Thread: 2011 D4 'Gearbox Fault' warning

Cheers Jeffoir
Yes, under the green tarp in the rain!

I just drove 3h home from where we spent easter and got within the last 30 mins before the red triangle followed by the yellow triangle followed by Gearbox Fault followed by Restricted Performance.

I had the iCarsoft hooked up monitoring the 'Fuel Pressure' (more on that in a sec) so I did a scan, 2 faults were recorded: P117D "Fuel volume regulator exceeded maximum control limit" and U2023 "Fault received from external node". I restarted and drove on. 2 Gearbox Faults later and we're home.

Interestingly I reckon the car felt underpowered at times which is something I haven't really noticed before. In fact the second fault occurred pulling away uphill from lights. The car was definitely sluggish then on the 1st to 2nd change it crapped out.

Before setting off I set the iCarsoft to display live values for the fuel pressure. At least I checked the Fuel Pressure box in the list of options. The first thing I noticed is that the values jump all over the place. At idle the values fluctuate from about 25 to 32 ish MPa. When driving the values under moderate load were fluctuating between about 72 to about 85 MPa. Up the Mt Ousley hill with the foot down (probably 80% throttle) I saw the values jump into the 98 to 120 MPa range. Coasting along the values danced around 42 MPa.

Assuming this 'Fuel Pressure' value is the relevant value a) is this fluctuating normal b) do these values sound normal?

The hpfp fail codes include

Engine TDV6
•P2290-00 (6C) Injector control pressure too low

P0087-00 (2F) Fuel rail/system pressure - too low

Originally Posted by Bananas

Assuming this 'Fuel Pressure' value is the relevant value a) is this fluctuating normal b) do these values sound normal?

Completely normal. Fuel pressure is ramped up as torque demand & RPM increases and fluctuating values is absolutely normal.

As a complete WAgeneralization the failure mode on these appears to be when there's a moderate demand (like cruise control on the freeway) and a slight increase in power is required. The PCV is commanded to "open a bit more" and it sticks. If you were to drive manually and every throttle request was a decent stab it doesn't tend to happen. I guess you can't do that with an Auto because it'll kick down.

When it sticks, if you happened to be watching your PCV vs Pressure graphs you'd see the PCV command spike. On mine I set an alarm in the GAP to beep when the PCV >= 50%. It almost never gets there under normal driving, but when it sticks the ECU winds it "fully open" and after ~2 seconds of not seeing an increase in fuel pressure you get the fault. If you get off the throttle and stab it back on again before the fault registers you've avoided it that time.

Of course yours might be different. When mine first started to play up I was seeing VCV faults, but within 2 or 3 faults it always came down to low injector pressure and was the PCV sticking. One day when I get a moment I'll strip the pump I have here and dismantle the valves for a look. I've been saying that since 2019, so don't hold your breath.

@PerthDisco I haven't seen P2290-00 or P0087-00 (yet?)

@BradC I'll order a GAP iiD today to try to get a better picture of what's going on.

Thanks again guys. I would still be on the hunt for gear box problems. if it was not for your suggestions.

I’m not convinced you’ve got hpfp problems just yet especially with the rev surging issue

Cheers PerthDisco

I drove today and tried to focus on the surging to see if how I previously described it is accurate. It seems like it should be easy one but I cannot say for sure whether it's a monetary power cut or power increase. I'm almost certain it's momentary power cuts because it really does feel like a petrol engine missing. One thing I noticed is that I over stated the degree to which the tacho needle bounces. I said earlier it was bouncing by about 500 rpm. From what I observed today it's more like 200 rpm and it bounces both sides of the rpm I'm driving at; lower first then overshoots then settles on the actual RPM, then repeats until I put my foot down a little or shift to S. In S it is only slightly noticeable, but I previously said shifting to S stopped the surging altogether. What is certain though is that the surging occurs as the load on the engine increases. I could not feel the surge coating on teh flat or down hill, only up hill.

I read more about the P117D fault and learned this relates to the fuel volume control valve (VCV) which is one of the cans permanently crimped on to the HPFP. From what I understood, the P117D fault indicates that the VCV is either receiving too much or too little fuel from the lift pump.

I haven't tested the LPFP yet, so that can be this weekend's treat along with a new fuel filter.

FWIW bananas, I suspect you might have 2 issues.
1: HPFP.
2: Torque converter, this one can be temporarily ameliorated by changing the fluid and adding 2 tubes of lubegard shudderfix, this may not work if you're towing heavy though.

Yes I think you have the dreaded HP26 gearbox torque converter issue along with a failing HPFP. Both common issues.