XC70 with hesitation and codes

slc10844 · Post by **slc10844** » 08 Feb 2009, 12:09

My wife has a 2002 XC70 with 64K miles. Vehicle has been throwing P0236 & P0237 codes which have to do with the turbo boost sensor. I have already checked hoses and wiring. Everything appears to be OK. Freeze frame show the codes always set before the engine is up to operating temperature. I cleared the codes yersterday and as soon as the car was started today the codes were back. I drove the car and noticed, especially when the engine is cold, a hesitation when initially pressing the accelerator. It will sometimes hesitate when the engine is warm but it is much less noticable. The hesitation is like a carburated vehicle with a bad accelerator pump. Full throttle it runs great. Turbo kicks in and will run up to 6K with no problem. Any suggestions? She only uses premium fuel and the oil is changed ever 5-6K miles with Mobil 1. I'm thinking of taking it to the dealer but if it is something simple would rather fix it myself.

Post by **MadeInJapan** » 08 Feb 2009, 14:22

Welcome to MVS. Certainly your turbo control valve could be the culprit...make sure everything is connected to it...it resides on the side of your air cleaner box and has three hoses running to it- they are marked yellow, blue and red. The red one goes to the bottom of your turbo...the blue one runs to your blow-off valve and the yellow one runs to right under your accordion intake hose (right past your MAF)...often the yellow one gets disconnected. Otherwise, your symptoms could be the early signs of a failing MAF sensor. How many miles are on your XC?

slc10844 · Post by **slc10844** » 08 Feb 2009, 15:12

The car has 64K miles on it. I checked all of the hoses and they are in good condition. No cracks, soft and pliable. I'll have to trace them to where the connect in the back of the engine tomorrow. Any chance it might have something to do with the electronic throttle? Will the turbo control valve cause the hesitation coming off idle? The strange thing is when I check the freeze frame on the scanner it is showing zero vehicle speed and zero engine speed. I don't have a Volvo specific specific scanner and have to resort to using a Euro Generic OBD II program.

Post by **MadeInJapan** » 08 Feb 2009, 16:58

Zero speed at start could be a speed sensor going bad (this is typically the rear cam position sensor on older cars- may be the same on your, I don't know). It will signal to the ECU for the right air/fuel mixture too so that might be the cause of your hesitation. On earlier Volvo's ('98-'00), if you look straight down past your upper engine torque rode, you'll see a silver cover over the cam...this is it. I'm not sure if yours had it or not. Your XC, being a '02, it would not have the typical ETM issue that '99-'01 (and some '02 C70's and S80's) had.

slc10844 · Post by **slc10844** » 10 Feb 2009, 13:26

I did some more checking yesterday. Looked really hard at the vacuum hoses and they are all in good shape. Checked for any loose grounds, at least what I could see, and they are tight. Is it possible the electronic accelerator control could be bad? When pushing on the accelerator pedal just off of idle it is like it looses connection for a split second and catches right away. It does this mostly when cold. Don't know what relationship what it would have to the codes but I think one problem is connected to the other.

Post by **MadeInJapan** » 10 Feb 2009, 15:39

Sorry, but I have no idea- maybe others will chime in.

I'm still thinking turbo boost controller (turbo control valve- TCV). I changed ours out in our '04 V70 with IPD's heavy duty version- nothing was wrong with the one that came out. If you want, I could send you the old one and you can try it and see if it works. If it eliminates your problem, then you can buy it from me (I'll be fair with price). If it doesn't work, you just send it back and pay me for my portion of the shipping. If this seems like a decent idea to you, then let me know here or PM me. My email is in my profile or you can email me from within MVS.
Regards,
MIJ

slc10844 · Post by **slc10844** » 11 Feb 2009, 14:46

Would the TCV cause a loss of fuel mileage? Wife said she lost about 3mpg. How can you check to see if the turbo is spinning free? Her 95 V70 the turbo was quite pronounced. We bought this 02 new and its always been hard for me to tell if there is turbo whine or just engine noise.

Post by **MadeInJapan** » 11 Feb 2009, 20:15

If you're talking about the turbo lag (kicking in late) then this is fairly normal especially on a cold engine- the cure would be to let the engine warm up. That said, I'm confused about your statement of getting a new 02 sensor. As far as I can tell, this is the first reference to an 02 sensor (unless I missed something). You're losing 3 or so mpg...this could be just winter gas with alcohol added to the gas or it could be an 02 sensor going bad...I'm not sure what happens when an TCV is going bad...I just changed our out (both FWD cars) to have a smoother boost with the turbo...the turbo whine is from right in front of the driver's side of the car- if it's coming from the other side, you've got something else going on.

slc10844 · Post by **slc10844** » 13 Feb 2009, 15:26

I'm happy to say it is fixed. After much searching for a cause for the two codes, P0236-turbo sensor and p0237-turbos circuit "A" low, I had several suggestions but no cure. I checked wiring, connectors, hoses and grounds. A Volvo tech said he had a couple cracked turbo housings, which was also checked. Everything seemed to be OK. A vacuum leak was one of the first things everyone kept saying was the problem. I sprayed induction cleaner around the engine compartment with the engine running searching for a vacuum leak. Engine speed never changed. Its the wife's car and all I kept hearing was she was affraid it was going to leave her stranded. Since both codes had turbo sensor specified as the problem I decided to get one. Of course the dealer calls it a MAP sensor, which was part of the problem. Not the same terminology but they are both sensors. Installed the sensor, started the engine, tried to duplicate the hesitation and it wasn't there. Took it out on the road, no hesitation and accelerated smooth with plenty of power. Could even hear the turbo whistle at times. Not that I drive the car that much, its the wife's car, but don't remember it doing that before. The clincher is the CEL light went out on its own. Didn't need a scanner to turn the light off. Sometimes you can't see the forest for the trees. Sorry if the post is a little long, but I hope it helps someone else with the same problem.

Post by **MadeInJapan** » 13 Feb 2009, 16:55

Glad your problem has been solved!
I'm curious about that MAP sensor...do you have a part number, a better description or a picture? I went round and round with a buddy here in K-ville a few weeks ago about one for a '98 S70 and it ended up being an "altitude" sensor, but was referred to by some shops and even in some Volvo documentation as a MAP...go figure.