Troublshooting help for low power at low revs, EGR and turbo actuator faults

[liepinnssm]

Hi all,

Recently started to see some problems with my good old C5 X7.
Noticed a huge lack of power at low RPM (less than approx. 2500).

Citroen C5 (X7) / 2011 (VIN VF7**************[VIN obfuscated, can be read by forum staff])
Engine: DW12C_4HL / 2.2 HDI / 150 kW (204 HP)
Transmision: BVA AM6C


At first, I had no faults posted. However, after going for a drive and pushing the car hard I found the following faults:
P1462 - Fault of the EGR valve
P149C - Fault-turbo actuator
P2126 - Fault-air metering valve

I also noticed that the cruise control does not work when the engine is cold, don't know if it is related or another unrelated issue.

I reviewed some of the parameters in DIABOX and noticed a few issues.
One that stood out was the temperature downstream of the catalytic converter (or upstream of the FAP), which displays an invalid value but occasionally shows readings around +/- 80°C. Initially, I suspected the exhaust temperature sensor was the cause, so I replaced it. However, after measuring the resistance of the old sensor and comparing it to the new one, I found they were the same, and the issue persisted.
Another observation was the EGR electrovalve opening cyclic ratio, which reads -009%, seemingly out of range. It does, however, fluctuate slightly when I increase the RPM.
Lastly, I noticed a discrepancy in the turbocharging pressure. While the reference value rises with increased revs—reaching around 1400 mbar (3000 RPM)—the measured pressure only increases slightly, peaking at approximately 1080 mbar.

I am a bit lost as I can not connect the dots, so hope that someone on the forum can help me out.
I will appreciate the support!

[liepinnssm]

Update: Swaped the MAP sensor with friends car. No change in Turbocharger messured pressure, so it is not the pressure sensor.
So I believe that problem is with - temperature downstream of the catalytic converter (or upstream of the FAP). Can somone help me to understand which sensor is displaing this information - I am thinking that I replaced the wrong one or there is a wiring issue.

[liepinnssm]

Update: Replaced the temperature sensor PN 9675860880. When I measured the resistance for the old one, it read 0. Double-checked with the new one for which the resistance as it should be was not 0.
However, when checking the temperature data in the DIABOX after the replacement it was still showing the same: Temperature downstream of the catalytic converter (or upstream of the FAP) (Temperature at the particle emission filter inlet) - Value invalid. I assume I have to search for a wiring issue unless I am missing something.

[liepinnssm]

Update: Replaced Turbo solenoid valve as I found that there was no filter, just residue from filter material which made me think that it disintegrated and was sucked inside the valve. After messing around with the vacuum pipes and EGR vacuum actuator there was improvement in the power, however unfortunately after driving for a few days the low power came back. I guess I need to remove the EGR as it could be becoming stuck or there is a problem with the actuator.

[liepinnssm]

Update: Checked the EGR, it is clean and looks to be in order. Had the DPF washed, still low power, no fault codes when connected to Diabox and no lights in the dashboard. Next step to check Turbo, however, access is very poor and will require lowering of the frame. Did some tests via the diabox, when doing it for Turbo with the engine running, it showed that the "Air duct is disconnected", however, it checked with smoke, no leaks were found. The confusing part is why there are no faults, which should be the case if Turbo is blown or damaged and is not providing sufficient boost.

[liepinnssm]

While trying to prepare for the painful turbo and pre-cat removal, I was trying to solve the invalid temperature value. I am sure that this is the value provided by the sensor located inside the DPF with the brown connector (while connecting the old sensor and heating, the value was getting slightly higher, however, still flickering from some low value to an invalid value). However, the sensor replacement did not solve the problem. I checked the wires on the harness, and all seems good, both neutral and positive are fine. I am not familiar with the logic behind the indication except the fact that the ECU is monitoring the Voltage change and, based on that, displays the temperature. Maybe someone can help me to understand if there is something in between the sensor and ECU.

[citroenguy]

Usually there isn't anything between the ECU and sensor, possibly a connector.
The best would be to load test the circuit.

However, after reading your first post.

Are the fault codes permanent?

Im suspecting stuck VNT vanes or faulty actuator or possibly failed MAP sensor

Is the turbocharging pressure always the same?

[liepinnssm]

Usually there isn't anything between the ECU and sensor, possibly a connector.
The best would be to load test the circuit.

However, after reading your first post.

Are the fault codes permanent?

Im suspecting stuck VNT vanes or faulty actuator or possibly failed MAP sensor

Is the turbocharging pressure always the same?

Hello, thank you for the comment.
After I washed the DPF, there are no faults at all, even if I push the car hard, nothing is posted, no underboost-related fault, etc. I have a feeling that the car is in some kind of safe mode, and the ECU is aware of it, therefore sees the underboost condition as normal and is not using the turbo due to some protection. That's why I am focusing on this invalid temp value (which is not constant and flickers from something like 60-80 degrees Celsius and an invalid value), as I think that due to the unknown temp at the exhaust, it is protecting the engine. I checked the connector for the temp sensor; both wires are good, even connected the 3rd sensor I had spare to double check that it is not the sensor fault. I got access to the turbo compressor, blades spin freely, no obstruction as much as I could see, no missing or damaged blades. I am 100% sure the problem is not with MAP or any other component downstream of the turbo, as with higher speed (which is more airflow delivered to the engine), MAP is rising, and at 150 km/h it reaches the reference value for the turbo, and the engine is very responsive. So I definitely think MAP is good; the issue is with a lack of air. However, I am not confident that the problem is mechanical and with the turbo itself, as I don't have any fault codes, which should be the case if the turbo does not produce enough boost when it is required. I have a turbo with an electronic actuator, and it is not stuck, moves freely and passes the tests via Diabox. I am completely lost and afraid to go to the local garage as I think that they will just do some unnecessary, expensive repairs without solving the issue.

[citroenguy]

Is it only flickering between invalid and 60/80° with a cold engine?
It could be the default value until the temperature comes into normal range.

Does it show a reasonable value with warm engine?

[liepinnssm]

Is it only flickering between invalid and 60/80° with a cold engine?
It could be the default value until the temperature comes into normal range.

Does it show a reasonable value with warm engine?

The same applies to a warm engine. When cold it is around 60, when you start the car a little bit over 80, have not seen it go any higher. I also checked the value on a friend’s car with the same engine, and even when cold, it shows a normal reading that steadily increases as soon as the car is started.
I am wondering if it could be an issue with ECU.

[liepinnssm]

Today, checking for fault codes and looking at engine data, as I had a feeling that the car is a little bit more responsive than usual, I found P0215 [Fault control main relay].

[citroenguy]

If the wiring is OK (eg load test with a 21W bulb), there could be an issue with the ECU.

But, have you tested the EGR with diagbox? Seems to be an odd thing with both vacuum and a electric valve.
Just thinking if the EGR somehow is always a bit open. That would explain a mass airflow code