Limp mode when towing caravan

[gedhart]

Really need some advice please. Our 2005 D5 163 XC90 recently went into limp mode (without towing the caravan). It was an intermittent fault and tended to happen when putting your foot down, but not always. Warning message in car - "Engine Service Required"

The following codes came up:

1300 permanent - Mass air flow sensor circuit invalid signal
9210 intermittent - ECM 9210 cruise faulty signal
9520 intermittent - Accelerator pedal sensor PWN-signal incorrect
6805 intermittent - Boost pressure regulation, incorrect flow

After resetting the codes, when it happened again, the last code remained:

6805 intermittent - Boost pressure regulation, incorrect flow

One Indie garage did some tests and deemed the turbo to be knackered. We took the car to another local Indie and they checked the turbo and found it to be seized, so they replaced it at a cost of £800. All seemed well until we hooked our caravan up and after around 30 mins of driving, the car went into limp mode again.

It's obviously something that happens when the engine is warm and usually when climbing a bit of a hill. The car certainly feels livelier with the new turbo, but I'm worried at the spiralling cost and hassle of trying to diagnose it, and test with at least a 30 minute drive with the caravan each time.

It's simply dangerous to tow with reduced power as we're scared of overtaking anything. Please help!!

EDIT: I forgot to mention that I gave a list to the garage of possible faults:

* dirty fuel filter
* EGR valve clogged
* leaking vacuum engine mounts
* turbo vanes stuck
* cracked turbo pipes
* turbo control solenoid
* cracked or corroded intercooler
* turbo inlet hose split
* fuse #11 in engine bay fuse box (EGR valve, VNT, vac mounts, PTC valve, and more…)
* faulty battery

Obviously some of the turbo related stuff doesn't apply now, having had a new turbo fitted. The garage checked one of the vacuum engine mounts had no pressure, so they temporarily blocked it off. Been driving around OK for the last couple of weeks but we drove 40 miles with the caravan at the weekend and it went into limp mode on both towing journeys, but not inbetween.

[Coldrow]

I had a similar problem earlier this year although mine is a 2006 car so the 185bhp engine.

I wouldn't rule out the MAF sensor. Mine would go into limp mode when the heat in the engine bay got past a certain point. For example when stopped in traffic or when the engine was under increased load, like towing. My theory was that the extra heat pushed a marginal MAF beyond what the ECU could accommodate so would trigger limp mode.

If you can get the car hooked up to VIDA and take some readings for the MAF at tickover it should give you an indication of it's health. Somewhere in the region of 47Kg/h (without going back to check) is what you should expect.

[Tannaton]

Boost pressure regulation problems are usually a cheap-ish fix. If the car is going into limp mode it is usually overboosting - i.e. too much pressure.

The boost pressure is controlled by a variable vane in the turbo itself which is controlled by a vacuum operated actuator. The vacuum to the actuator is controlled by a Turbo Boost Control valve which lives at the front of the engine behind the starter motor. Have a search of this forum and a Google for all these components so you know what they look like.

Common problems are (in no specific order) that :

- The pipework becomes damaged/disconnected
- The Turbo Control Valve fails (£120 part - cheaper pattern ones available)
- The engine mounts fail (the engine mounts are also vacuum operated and if the system for them fails, there might be insufficient vacuum to operate the turbo control system).

Try some diagnosis that costs nothing first - there are articles on doing these processes in this forum:

- Check and follow all of the pipework
- Disconnect and plug the vacuum engine mount system, then drive the car.
- Bypass the TCV and connect the actuator directly to the vacuum - the car should drive with no boost - i.e. you can use the full rev range but feels like its on half power. This would indicate that the vanes are not seized.

Can you get the car to go into limp home mode without towing the caravan, but by thrashing it?

[gedhart]

Thanks, Coldrow & Tannaton. Since the turbo was fitted, I haven't been able to get it to go into limp home mode without towing, but I haven't thrashed it for any longer than around 20 mins.

The garage checked the vacuum engine mounts and there was no pressure - they've blanked off one of the engine mount pipes.

[Tannaton]

Originally Posted by gedhart

Thanks, Coldrow & Tannaton. Since the turbo was fitted, I haven't been able to get it to go into limp home mode without towing, but I haven't thrashed it for any longer than around 20 mins.

The garage checked the vacuum engine mounts and there was no pressure - they've blanked off one of the engine mount pipes.

By thrashing it I mean sustained full throttle - try driving the car in manual mode, putting it into fifth as soon as you can and floor it until you can't go any faster for safety/legal reasons - if you are on a dual carriageway you should get a good few seconds plus at full boost.

[gedhart]

Thanks. I'll give that a whirl tomorrow, Tannaton!

[gedhart]

Unfortunately @tannaton, thrashing it didn't put it in limp home mode. Took it on a motorway and booted it in 5th.

I'll take it back to the garage and mention your diagnostics. I'm currently running with one of the vacuum engine mounts isolated and plugged, as the Indie reckoned there was no pressure there.

[Shadeyman]

P0244 BOOST PRESSURE CONTROL - FAULTY FLOW
ECM 6805

Diagnostic trouble code (DTC) information

Condition:
Diagnostic trouble code (DTC) ECM-6805 (P0244) is stored if the boost pressure deviates from the desired boost pressure for the engine control module (ECM).


Substitute value
-Engine speed (RPM) limitation.


Possible source

Flow too low or too high:
-Leakage in the vacuum hoses for the engine pads
-Leakage in the engine pads
-Air leakage in the intake system
-Leakage in the vacuum hoses to the turbocharger (TC)/turbocharger (TC) control valve
-Blocked hoses for the turbocharger (TC) / turbocharger (TC) control valve
-Damaged turbocharger (TC) control valve
-Damaged turbocharger (TC).


Fault symptom[s]
-Poor performance.


Checking the component
-Ignition off
-Check that all hoses connected to the solenoid for controlling the engine pads are correctly installed, are not leaking and are not blocked
-Check the engine pads for leakage
-Check the connector for the variable nozzle turbo governor. Check for contact resistance and oxidation. Check that both the hoses connected to the variable nozzle turbo governor are correctly installed, are not leaking and are not blocked
-Check the pipe between the turbocharger (TC) and the intake. Check for leakage
-Reinstall the connectors, components etc.
Remedy as necessary.


The MAF measures the amount of air passing through it. If, when compared with other measurements(boost pressure, RPM etc) the ECM deems it to be abnormal limp mode is engaged.
The primary fault is a leak somewhere on the turbo system, between the MAF and the inlet manifold, or the turbos vacuum control system. Replacing the vacuum pipes that control the turbo is cheap and easier, quickly rules out a leak. A leak on the turbo intake side can be difficult to find but will cause limp mode just like a leak on the exit(high pressure/boost) side.

[gedhart]

Thanks Shadeyman. I'm putting the car into the garage next week, so will mention your post. The car only goes into limp mode after approx. 30 mins of driving while towing. If it was something physical, wouldn't it occur any time the car tows? Could it be something that kicks in when the engine gets to a certain temp?

[gedhart]

Just closing the loop on this thread, in case it helps others.

The garage has replaced both the MAF & MAP sensors (we were only charged cost price of £61 for the MAF sensor; not charged for the MAP). Not sure if it's either one or both, but we've since towed the caravan on a longish journey and it didn't go in limp home mode.

Thanks all for your contributions . I can breath a sigh of relief, as I thought it would be a long drawn out battle to get to the bottom of it. If this wouldn't have worked, we considered selling the car, as it needs to be able to tow our caravan safely.

Hope that helps others suffering similar symptoms.