[Nickthecook]

I've owned a Euro4 V70 D5 for nearly 4 years and have spent a lot of time investigating the DPF Problems. Primarily, the issue lays with an EGR design problem. Volvo's information regarding this system, is some what ambiguous. The system should have a 2nd MAP Sensor after the Throttle Module, as can be seen on the Euro5 D5. Without this, the ECM can only 'Guess' what's going on based on information taken from other sensors.

The system is based on Ford2003. A High Pressure Loop EGR, that creates a pressure drop on the intake side, by using the throttle plate to restrict boost pressure and adjusting the VGT Vanes to increase exhaust pressure. However, what happens if your EGR is blocked? Or there's a fault with one of the sensors used to calculate this pressure drop? It is possible for a vacuum to be created between the throttle and the cylinders without the ECM having any indication. It might take a 'Perfect Storm' for this to happen, but due to another problem I've identified, the first time the owner has any idea there's a problem, will be the dreaded 'Soot Filter Full'Message. But that's not all, this problem will also prevent a proper regeneration from taking place, here's why.

All of these sensors and modules rely on electrical power and although your voltage readings may be fine, low amperage output from the alternator will struggle to push that voltage past any resistance. The early Euro4's alternator, is controlled by the ECM via the LIN Network. There is a very simple way to tell if there's a problem, but for whatever reason Volvo left it out of the owners handbook. If, when the key is turned to ignition pos2 the 'Check Engine' symbol fails to illuminate, it indicates an ECM Power supply problem (Source VIDA.) With the power steering pump situated directly above the alternator, a few drips of hydraulic fluid onto the carbon brushes is all it takes to significantly reduce output. Early Euro4's were also fitted with a specific type of alternator called an 'Overrunning Alternator Decoupler,' or A.O.D. for short. At the time of production, the pulleys were only available from one firm worldwide, based in North America. They gave the pulleys a surprisingly short life span under optimal conditions, of only 50k miles. My D5 has always been lumpy at idle, something I've always assumed was due to worn engine pads, but I was wrong. The vibration at idle was infact caused by the Alternator pulley.

So far we have the problematic HPL EGR and an alternator that despite charging the battery, is failing in all other areas, now comes the kicker.

The DPF Pressure Sensor is connected to a 5v Reference Circuit (Circuit 2,) as are many other sensors, including the DPF Temp sensor, MAF Temperature Sensor, MAP Sensor and quite a few others. It takes only one of these to develop a fault and it will effect the rest of the sensors on the circuit. However, the alternators drop in output coupled to a 5v ref fault, does seem to over sensitize the DPF Pressure Sensor. With my vehicle, it was the changes made by the HPL EGR on a gear change that caused the 'Soot Filter Full' Messages warning.

Bringing it all together, the setting the ECM puts the car into for regeneration be it with or without the presence of the 'Soot Filter Full,' and reduced power (BTW, 'Limp Mode,' doesn't knock out the Turbo, it reduces fuel flow.) does nothing to improve matters, infact it makes them worse. The DPF Temp Sensor reading will be overstated due to the 5v ref fault and a host of other data required for successful regeneration, will also be skewed for the same reason. Therefore the ECM may think it's reached that critical 600°C, when infact it's under 300°C. Only at that ideal 2,200rpm, will the throttle open enough to prevent the vacuum I mentioned earlier, from sucking oil past the rings, further restricting the DPF (in regen the EGR is fixed at 95% closed.) You may find you get a 'Soot Filter Full,' mesaage, that goes when the engine has been off for 5 minutes or more. This means it is a 'Spike' in pressure, not calculated soot loading, that has caused the message. Spikes are mostly caused by an electrical problem elsewhere. The majority of the data required for the DPF System to function properly, is gathered from sensors on that 5v ref. The same goes for the EGR, which WILL cause genuine DPF Problems.

My 5v ref system was playing up due to a faulty A/C pressure sensor, however it wasn't until I fitted a remanufactured alternator that the ECM finally picked it up. I had MAF Temperatures of -40°C, 7psi boost at idle, 400hpa DPF Pressure at idle and DPF Temperatures of pushing 1,000°c, yet the only fault the ECM could identify.....you got it, the DPF Pressure.

Remanufactured alternator was £140 (less £30 if you return your old one.) P.s. if you need to replace the DPF Pressure Sensor, it has to be a genuine Volvo one (ok, so it's actually a Ford part.) Aftermarket pressure sensors will NOT adapt in range.

BTW, before carrying out the work, I honestly thought the engine was old and ready for scrap at 238,000 miles. It is now quieter and smoother than at any point whilst I've owned it.

Sadly, Volvo only do as VIDA says The first thing they do is read the codes, which in this case is of no use. Yes, replacing the DPF will provide a temporary fix as the flow is so good the faults won't push it into the danger zone......YET.

I can't say this will be the same for all Euro4's. Later models have their alternators connected to the CEM, rather than ECM. But I'd it's using silly amounts of oil, it's down to the Throttle plate causing a vacuum, and that can be happen for other reasons also.