Intermitten, sudden power loss, DSC light on

[RenoHuskerDu]

Our 3.0d facelift acted up today. First came a dramatic power loss at about 85mph, with DSC and general fault (see pic below) lights on. A warning text came up: "DSC/4x4 inactive" but only for about 5 seconds. I coasted off the road to a safe spot, and noticed a high and unsteady idle of 1500rpm. Throttle application had no effect.

Shut down, remove the RaceChip via its shunt, restart, problem still there. No power. Or so I thought.  Call wife, arrange pickup, plan to get my E70 and big trailer, morning plans all shot to hell now. Decided to limp the E53 to a safer spot for loading the trailer. Restarted to do so, and suddenly nothing was wrong anymore.

Decided to man up and continue our plans. Called off the wife before she left home. Left RaceChip shunted out. Headed out, feeling plucky.

5 minutes later, the problem returned. Then I discovered that the fault mode's high idle could be used to move the car quite smartly by upshifting at 1500, as long as I don't hit the accelerator. Top speed was about 45mph, OK for back roads. After our morning plans were done, we limped home on back roads.

So the fault comes in and out willy nilly. The car will have full power for a minute or longer, then go into fault behaviour. Fault mode lasts for a minute or so. As we drove for about a half an hour, it seemed that the car toggled faster between normal operation and fault. Sometimes it was just a few seconds.  There was at times a faint clanking noise associated with the fault appearing. This could merely be driveline snatch.

So I googled around a bit just now and came up with these possibilities:

1) MAF has had kittens. This makes sense to me. I've had MAF issues in other cars. Weird symptoms.
2) Perished vacuum hoses to EGR and Turbo controller. This doesn't make much sense as the fault is very intermittent.
3) Fuel filter restricted. Pretty sure we just changed that. Again, this does not match intermittent.

Any other ideas?

Here is a pic of the dash warning lights.

[themoog]

I think your ABS module is at fault. That yellow cog sign is transmission safe mode and that's where the power loss is. My old E39 had similar symptoms.

[X5Sport]

What 'cog' symbol?  I can see a yellow brake system warning?  Different pic?

ABS looks likely but the rpm bit worries me as that would not be affected by an ABS issue - or at least I can't see an obvious connection.

How are the shifts in all gears?  Does it do it in manual?  When my torque converter went I had weird rpm issues and intermittent shifting and power loss due to loss of oil pressure in the gearbox - and clanking noises!  I got no warning lights until the box itself failed.

[themoog]

Youre right. There is no cog sign. Why I mentioned that I have no idea- possibly San Miguel.

[RenoHuskerDu]

Correct, there is no cog light, and it's a manual transmission.

Results of reading codes today are numerous but the high pressure fuel rail sensor stands out.  There were too many codes logged, making it difficult to suss out what it was.  At least he cleared out all the codes. I suspect it will come back and then we'll be able to see what it is. The high pressure fuel rail pressure sensor seems to be the most likely culprit at this point.

The problem went away on the drive to the indy, natch. And a brisk drive this evening was also uneventful.

[X5Sport]

Eliminates the auto box too....

Weird that a fuel issue would throw a DSC and brake warning though!  I mean one is go, the other is stop. :'(

[RenoHuskerDu]

Is that the brake warning light? Wow, that is odd, indeed.

[X5Sport]

Dynamic brake system fault or ABS system fault.  DBS is the extra brake system that takes over when you apply emergency braking.  Andym3 has just had the same warning on his E46!

As it's Amber you can continue to drive.  Anything showing if you press the 'Check Control' button in the binnacle?

[RenoHuskerDu]

I noticed that nothing shows when I push on the stalk. Usually errors are muted there, with small yellow arrows on the sides of the display to indicate there is something more if you push the stalk.

Now, is that the 'check control' button? I'm not sure and darkness has overtaken France for now.

[RenoHuskerDu]

I have an update on the situation. I ran with the racechip installed and had no problems for about 5 days but then it came back. I went in to pull the codes and surprise,  the codes are different. There's no high pressure fuel rail anymore, there's a message about fuel control synchronization. I called Racechip GmbH and they told me they've seen this issue. They gave me suggested new settings for their module. I'm going to run with it shunted out for about a week and then plug it in again, and I will keep you posted.

Meanwhile it keeps acting up now on the way home.  I'm starting to get pretty good at driving it in this pseudo limp home mode. Fortunately the Boost comes on at about 1300 RPM, or I'd be Fritos. My power band is about 300 to 400 RPM wide! I've always enjoyed a challenge.

If past behavior is a good predictor, it will stop acting up soon and I'll be able to drive other week with no worries. Back in my own driveway as I finish this post,  the problem has gone away for now. If the RaceChip is causing the problem I should have no more worries until I plug it back in.

[RenoHuskerDu]

When I press check control it just says Check Control OK

[RenoHuskerDu]

I stewed on this for some time and found the cause. The problem did not go away after shunting out the RaceChip. It hit every day, every drive, unpredictably.  I remembered that the problem went away for 4 days after I had removed  the motor cover and blown away the dust with compressed air.  I came to suspect that it was something physical under there.

So I pulled the cover off again and had a long peer into things. Lo and behold, I found the wiring harness for the RaceChip up against the EGR valve, with its insulation knackered by the heat. Two wires were making contact.  The fix was unremarkable; repair the insulation, install additional split loom, and re-route the harness.

So at the end of the day, neither the car nor the RaceChip was at fault. It was my own careless installation!

[Colin]

Phew ! relief i would say  a cheap and easy fix