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Help, Focus st boost issues!!!

4988 Views 20 Replies 4 Participants Last post by  Haranv_st
I just bought a 2016 ford focus st. I am already having issues with it. It seems that my ECU can’t match the amount of boost i’m pushing. Very weird noise when I hit boost and my BOV isn’t going off correctly. The car when you let off the gas throws you forward kind of. I am running very rich and i don’t know what to do. The engine code was something about “Turbo boost sensor” “Circuit A” I already replaced both MAP sensors and all the plugs and coils. Im not sure what else i can do and i don’t want to take it to a dealership, if anyone can help please help.
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What was the last thing you (or someone else) did to the vehicle?

What was the exact DTC?
Well, strange noise under boost could be either a boost or exhaust leak.

The DTC P0238 Turbocharger Boost Sensor A Circuit High means that the PCM sees higher than reference voltage. The sensor in question houses two separate sensors. The CACT (charge air cooler sensor) measures the air temperature post intercooler and the TCBP (turbocharger boost pressure) measures the amount of pressure after the intercooler but before the throttle body.

The sensor has 4 wires. Pin1 is the SIGRTN (ground), Pin 2 is the CACT return signal to the PCM, Pin 3 is the VREF (5 VDC +), Pin 4 is the TCBP return signal to the PCM and is the offending wire.

The "high" portion on the DTC means that more than the expected voltage is being sent to the PCM. A quick test would be to disconnect the sensor and see if then code changes to "open" versus "high". *note it is important to remember that you will also see a code for the CACT because of the disconnected plug.


If the code remains "high" after the sensor is disconnected you could potentially have an issue with the PCM.

You said that:
The person who owned it before me i believe was running a tune but i don’t have that access port but i ordered one that might be the issue but i’m not sure
Did you mean that he reverted the vehicle back to stock configuration and unmarried his AP from it? Or that the tune is currently installed and he kept the AP? Sorry just seeking clarification on that one.

You need to check the wiring on the vehicle for damage. As strange as it sounds double check the bank 1 O2 sensor wiring as I have seen the wiring become damaged on aftermarket down pipes and cause ass sorts of strange issues with the PCM.

Stay Safe

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Cold engine (minimum 6 hours)
Set the AP to monitor BARO, MAP, TIP Actual
This test looks to see if the three related pressure sensors and in agreement or if one has failed.

Do not set the vehicle KOEO (key on engine off) * if you start the engine you will have to wait the 6 hours again.

They should be very close to one another, but note that they will not be exactly the same.

It's likely that your MAP (manifold absolute pressure) sensor has failed. It is located on the intake manifold itself. People swear the you can clean them but this issue will return.

The TMAP is mounted on the passenger side end tank of the intercooler and is responsible for reading the pressure & charge temperatures before the throttle.

The BARO reads the barometric pressure and it physically integrated into the PCM (powertrain control module) located in the drivers side fender well.

@Haranv_st Start with the test above and let us know.

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The P018C is a low pressure fuel pump related code however this may also be triggered by the MAP sensor as the PCM cannot accurately calculate fueling needs.

Have you ever changed your purge valve?
thanks for the reply! I will go ahead& try that tomorrow also I did replaced the map sensor located on the intake manifold with part #AG91-9F479-AC just today! But like I said before whenever I gaved It gas It would struggle and would hear like misfires..
If the TMAP has failed then it can definitely cause those symptoms. So far you've replaced 1 of the only two field serviceable sensors on the vehicle.

I did change the purge valve about 2 years ago
They don't last as long as you may think they do.
So i got this.. seems like the TIP Actual abs is bad right ???? View attachment 405878
46.81 - 14.65 = 32.16 PSI

Pretty sure you've found your problem... :ROFLMAO:

Check the plug and the surrounding wires for damage. You can disconnect the sensor connector and check to see if the TIP drops to nothing. This will help to determine if your dealing with a failed TMAP or wiring issue.

Sorry ai couldn't have gotten to you before you swapped out your map sensor.
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