Directional headlights & MAF fault

[vallium]

We're talking about Citroen C5 X7 2.0 HDi VIN VF7**************[VIN obfuscated, can be read by forum staff]

It's throwing codes both for non-functioning MAF and no communication with directional headlight computer. This is from generic Delphi scanner, I don't have data from Diagbox at hand

Engine electronics

P0102 - Flow sensor signal. Frequency exessive: min air flow
- Permanent

Multifunction (Body computer (BSI) (Body computer) - Diagnose)

089 - No communication with directional headlamp ECU
- Permanent
- Not characterized


MAF is on diagnostics showing sensible air temperature and 0 airflow during idle that blips a bit if you raise the revs. Directional headlight computer is not communicating in any way.

They're both on the same fuse that I'll check tomorrow (F6 in engine room) but together with some diagnostic port that seemingly works just fine, so that's weird. Otherwise perhaps common ground?

[GiveMeABreak]

Fault Code:	P0102
Description of Fault:	Flowmeter signal: Measured flow less than the minimum flow. The ECU detects a drift of the air flow signal: The period of the signal for air flow measured exceeds the maximum threshold of 65535 µs corresponding to the minimum threshold for air flow. The fault appears at the end of 300 ms.
Conditions for Fault to clear:	Ignition on
Downgrade Modes whilst Fault is active:	Deactivation speed limiter until the next time the ignition is switched on Deactivation cruise control until the next time the ignition is switched on Deactivation of the forced regeneration of the particle emission filter The ECU stops the regulation of the EGR valve
Symptoms:	Smoke from the exhaust
Suspect Areas:	Air flow meter Electrical harness Engine ECU

BSI Code should be F089 and that is Fault: no communication with the directional headlamps ECU: Not characterised, so has no further detail.

[vallium]

Good news: It was the fuse.

Bad news: New one blows after replacement.

Next stop auto electrician I guess.

[GiveMeABreak]

At least you have pinned it down. Likely an exposed wire along the way causing a short.

[Doo]

The thing with a MAF fault is it's not necessarily the MAF itself that's at fault. In a Turbo Diesel, it can be a hole in the intercooler (very probable) or a burst hose or even (as I experienced a few year back), bought a FIAT with a "blown turbo" which was actually a rusted worm drive clip on the lower intercooler.... 23p for a pair of clips and the fix was complete

It's a bit of a mare to check the cooler in place, but sometimes you can hear it hissing if you're lucky. It's almost always caused by a sharp stone.

[vallium]

Update now that saga is over:

Fault was most probably in steering mechanism of left headlight. Don't have wiring diagrams but all signs point to mechanism being on same fuse as computer/MAF.

Went fault hunting with some noname fuses. One or two blew but then magical smoke released from headlight, fuse was not harmed Since then main beams worked again, right headlight could be steered via Diagbox, left one didn't respond.

After some digging I found a guy on drive2.ru who disassembled Valeo headlight from some Volvo. Apparently grease gets hard with age and whole mechanism difficult to move. Fix is to open the headlight and regrease everything, pretty serious surgery.

Anyway my mechanism was already fried but I found both lights from 2014 model year for cheap. Post facelift but installation was pretty much plug'n'play as mentioned in another thread:

viewtopic.php?p=764840

And of course some Hella fuses.

Lesson:

Do not use noname fuses if you don't want to fry electrical components.

[GiveMeABreak]

I did some checking and Fuse F6 in the engine fusebox does supply the MAF and the Dynamic Beam Adjustment Unit for the Directional Headlamps, so this is why there was an issue. Did you replace the F6 fuse with a higher Amp? If so, that may have caused the damage, but otherwise I agree, get decent fuses. Thanks for the update.

Incidentally, how did you get on with the later lamp DRL having an LED strip and the configuration?

[vallium]

Did you replace the F6 fuse with a higher Amp?

No, red fuse, 10A.

Incidentally, how did you get on with the later lamp DRL having an LED strip and the configuration?

I believe it worked out of the box. At first I just replaced failed headlight and everything was alright, no more blinking dipped beam signal light, codes could be cleared. But didn't check for functioning of the LED strip. It illuminated just don't know how strong and when.

After I set things as I believed they should be (combined daylight/side beams & some other setting) illumination sensor got borked, Xenons worked all the time. From there it was a bit of "What does this button do?" situation, but I believe I ended where I started & everything works correctly now.