First of all I'm from Sweden so I hope you can understand me. It´s also a quite a lot of text but I wanted to be sure that I mentioned everything that I have tried
.I just registered on this forum but have owned my 406 for a couple of years now and been sneaking around here without registering me.
The car in question is a 2001 406 2,0 HDI that has covered almost 490000km / 300000 miles.
The engine is equipped with an "box" which is said to increase the power from 110hp to 130hp.
With regular service and maintenance it has been running fine until last week when my parents borrowed it for an summer holiday trip.
It started with the engine light on and a lack of power and they went to a local garage and got the following codes:
P0100 Mass or Volume Air Flow Circuit Malfunction
P0235 Turbocharger Boost Sensor A Circuit Malfunction
P0246 Turbocharger Wastegate Solenoid A High
P0568 Cruise Control Set Signal Malfunction
The codes were cleared but the engine light came on just a few km later.
They then went and bought an WIFI ELM327 reader and got the following code when connected to an iPad with an OBD2 App:
P0243 Turbo charger wastegate solenoid malfunction.
In the free app it wasn´t possible to reset the codes so they kept on driving with the engine light on.
A few days later the engine light went off but it still lacked power.
They also noticed that the brake servo kind of "hesitated" some before it started to assist the brakes.
At first the pedal was very firm/hard but then the servo action kicked in.
I have noticed this braking problem a few times before but didn´t take any notice of that.
In the beginning of this week they drove back home again and the engine light came back on.
It had now started to lack some serious power, they had to change down at least one gear when reaching steep uphill's at motorway speed, which had never happened before.
When they arrived home I checked the codes and again it got the P0243 Turbo charger wastegate solenoid malfunction and also an P0903 Clutch actuator circuit high.
I believe the last one came up when they drove it up on our driveway which is really steep and not funny with an 406 that lacks power.
I cleared the codes and took the car for a drive and it was unbelievable slow.
I checked the live values and it was first at over 4000rpm that i got some real turbo boost, the intake manifold absolute pressure reached 170kPa at 4500 rpm.
There were no sudden boost increase, it was more a slow increase during the whole rev range.
The brake servo was also acting strange with poor servo assist.
It also produced some serious black smoke.
No engine light came on again but I got the P0243 Turbo charger wastegate solenoid malfunction in the system once more.
To sort this out I have tried/done the following things:
Cleared the code again.
Treated it with new oil, filter, air-filter & fuel-filter.
Disconnected the MAF with no difference.
Checked all piping from the turbo to the intercooler and to the inlet manifold and it all looked okay
Checked the intercooler of any signs of damage or clogging and found neither.
Switched vacuum valves between EGR and turbo with no difference.
Cleaned the above valves air filter with no difference.
Checked that the wastegate moves easily which it does.
Changed all vacuum hoses.
Checked the one way valve on the servo and air flows freely in one direction and I can hear a tiny leak in the other direction.
I then plugged all vacuum hoses except the one that goes to the wastegate, and hey presto the boost was back where I wanted it.
I borrowed an vacuum meter and measured the vacuum on the hose that goes to the wastegate and it maxed out at around 45cm HG.
I then reconnected all vacuum hoses and checked the value again on the hose that goes to the wastegate and it barely showed a value.
With the engine idling I pushed on the brake, it first was very hard but then the servo action kicked in.
At the same time i saw that the vacuum value on the gauge slowly raised until it maxed out the meter.
I then removed the one way valve, still connected to the vacuum hoses, and held a finger on the servo side of the valve and immediately the vacuum meter maxed out.
Almost immediately after I switch of the engine the brake servo assist disappears. I have read on the forum that some cars have some servo effect left even the next day.
All this leads me to believe that I need to change the brake servo, do you agree or do I have more things to try ?
Thanks in advance !
Viktor from Sweden.
It does sound as if, at rest, the servo vacuum is open to atmosphere and this is closed off once the servo is in use allowing the vacuum to rise. This would indicate some sort of problem inside the servo, I seriously doubt you can open it up to investigate so yes, I agree, the servo is toast.
