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What Makes a PTC Valve Work?


MVS Forums member Jason Reed posts a fantastic write up on PTC valve electricals and function for turbo cars. PTC = Positive Temperature Coefficient.

I always wondered what was inside the PTC valve and how it worked electrically, so I decided to take apart one of the ones I harvested from the junkyard a few months ago.

I removed the rubber bushing by prying it up and off. Then I used a hacksaw to slice down one side of the main PTC tube. While I was sawing the last bit of the side, when the blade dug into the bottom piece it popped off. The bottom piece is also copper and was soldered onto the copper tube.

What Makes a PTV Valve Work?

Measurements and Teardown on a PTC

On the side of the main copper tube is a small 2mm diameter hole that aligns with the external small vacuum nipple. I was surprised to see how small this hole is, but when I checked the inside diameter of the vacuum nipple, it was also 2mm, so they are matched.

Next I removed the copper wall from the side of the PTC with the electrical connector. I had to pry a bit with a small flat screwdriver and I heard a cracking sound as I pried it apart to reveal the PTC heater element.

The cracking sound was from breaking the solder joints between the copper wall and the contact pin and PTC disc. I measured the resistance from the surface of the disc to the pin 2 in the connector and got ~20 Ohms, which was the resistance between the pins before I took it apart. This indicates that the resistive element in the PTC valve is the disc. The disc is soldered to the copper wall and conducts heat to the copper wall and thus to the gas passing through the PTC tube. It’s interesting that the copper wall is itself part of the electrical circuit.

Measurements and Teardown on a PTC

Tags Oil leak, PCV, Positive Temperature Coefficient, PTC nipple
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2001 V70XC – Brake Pedal Sensor Replacement

Brake Pedal Sensor Replacement


What would be the casualty of a failed brake pedal sensor?
It is showing up in ECM trouble codes.
It is a daily driver in rough winter.
Should I replace it with Volvo part number 9441116 for $92?


The cruise control will cease to work as that part’s major role is to assure cruise will still go off with brake if the brake light switch fails.

Pump brakes until pedal is hard to dump booster vacuum or the or ring on sensor will get sucked inside booster as you pull it out.

2001 V70XC – Brake Pedal Sensor Replacement

Tags 9441116, brake light, brake pedal sensor, codes, cruise control
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1998 S70 Alternator Bearing Change DIY


Atis writes a very detailed Bosch alternator rebuild with great pictures

I had a problem with noisy alternator bearings. The symptom was a high pitched noise which was proportional to the engine rpm, but higher. For me it seemed like some plastic is rubbing on another surface. It occurred only when the engine was cold and the car was sitting for some days. Later it occurred at every cold start.

1998 S70 Alternator bearing change

Tags Alternator, alternator bearings, bosch 0123505014, DIY
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XC90 Advice on Purchase Needed

Volvo XC90

MVS Forums member dosbricks gets great advice on buying a Volvo XC90:

The P80 forum is my hangout, but I’m posting here seeking guidance from those experienced with these SUVs because my wife and I are starting to peruse them as we consider something newer.

This one has very low miles, but accordingly is a bit pricy for an ’04. It is 2.5T but doesn’t say if it is AWD–something we neither want or need in our climate, so FWD is the first criteria. We plan to look at it tomorrow morning just to see if the entrance/egress is good for our senior selves.

As a side note, I still do the upkeep and repair on our 850 and S70–both of which we’ve owned for 16 years, so the 2.4 is very familiar to me. I do realize the newer 2.5T is a more complicated engine than our NAs.

’04 XC90 Advice regarding purchase of this vehicle

Tags Buyer's Guide, XC90 maintenance, XC90 ownership
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Repair Guide: Volvo Door Pop Sound

MVS Forums member bigdaddylee82 rocks the house with a detailed (many photos) guide to repairing the common Volvo door pop sound, which is caused by a weakened/broken check strap.


I drove the car for a week or so with the new door check, and even louder door “pop” when opening & closing, the look on a few coworkers faces that rode with me was pretty priceless…

“You break your door off?”

After further research I decided to attempt the “drill out spot welds, and bolt in place” repair. I picked up some 6 mm bolts & nylock nuts. This “repair” is a bit of a challenge, the door has to come off, easy enough, drilling out the spot welds isn’t that big of a deal, but getting a nut on the inside of the A pillar through that little plug is darn near impossible without being a contortionist. I read every version of the repair I could find on all of the Volvo forums and attempted all posted tips/tricks and a few of my own.


Stupid Question About Door Check Straps

Tags check strap, door, doors
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