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Gallagher99, Senior Vehicle Technician
Category: Ford
Satisfied Customers: 3325
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Hi We have replaced a turbo and actuator on a Ford S Max 1.8tdci

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We have replaced a turbo and actuator on a Ford S Max 1.8tdci engine and after bout 20 miles the MIL light comes on and the code (read from Autel Maxys) is
P0299:08-E8 Turbo Underboost.
Any one had this code before - Customer not happy at my premises this am !!
Hi there ,good afternoon to you

Ok this is a turbo underboost code which can be caused by several things but most commonly a small split in the intercooler hose which attaches to the inlet manifold (drivers side rear if the engine bay )
This would be my first check as these are quite prone for tearing/splitting on the underside of this hose
And causing an underboost condition

Kind Regards XXXXX XXXXX

Hi there how did you get on with this issue


Customer: replied 3 years ago.

Hi Brian


No joy I'm afraid, pipework all good - we think the problem is coming

from the exhaust side and was hoping the end of the fault code 08:E8

would trigger a response.




Hi there ,Kevin

Sorry for the delayed response

Ok the end part of the code -:08-E8 is the techincal numbers used by the ford engineers
I can find out tommorow exactly what these are they are normall for ie fault not present at time if test
But I will clarify the exact meanings for they numbers

I personally don't pay too much attention to these end codes/numbers and pay more attention to the actual code

P0299 is an underboost code
This code is set when the turbo boost pressure isn't matched at the MAP sensor (located on the inlet manifold ) will log this code ie the PCM actuates the turbo so pressure must be matched at the map sensor
So all the hoses /intercooler system must be inspected closely got any air leaks

Sticking turbo variable vane actuators are also a cause of this but as you have replaced the turbo this can be ruled out
On different Varients that have vacuum controlled actuators vacuum pipe chaffing can cause this issue but again as yours is an electronic actuator this can be ruled out

If the actuator/boost pressure isn't working correctly this gives you an underboost fault code

As I said the pipe work must have NO. Leaks as even the slightest loss of pressure before the MAP sensor

Also there is a air intake butterfly in the inlet side of the inlet manifold
Ensure this isn't being drawn closed by the vacuum regulator as this would differ boost pressure
You can dissconnect the vacuum hose from this butterfly to rule this out

Ideally a data logger road test should be carried out to measure boost pressure to see if it falls before fault appears

Kind regards XXXXX XXXXX

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