No AWD...again.

[cheapo]

Last fall we noticed our rear wheels were not engaging. Our mechanic diagnosed it as a faulty differential oil temperature/pressure sensor. He cleared the error code and ordered the part. In the week that passed before we had the part installed, the AWD worked without issue.

After the part was replaced, we enjoyed AWD for the rest of the winter.

Here we are, about one year later, and the AWD is out again. I don't know for sure when it failed, as I don't usually notice it's gone until I need it. That said, a few weeks ago, we had some rain and I decided to test the AWD. From a stop, I goosed the gas pedal. The car accelerated with no wheel spin.

Today, we're having LOTS of rain and a bit of slush and, sure enough, no AWD.

If it is the same sensor that needs replacing, why would that be the case? What is it that can wear out an oil temperature/pressure sensor in one year? Could the very wet weather be messing up the sensor or DEM?

All advice appreciated.

[cheapo]

I have a theory:
The pressure/temp sensor is the culprit again, but it isn't toast, it just needs cleaning...it needs cleaning because the lubricant in the Haldex is old and funky.

1. Pump out and refill Haldex.
2. Clean temp/pressure sensor (and reset error code).
3. Profit.

Opinions?

[Xilikon]

If the mechanic replaced the sensor without flushing and refilling the Haldex module and cleaning the filter, this might explain why.

I saw around here a link a user posted about the Haldex oil fill plug and the filter location. One of the pics have shown the filter was full of sticky gooed crud.

EDIT : Found the post -> http://www.volvoxc.com/forums/showpo...92&postcount=5

[JRL]

Volvo parts and labor are now warranted for 2 years
However if you used an independent, I'm not so sure.
Probably/possibly the part, not the labor

[cheapo]

We took the car in on Monday and I asked the mechanic to pump out and refill the Haldex oil, clean the pump and to replace the filter. I picked up the oil and filter at the dealership and delivered them to my mechanic.

At the end of the day, I picked up the car and my mechanic told me:

1. There were no codes, before or after the work was done.
2. The oil was replaced and the sensor and pump were cleaned.
3. They drove the car and confirmed the AWD was working.

I walked out to get the car and noticed the filter was sitting, still in its package, in the cargo area. They forgot to replace it. (Ugh! He'll do it free of charge next time the car is in, he says.)

The car has been back from the shop for 3 days and the AWD is gone again!

What is most likely wrong?

Could it be the sensor again? The DEM?

I don't think it's the bevel gear collar as we've had no grinding noises ever.

[JRL]

I don't think it's the bevel gear collar as we've had no grinding noises ever.

If the collar is worn but not broken, it will not make any noises but if it has slipped out a bit it's not grabbing the gears.

My mechanic has told me that in this case you need to apply the gas carefully using little torque and it may work
(That's if your issue is the collar)