Hi, my turbo has seemingly got some issues and just wondered if anyone else has experienced the same problem, I’ve got a 2014 1.5 tdci 75hp it’s done about 90k miles and it’s throwing “engine malfunction service now” at me and a little spanner on the dashboard, it’s done this once or twice before and when I’ve turned it off and back on the problem went however this time it’s persisting and limiting the power every time it’s driven plugged in an obd scanner and got the error P0234 “turbocharger overboost”.

any ideas? 

1 hour ago, Rynham said:

plugged in an obd scanner and got the error P0234 “turbocharger overboost”.

Clear the DTCs and repeat the test a few times to ensure it is a valid DTC. Then I would check out the MAP sensor first, that measures the pressure so failures can be interpreted as turbo failures. Some OBD systems, like FOrscan, can read the MAP pressure.

If you keep getting the same DTC and the MAP sensor is ok, then a fault in the turbo actuator sensor system is the next most likely suspect. Check if it is vacuum operated or electronic. If not obvious from looking at it, then 7zap may help, it looks like vacuum on here:

https://ford.7zap.com/en/car/59/no/15/1551/15391/92848/

If it is vacuum, suspect the solenoid valve first.

Peter, a friend often had that same fault code keep coming up on their focus 1.8tdci but they just lived with it. If it really is overboosting (as opposed to sensor misreading the pressure) what is the possible effect of ignoring it?  Is it just going to be split hose or something more serious?  I’m just interested to further my knowledge

1 hour ago, isetta said:

If it really is overboosting (as opposed to sensor misreading the pressure) what is the possible effect of ignoring it?

In this case the error seems to be limiting the power, or disabling the turbo, so putting up with it may not be a good option!

I suspect my car was over-boosting for at least a year. I kept getting underboost DTCs, which did not limit performance in any noticeable way. It turned out to be the little pipe to the pressure (MAP) sensor, so the sensor was reading low, and this would make the ECU boost up the turbo to try to get the right reading, at least until the error came on. So I suspect it was running with too much boost most of the time until I finally spotted the quite obvious problem (I think I had discounted it, assuming I had checked it, but had somehow just not seen it! Like looking in all nooks and crannies for lost keys, only to find them on the desk just inches from their normal location! )

I doubt if a while running with excess boost does any lasting harm, it will waste some fuel, less efficient running, but the maximum pressure is limited by the design of the turbo.

The main problem with prolonged overboost is over-speeding the turbine shaft.  That can overheat the bearings leading to wear/play which could eventually snap the shaft.

As you say, there's unlikely to be any engine damage as the boost pipes should be the weakest part of the system and blow first.  But even after pipes have blown, that doesn't reduce the turbo shaft speed.