What exactly is limp mode

[MGSheff]

2010 V70 D5 150k miles

I have a couple of dash messages which I am trying to fix unsuccessfully.
I think the car is in limp mode but I don't know if it's something more serious.

What exactly is limp mode and what does it do to the car?

My car lacks power and it won't rev over 4000rpm (actually about 3900rpm). I'm hoping it's not a problem with the turbo, I think I can hear the turbo spinning up as normal.

I think my next step is to connect it to VIDA
I have bought a VXDiag Nano but can't get the software working. If there is anyone in the Sheffield area that can help me get it working or has a working system that could be used (socially distanced, masks, hands face space, etc. I work in education and my employer has deemed my work on site as essential so I do have to leave the house and use the car).

[Whippy]

Limp mode is where the ECU detects a problem either with the engine or transmission and automatically reduces power from the engine so the car will still 'limp home', the original fault could be anything. However, although the only answer is as you surmise a proper scan it's always worth just checking around to see if there's something obvious, in my case a plug supplying data / power to the turbo had loosened. Good luck.

[Laird Scooby]

Just to add to Whippys explanation, if the ECU detects a dead/malfunctioning sensor it usually ignores that sensor and uses a preset value and switches to a preset map (Limp Home map) for all fuel/ignition related settings that usually give some scope for fine tuning by the ECU but not much and some small amount of cold start control but for the most part, usually assume ambient air temperature of 20C and engine temp of 60C so won't be as economical or powerful as normal and in some cases will restrict power output and/or engine speed range.

First thing to do is read the codes to find out what area the fault is in - that isn't always the problem though.

For example, on some 7/9xx models, it will show either a MAF or AICV problem during a non-start situation when the in-tank fuel pump has failed. People then assume (wrongly) the problem lies within the MAF or AICV and spend buckets of £££££ on replacements only to find it still won't start.

The point here is until the engine starts, neither of those components have any real bearing on the fuel/ignition settings. The ECU expects feedback usually in the form of engine rpm changing but to do that, the engine has to be running. As it won't start due to a failed fuel pump, what the ECU is expecting to see from the MAF and/or engine rpm sensor doesn't happen it assumes the MAF, AICV or something else is faulty - it has no way of recognising a failed fuel pump and the designers of the software were only given "perfect" parameters to use for the program so didn't even know the fuel pumps could fail.

You see why this throws "red herrings" into the mix!

[griston64]

Originally Posted by MGSheff

2010 V70 D5 150k miles

I have a couple of dash messages which I am trying to fix unsuccessfully.
I think the car is in limp mode but I don't know if it's something more serious.

What exactly is limp mode and what does it do to the car?

My car lacks power and it won't rev over 4000rpm (actually about 3900rpm). I'm hoping it's not a problem with the turbo, I think I can hear the turbo spinning up as normal.

I think my next step is to connect it to VIDA
I have bought a VXDiag Nano but can't get the software working. If there is anyone in the Sheffield area that can help me get it working or has a working system that could be used (socially distanced, masks, hands face space, etc. I work in education and my employer has deemed my work on site as essential so I do have to leave the house and use the car).

I think I remember reading that a clogged fuel filter is a common cause of limp mode on D5 engines. Do you know when it was last changed ?

[SwissXC90]

Originally Posted by griston64

I think I remember reading that a clogged fuel filter is a common cause of limp mode on D5 engines. Do you know when it was last changed ?

And a broken charge air pipe
And a clogged DPF filter
And failled DPF sensors
And failled MAF sensor
And...

[MGSheff]

I serviced it in October and replaced the fuel filter.
I have the soot filter message and have had a couple of hour long journeys to attempt to clear the DPF. The soot filter message is still there.
I did wonder if the EGR valve and inlet tract was clogged so I tried the cleaning method with the EGR in place (disconnect inlet pipe, engine 2000rpm, spray full 500ml can in short busrts) it made no difference.

[Laird Scooby]

Originally Posted by MGSheff

I serviced it in October and replaced the fuel filter.
I have the soot filter message and have had a couple of hour long journeys to attempt to clear the DPF. The soot filter message is still there.
I did wonder if the EGR valve and inlet tract was clogged so I tried the cleaning method with the EGR in place (disconnect inlet pipe, engine 2000rpm, spray full 500ml can in short busrts) it made no difference.

The big clue is the soot (DPF) filter light, that will restrict your power!

I take it you kept the revs high and the gears low during your hour long journeys in an attempt to clear/revive the DPF?

You may have a duff DPF sensor, might be an idea to find a DPF recovery specilist near you and have the DPF cleaned and the sensor checked. I know on petrol engines, Lambda sensors have a useful life of 10 years/100k miles, whether similar applies to DPF sensors but given recent experience of a friends diesel throwing similar problems i'd suggest it does.

[Simmy]

dont drive it if you have a dpf that wont re gen it will throw a tcm message and will result in a limp mode where your car will be so restricted it will only do 30mph get mobile dpf company to test and fix your dpf problem they also carry top quality diagnostic equipment and will clear all your existing codes and tell you where your fault lies. good luck. iv also been down this road with these problems. all fixed now.

[MGSheff]

Thanks for all the helpful advice guys.
@simmy, it does get up to motorway speeds. My first attempt to clear the DPF was 1 hr on Mway at 2000rpm. No success. Second attempt I added DPF re-gen fluid to the tank and 1hr on Mway at 3500 to 4000 rpm in 3rd gear (60 to 70 mph).
Third attempt this afternoon, still with DPF re-gen fluid in tank, on driveway while working in garden, 1 hr at 4000rpm.
Still got message on dash.
Surely that has put enough heat into the DPF to clear any blockages. So I'm favouring a sensor problem as others have mentioned.

Still would like to get it connected to a working VIDA.

[Tannaton]

Originally Posted by MGSheff

2010 V70 D5 150k miles

I have a couple of dash messages which I am trying to fix unsuccessfully.
I think the car is in limp mode but I don't know if it's something more serious.

What exactly is limp mode and what does it do to the car?

My car lacks power and it won't rev over 4000rpm (actually about 3900rpm). I'm hoping it's not a problem with the turbo, I think I can hear the turbo spinning up as normal.

I think my next step is to connect it to VIDA
I have bought a VXDiag Nano but can't get the software working. If there is anyone in the Sheffield area that can help me get it working or has a working system that could be used (socially distanced, masks, hands face space, etc. I work in education and my employer has deemed my work on site as essential so I do have to leave the house and use the car).

There can be several different "limp" modes... some better documented / understood.

If you don't have any lights or errors on the dash, but have limited rev range, it's likely to be the temperature sensor on the CAT or DPF. VIDA will confirm this, generic code readers tend to make the situation more confusing with a generic message such as "temperature sensor bank A" etc. This is one situation where having the proper Volvo (or compatible) gear is essential or you are likely to be in expensive and time consuming poke and hope diagnosis.

If it is the temp sensor - they're about £100.