01 XC70 with low power/low boost
 

i am an ex BMW tech, but i am really at a loss on this. 01 XC70, 99k miles, i've owned for about 2 years 87k miles. seems to have been getting weaker/low on power. no CEL. seems somewhat intermittent. sometimes car feels ok, other times takes about 1" of pedal travel to get any power/move the car. have noticed it is really lacking lately, downshifting on hills, just working too hard without much grunt. researched this site, last week i replaced the turbo control solenoid, no change. i spoke to an area volvo shop, they suggested that i bring it in to check engine/trans codes. i have OBDII scanner, checked and was surprised to find P1238. i reset, and the car is definetly better, but still not right. i dug out an old stand alone boost gauge and hooked up today. this is what i found. about 95% of the time the engine is in VACUUM. at idle i have about 20hg, at highway speeds coasting have about 30hg. drive the car moderately, up hills with medium throttle, etc. never get to zero - if i give it about 3/4 throttle i get a solid 5psi of boost. i say solid because it apears that it is being regulated at 5psi, not floating/jumping around. again, even at 5psi the car really feels like its working hard, certainly not running right. there is nothing obvious, all vac lines seem ok, turbo cold piping hoses and couplers look fine. untill i put the boost gauge on today i was thinking possibly my cat was becoming restrictive, but i can't see exhaust backpressure resulting is a solid 5psi of boost across the rev band. any idea would be greatly appreciated. additionally, other than the low power, the car drives smooth. on the turbo compressor housing there is a triangular device/possibly some kind of diaphram, i am not sure what this does. i am not referring to the wastegate actuator, this seems to be part of the compressor housing casting. MANY, MANY thanks. todd

I would make sure the turbo is working properly. (BTW check your PM's)

Similar problem as you state....Found this on another site....

That code converts to volvo code ECM-6806 and the code description as described in the volvo service manual:


284: ECM-6806 Turbocharger (TC) control system flow fault. Flow too high/low. Permanent/Intermittent fault, B6284T

Diagnostic trouble code (DTC) information

Condition
If engine speed (RPM) is above 3500 rpm and the engine is operating at a high load, the control signal to the turbocharger (TC) control valve is at maximum and the boost pressure (from boost pressure sensor) is lower than a designated value (approximately 20 kPa (2.90 psi) under normal boost pressure - signal too low).
If the air mass (from mass air flow (MAF) sensor) is higher than a desired value (signal too high) it is interpreted as a fault and diagnostic trouble code (DTC) ECM-6806 is stored.

Substitute value
reduced boost pressure

Possible source
Signal too high:
-air leakage after turbocharger (TC)
Signal too low:
-hoses between turbocharger (TC) and turbocharger (TC) control valve respectively turbocharger (TC) control valve and pressure servo are loose or are blocked/damaged
-faulty turbocharger (TC) control valve
-faulty boost pressure control (BPC) valve pressure servo
-sticking boost pressure control (BPC) valve



I would say that considering you just replaced coils and all the tubes were off on top of the engine, one of them may be loose, leaking or damaged. Good luck fault-tracing.

2001 v70xc, CEL on, codes:
p0235 ->Turbo/Super Charger Boost Sensor A Circuit
and
p0236-> Turbo/Super Charger Boost Sensor A Circuit Range/Performance

It does not perform any worse than before so it doesnt make much sense:confused:. Both these codes are related to sensor A and by looking at more codes I realized that there is a sensor B so how do I know which one I have to replace (if it the sensor at all)? Tech where are they located? eeuroparts is not selling them and I coudnt find 'em at fcp groton either.

thanks!

The map sensor is located in the plastic pipe going to the throttle body.
The part # should be 9125462.

ok thanks!
MAP stands for manifold absolute pressure right? Does turbo have a boost sensor on it's own, or 2 of them maybe?? Reason I am asking is I noticed that this same sensor can be used on bunch of other volvo models, some of them non-turbo's. How is that possible? Sorry to be pain in the neck, you have always been very helpfull and right on advices, where am i getting this wrong?:)

Yes they use is on the S70,S40 and other models. They also call it a pressure sensor and a few other names as well.

On your car next to the map sensor is a air intake temp sensor.

Ok, thanks tech:)
I located sensor, it's easy to replace. Before I go ahead and order it, maybe I should check for other possibilities that can trigger this code(s)? My car drives just fine, i see no problems with pick-up or anything. Any advices?

If you can I would just replace the sensor.

ok, i will do that tomorrow and keep you posted...i take it you replace a lot of these sensor, you seem to be sure that is the problem

I have done a ton of them on the S40's not all that many in the V70's but they are the same sensor as the S40's.

replaced it, cel is still off but i only drove it for few miles...going away for few days, will see what happens when i come back and do more driving. thanks tech!

Any updates?