No Warning Lights

[taxi driver]

This is the 4th S80/V70 D5 I have owned. The previous 3 Each exceeding 300k without any engine problems and 43-45MPG . My latest V70 D5 2010 was purchased 3 months ago with 120k. Initially the car performed well despite lower than expected MPG (38). The first indication of a fault was occasional engine misfire at around 50mph. Just seemed to miss a beat, maybe once in 400miles. Never at motorway speed, normally when entering 50mph zone on motorway.
Then without warning after completing a 200mile journey and stopping for 5 mins a Soot Warning came up. OK thought Re Gen problem. Warning disappeared after 30seconds.
I booked the car into Volvo Specialists in Baldock the following week. They put it on diagnostics and nothing came up. Everything checked and with in tolerances. They suggested using premium Diesel. On the way home same engine misfire, just once. I have driven the vehicle for a further 5k with the same occasional misfire. I then put an expensive brand of cleaner into a full tank and drove up to Glasgow and back (850miles) without a problem.
Then a week ago, after slowing down, what you would describe as Safe mode, but no engine management light, no warning messages. Floor the accelerator and it gradually climbs to 3500 revs, ease on the gas and it shifts gear. It lasts for around 20 secs than woosh power comes in. Still no warnings. Has anyone the faintest idea what is going on? Surely and fault with fuel or sensor should throw up a fault.

[Tannaton]

There is a not very well documented restricted power mode on the D5 where you have good power but it tails off around where 2500 rpm and it won’t rev much above 3000 rpm. There’s no message, no warning light.

The two things that I have come across so far that trigger it is the catalyst or DPF temperature sensors failing and going open circuit, this can happen intermittently.

Should log a fault though....

[taxi driver]

I'm probably totally wrong but the only logical conclusion I have come to is the system does not interpret what's happening as a fault, in other words it thinks everything is performing as the driver intends. In other words something to do with the accelerator pedal input/output.(Accelerator pedal sensor)

[tommyweaves]

Originally Posted by taxi driver

I'm probably totally wrong but the only logical conclusion I have come to is the system does not interpret what's happening as a fault, in other words it thinks everything is performing as the driver intends. In other words something to do with the accelerator pedal input/output.(Accelerator pedal sensor)

I'd agree with that. I had an occasional slight hesitation on my D3. No fault codes, no warning light. Volvo diagnosed the boost sensor was putting out 10x the expected values. Clearly the system didn't see the faulty component, or the component wasn't telling the system it was faulty, for whatever reason. Boost sensior replaced, all good.

[seanc]

Originally Posted by tommyweaves

I'd agree with that. I had an occasional slight hesitation on my D3. No fault codes, no warning light. Volvo diagnosed the boost sensor was putting out 10x the expected values. Clearly the system didn't see the faulty component, or the component wasn't telling the system it was faulty, for whatever reason. Boost sensior replaced, all good.

Unfortunately, no such luck with that fix for me, I just have an occasional 'miss' here or there like the OP. I can't track it down and the car doesn't detect any faults, although it does drive perfectly 85% of the time.

Interested to hear what taxi driver finds out!