Engine: 2.5: What happens if MAF fails?

[ocean238]

How do you know if you MAF fails? ie, what differences does it make to the way the car runs?

Thanks

[saturnuranus]

I left mine unplugged after doing some work under the hood once and the car wouldn't start. Not sure what happens if it packs up on the move.

[ocean238]

right, that's strange, mine has been unplugged for a while, but nothing has changed

[1999s70]

I've had mine fail twice. The purpose of the MAF is to make fine adjustments to the position of the throttle plate, taking into account temperature and humidity of the air.

When the MAF starts to fail, the car will seem like it's missed a beat when you're running at highway speeds, it will resist you when you try to accelerate, or will try to stall out when you rapid slow down, like for an exit ramp. Two characteristics distinguish MAF failure from a throttle (I've had three of those fail, too) - a failing MAF does not show itself when you're sitting at idle, and, while driving, forcing a downshift to increase engine speed will have no effect. The symptoms will get progressively worse and more common, and they'll be worse on very warm or very humid days - when the MAF would be making the most adjustments. It's also common to NOT have an error code stored in the car's computer - though sometimes a Volvo VADIS code is stored, when there's nothing that an OBD reader would pick up.

I've had my two MAF replacements very shortly after having the throttle replaced (I have the "magic throttle" of S70 fame) - and I undestand from my Volvo Techs that this is not unusual - so, as a precaution, I'm just going to automatically replace my MAF whenever the throttle gets changed.

If you're sure that the problem is the MAF, I have posted elsewhere on this forum detailed instructions how to replace it yourself - I replaced mine in under 5 minutes - it requires nothing more than a 10 mm socket and a screwdriver - you can save yourself lots of money by buying one yourself (about $180 in the US, versus $250+ at Volvo) and replacing it without paying Volvo for an hour's labor (another $125) for a 5 minutes job.

Hope this helps.

[s60ben]

Originally Posted by ocean238

right, that's strange, mine has been unplugged for a while, but nothing has changed

Apart from your mpg will have gone down into the pits very probably... without a MAF signal the ECU will fall into it's protection/reduced performance mode.

Maf Failure/missing =

Substitute ECU value's
-initial boost pressure
-rear heated oxygen sensor (HO2S) control shut off
-misfire diagnosis shut off

Fault symptom[s]
-poor performance

[BillB]

Originally Posted by ocean238

How do you know if you MAF fails? ie, what differences does it make to the way the car runs?

Thanks

I have a Tdi V70 and when the MAF was failing it had a MAJOR effect on performance e.g. it wouldn't climb hills and wouldn't accelerate very quickly. A new MAF had a DRAMATIC effect - different car. I imagine a petrol engine would have similar effects. The MAF is a major component in setting air/fuel mixture andd the engine ECU will go to a default setting in the absence of a MAF signal. Have the codes read - that will confirm MAF failure. An intermittent CEL light would be a sign. Regards.

[liuleichan]

Originally Posted by ocean238

How do you know if you MAF fails? ie, what differences does it make to the way the car runs?

Thanks

Your details say 2.5 10v, so your engine doesn't have a MAF sensor. It has an air temperature sensor, in the airbox main ducting, that if you unplug, will likely do nothing, in the short term, but may raise a fault code if you leave it unplugged.

Your engine will have a MAP sensor, that's on the bulkhead, just above the radiator, with a vacuum, white pipe going to it. If you unplug that, your engine will die (not permanently, though!).

[Timbo_1975]

Just what he said.. (re the MAP sensor on the Fenix system- 10valvers)

The air temp sensor (where the MAF otherwise would be) if unplugged- the ECU will assume a default value which in this instance is 20deg c.

Tim.
.

[Clan]

Originally Posted by BillB

I have a Tdi V70 and when the MAF was failing it had a MAJOR effect on performance e.g. it wouldn't climb hills and wouldn't accelerate very quickly. A new MAF had a DRAMATIC effect - different car. I imagine a petrol engine would have similar effects. The MAF is a major component in setting air/fuel mixture andd the engine ECU will go to a default setting in the absence of a MAF signal. Have the codes read - that will confirm MAF failure. An intermittent CEL light would be a sign. Regards.

The diesel suffers a lot more when the Mass Airflow Meter fails because it doesnt have any feedback or adaption from the exhaust gas like a petrol Lambda sensor system ....

[ocean238]

right, so there is no MAF, ok, because i was getting worried that everyone is saying how important it is, i left it unplugged to other day by accident, and the car is just as before.

Altho it's beginning to idle at 700-750 rpm instead of around 900..

What are the differences between MAF and MAP?