Two Sensors Die at Once? 98 v70 T5

[WagonLagan]

Unplugging it can set a code, but basically will do nothing else unless you are driving from the high rockies to the Gulf of Mexico in one (fast-moving) day. I've done it before when trying to cure stray baro code - it didn't affect driving at all.

In that case, I'll unplug it and see if that resolves anything. If not, I'll smoke it on Friday.

I think you missed a key point - a 98 V70 runs on motronic (m4.4) not fenix engine management, so check again because likely there is no shared violet wire.

Does ^this^ mean that unplugging the MAP sensor is irrelevent?

[erikv11]

Yes that is the whole point: the name MAP sensor is misleading and actually not even used here, it is actually a "BAP" sensor (see https://www.fcpeuro.com/products/volvo- ... 0261230018). The sensor on your car measures outside air (Barometric) pressure, not Manifold (the M in MAP) pressure.

However I do not know if there is a shared wire with the TPS, I defer to mrbrian or someone else.

[abscate]

It's always hard for me to convince myself a little rubber hose can cause all this,

You can search these pages to find a *few* examples of this...

[sleddriver]

Could be the cable to the fuse box. It's happened before, it might be happening again.
The atmospheric sensor on a 98 is right in front of the fill hole for the windshield washer fluid tank. It does next to nothing on a 98.
Unplug it and leave it unplugged and see if the car acts up.

Wouldn't unplugging it cause the same issues as if it was malfunctioning? I did clean it to no benefit.
In other news: I built a smoker, and am waiting for the caulk to dry to give it a try.

Unfortunately the baro-sensor is a damn expensive part. Mine went Tango Uniform. I ignored the code for a long time before buying a new one. Do your self a favor and go pull one from a junk yard FIRST!

You can't always clean them.

[sleddriver]

It's always hard for me to convince myself a little rubber hose can cause all this

Oh yea it can....

Turbo motors are very, very sensitive to vacuum leaks. Any unmetered air entering the system causes problems. Further, in boost, you lose pressure. Thus any leak is a two-edged sword.

By now, ALL vacuum hoses, elbows, intake vac tree "caps" & gasket, and both B&W check valves should all be replaced. These cars are close to 20yrs old now!!

[WagonLagan]

Unplugging the MAP baro sensor didn't help.

I may have found the issue.

About 2 years ago I had replaced the PCV system, and one of the vacuum hoses onto the... okay I don't know what it's called. It's on the vacuum tube tree that is down the tube from the MAF.

Anyway, I jerry-rigged the vacuum hose there because I had limited options, then promptly forgot that I should go back and properly attach it!

The smoke test (thanks for that suggestion!) led me to it, and I noticed that particular vacuum tube was completely off the tree. Whelp. I'm fixing the tube and reattaching it. We'll see if that fixes it. I suspect it will.

I'll update after a couple days of driving.;;

[erikv11]

It's not a MAP it's a baro sensor! Glad you seem too be tracking it down.

[WagonLagan]

Whelp... That didn't work. If anything it seems to have gotten worse, lol.

https://vid.me/gMiUm

And, interestingly... the CEL comes on, but there's no codes according to my OBDScanner.

During the smoke test, I couldn't see any areas of significant smoke leakage, apart from the one that had fallen off. However, given the fact that it got WORSE after replacing that vacuum hose, I find it unlikely that a damaged vacuum hose is the root cause here.

If it helps anyone diagnose, before this happened, I did have rare, occasional stutter for months, but never, ever this bad. Just an occasional dip, not even once a day. I just chalked it up to 250k miles.

I may have to take this to my Indie... I really don't want to shell out a couple hundred for what might be a simple fix, but I just don't have time to pick the car apart right now. Sigh.

Before I do that, any thoughts on things I could try? Anything that isn't a huge time investment, I'll go for.

My first course of action is to find a replacement Baro sensor. It sounds like that could be causing these issues from what I've read above?

Could electrical issues with the wires to the TPS cause this? If I have to take it to the Indie, I'd at least like to give them a place to start looking.

[jblackburn]

I seriously doubt the baro sensor has ANYTHING to do with it. That's something you pick up just to make the CEL go away once the car's running properly.

It's idling rather like my car did when the MAF was giving off weird readings, though. I kinda doubt the TPS is doing it either. On a 98, it should idle smoothly even with a bad TPS; on the other hand, shift quality will feel like a dump truck.

I think you need a live scanner hooked up to see what sensors are reading what.

As a test (it will throw a code), disconnect the MAF plug with the engine off and see if idle stabilizes.

[mrbrian200]

Yes I did miss something big. Because I saw "MAP", assumed it this NA and missed the important "T5" designation in the thread title. I thought Volvo referred to these on the turbo models as an altitude and/or boost pressure sensor (because it's positioned before the throttle plate on the intake it's not measuring MAP)
On '98 motronic the TPS shares a ground circuit with the acceleration sensor, camshaft position sensor, and ambient air temperature sensor. All other wires to these specific sensors are dedicated. Purely conjecture: Some of them may still share a common supply voltage through a voltage regulator inside the ECU with the junction being inside the ECU board traces or a solder joint.

I can't seem to figure out on the diagram which component is the altitude/MAP sensor. The older diagrams leave a lot to be desired (such as a component list that lists everything-named). That list is somewhere else not within the wiring diagram section I'm looking at.

I still think it's a sensor/wiring/ECU problem. He needs to backprobe various circuits while it's acting up and/or examine live data on an OBD tool. My basis being the persistent DTC for the throttle position sensor: it doesn't matter how good or bad it's running, that DTC should not pop up with a known good sensor unless the ECU compares expected MAF air flow to the throttle plate position and it's a malfunction of the MAF throwing the works off. Just for S&G have you tried running it with the MAF disconnected?