Engine: D5: 135F MAF sensor signal intermittent EML, poor cold start

[Ruffgeezer]

For the last few months, there has been a reoccurring fault with our 2007 (ph2) V70 D5 (silver engine cover)

It would:
1) Start then cut out straight away when cold unless throttle applied.
2) Intermittent engine service message, fault code points to the MAF sensor 135f Faulty Signal.

It is a low mileage (50k) automatic, and since buying it earlier in the year, ive had I've had the egr apart as it was clogged, stripped the inlet off and put a new set of swirl flaps in as they were worn, these improved drivability but the intermittentfault was becoming more regular.
All the previous work needed doing as there was considerable soot build up, well, everywhere!

Now it's very easy to just fire new parts based on the fault codes, but with the data logger on, the readings I was getting from the MAF always seemed to be pretty reasonable, and sensors when they are duff tend to stay duff.

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It is always worth looking at the other related data when you've the opportunity, as I did, to see if anything else seems amiss. In my car's case, the Inlet Air Temperature sensor was reading 105 degrees C, which didn't seem probable in early spring! It is part of the boost pressure sensor also.

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Even just hanging the new sensor on the wires gave a far more sensible reading of 16deg, so I'm quietly hopeful that I've the problem solved. I suspect that because the ECU thought the air was a lot hotter than it was, it was throwing all the other readings out.

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Last pic is the location of the sensor, just behind the intercooler.

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[dikidera]

On my S60 2.4 petrol, the Intake Air temperature sensor was integrated in the MAF. Are you sure yours isn't the same type? If so, then it is faulty or you might be able to clean it up with some MAF cleaner and maybe just maybe revive it.

In 40c(yes celsius) heat, on my black S40 NA, I would seldom see 75c temps.

I mean all your conclusions point to the MAF, not sure how it wouldn't be the MAF. So I think this time, you can trust the scanner and it's codes.

[Ruffgeezer]

You've got to trust the data, the inlet temperature measured at that sensor thought when the car was cold that the inlet temperature was 85 °C.

It tells the ECU this, and the ecu will adjust the fuelling to suit what it thinks is the correct temperature. It clearly wasn't 85°C on my damp driveway in Lincolnshire at 8pm.

To prove the bad reading was coming from that particular sensor, I left the data logger on and unplugged the boost/ air pressure sensor (as pictured above) on the back of the intercooler. This then produced the default reading of -40°C.

As I had previously read the fault codes and the data before, I was already suspicious of the high inlet air temperature reading, hence ordering the replacement sensor.

I suspect the false code for the MAF was because (a) The ecu was told the air was way warmer then it was, and therefore the anticipated air density was way off, and (b) because the MAF was expecting less air than what it was actually getting, it threw in a code for misreading.

As I said previously, you have to trust the data, not the fault codes. The ECU will treat all readings as fact, it is up to the data to prove or disprove it.

[dikidera]

Could've fooled me, but you see, my MAF has an integrated intake air temperature sensor. So if I had a MAF code, I'd trust it.

If your boost sensor had the IAT integrated, then that was the faulty part, yes.

To me it seems like the ECU prioritized the MAP sensor over the MAF and trusted the MAP's data and thus flagged the MAF. Why? Well we can only guess.

Volvo use the pass through turbo setup. Air goes via Air filter box->MAF->Turbo->Intercooler->Intake manifold. Makes sense that it would flag it, since it is it's primary source of information.

[Ruffgeezer]

I cannot comment on your specific MAF sensor, or indeed as to if the one on mine has an inbuilt air temperature sensor.

I can see your reasoning, but the data is taken as a whole rather than in sequence from the MAF onwards.
I am certain there will be some formula that calculates the volume of air at certain temperatures. Because the temperature being read was so far off of the actual temperature. ( Google gives a figure of 1% less air density per 3°C increase in temperature) so with the IAT resding 9 times higher than the actual temperature, the ECU thinks that the air density is going to be far far lower than it actually was. When correlating this data with what it reads at the MAF, all it knows is the figure there is implausible, because it has treated the temperature reading as fact.

[blackpxyton]

I had similar issue - getting this MAF error code but no issue with cold start. But also noticed temperature differences. Changed IAT sensor (same code as yours) and it started to show correct temperature (thanks for this guidance). Air mass changed from 50kg/h to 25kg/h, desired air mass changed from ~500mg/s to ~250mg/s (same as air mass/stroke). Do you have same numbers for air mass?

[SteveSarre]

Hi all,


I have recently replaced the boost pressure sensor on my 2006 2.4D E4 and found that that unit does both temperature and pressure

Google
"0 261 230 295" "Bosch" "temperature" "pressure"

On that same car I believe the MAF 30677999 does not include a temperature sensor.

Hope that helps,
Steve