensure that the exhaust sensors are working and measuring the oxygen levels correctly because the ECU needs to feed reductant - fuel in our cars, AdBlue in trucks and some passenger vehicles - to the catalytic converters. The ECU will drop the RPM by a near imperceptible amount, which should correspond to a small change in the exhaust. This should be quite difficult to detect by listening but a digital tachometer will show it.

If you can hear the change, we call this "hunting". I can't think of any reasons other than the SCV that cause this - perhaps someone else might have some more insight.

 

[user 50884]

Found the issue, the egt pipe that mounts to the turbo was loose.