P0234/p0236

[sjonnie]

Check engine light came on when I started the car after work today, never seen it on before, definitely wasn't on when I parked the car. Checked for messages on the DIM but nothing, ran the diagnostics by pressing the fog light buttons but still nothing. Drove home, seemed fine although didn't want to try WOT. Plugged in my OBD2 reader when I got home and got:

P0234/ECM-6805 = Turbocharger (TC) control valve, boost pressure fault. Pressure too high
P0236/ECM-170F = Atmospheric pressure sensor / boost pressure sensor range check. Faulty signal. Intermittent fault

Reset the codes and restarted the engine, no engine light. Drove around the neighborhood, again nothing. So I'm guessing faulty signal from MAP sensor. Should I clean it, replace it or do nothing and wait to see if it pops up again. Or could it be something else?

[Aviator]

Sounds like the turbo wastegate isn't opening when it should, causing higher than normal boost pressure which would cause higher than normal pressure in the intake manifold which would then give you the second code. Perhaps the boost control valve is shot.

Dave.

[sjonnie]

Perhaps the boost control valve is shot.

Hmmm, I hear it clicking on and off, any other way to test if it's functioning correctly? Also sometimes during idle the engine shudders like it wants to stall out and this seems to be associated with rapid boost control valve clicking...

[JRL]

New BCV about 40 bucks and they DO fail

[justthefacts]

When I'm stopped and idling (in Drive), after about 45 seconds (although I've never timed it exactly), my '04 engine also gives a quick one-second shutter as if it might stall. But it doesn't, and after that, it's back to normal. Maybe plugs? I'm not experiencing your clicking noise or trouble codes though, so I can't offer any advice.

[sjonnie]

After resetting the codes the car now shows up new ones immediately but the check engine light doesn't come on until you switch off and restart, so I guess it's a permanent fault. The codes now are

P0236/ECM-170F Atmospheric pressure sensor / boost pressure sensor range checkFaulty signal. Permanent fault
P0237/ECM-1600 Boost pressure sensor. Signal too low. Permanent fault

So sounds like it is the MAP.

[riceboyler]

After resetting the codes the car now shows up new ones immediately but the check engine light doesn't come on until you switch off and restart, so I guess it's a permanent fault. The codes now are

P0236/ECM-170F Atmospheric pressure sensor / boost pressure sensor range checkFaulty signal. Permanent fault
P0237/ECM-1600 Boost pressure sensor. Signal too low. Permanent fault

So sounds like it is the MAP.

New member here. I have my car at the shop today for the same codes. I've got a 2002 XC70 with 110K on it and I'm being told $295 to replace the boost sensor. I'm fairly mechanical, and would prefer to fix it myself. Where is the sensor located, and on scale of 1 to 10 (10 being a full drivetrain swap), how difficult is it to replace?

[sjonnie]

Sounds about right. Dealer price for the boost sensor is $99.61 +tax, time to open hood and replace boost sensor, 5 mins, time to plug in diagnostic computer and run VIDA to reset codes and test function, 5mins. As far as I can tell, Volvo dealers charge $300/hr for labor but judging by the $295 quote you got they are adding a $140 surcharge for the great service and wonderful feeling you get by being a Volvo owner and using an authorized dealer

You could order the part here for $71 and fit it yourself but then you wouldn't get that wonderful feeling you can only get by blowing a huge wad of cash for nothing.

[Aviator]

So sounds like it is the MAP.

I would have to disagree with your logic on this one; you are getting the MAP sensor code as a result of the boost control valve problem. It's more likely that the BCV is shot than the MAP sensor.

Dave.

[sjonnie]

According to VADIS, the EMS compares the signal from the MAP sensor with the EMS atmospheric pressure sensor at start up before there is any boost, if the two signals are found to be different P0236 is immediately generated. I am getting P0236 as soon as I switch on the ignition after clearing the code. Again, according to VADIS with just the ignition on, i.e. no boost, the MAP should be returning 1.96V, mine is returning 0.3V, which will then generate code P0237. Pretty sure it is the MAP.