LF55 Nox Sensor Fault

UK PROFESSIONAL DRIVERS FORUMS THE UK PROFESSIONAL DRIVERS FORUM (INTERACTIVE)
1

Hi

I’ve got a 2011 LF55. The MIL lamp came on before Christmas. It seemed to come on just after washing it down for test.
My Delphi reads 3226-15 NOx sensor value too high (long term) active.

We had a Nox sensor in our stores so replaced it. Lamp still on and with MOT approaching sent it to our DAF dealers. According to invoice:
Connect to Davie investigate warnings. Found Nox sensor fault (long term). Re-programme ECU. Recheck - all faults cleared.

Picked vehicle up, all OK but then a few days later, lamp back on. Sent back to DAF. This time according to invoice:
Connect to DAVIE check fault and found air present at injector -OK. Run dosing tests and check quality of adblue - OK. Free off and remove rotten adblue injector returning nut. Clean injector (slight build up) crystallisation on tip. Clean threads on exhaust pipe. Refit injector with new nut. Reprogrammed engine ECU to extinguish warning lamp. Carry out road test. Ensure all plugs are dry for adblue system.

Picked vehicle up, all OK but then a few days later, lamp back on. Sent back to DAF. This time according to invoice:
Investigate emission warning light on. Connect to Davie found fault relating to CAT or mechanical failure of engine/inlet/exhaust as all other tests OK. Reprogramme ECU to extinguish light as requested.

It went for test the next day and the lamp stayed off. It passed the emissions also.

Lamp came back on after though. Still on now. Have replaced the exhaust with a reconditioned one and have also changed the wiring harness that goes to the Nox sensor and dosing unit. The old loom had a joiner missing and was full of dirt so thought we’d replace that as well.

I cannot extinguish lamp myself so not sure yet if the exhaust that I fitted yesterday was faulty or if we still have a problem. Does anyone know at what point will the MIL lamp go out on it’s own (if it does?)? Next tests I suppose would be compression tests? I’ve done pretty much everything else.

Oil and water are clean however the water level does drop occasionally. Cannot find a leak anywhere but exhaust smoke looks clean also.

There was a bit of smoke yesterday when starting up after fitting exhaust but it soon cleared, assumed it was just burning off. It’s been fine today.

The lamp was off last week for all of a day then came back on.

If anyone has any advice where to go next I’d appreciate it.

Thanks

2

Seems down on power now, and new active code reading 3226-0.

Any one?

3

Think you’re asking on the wrong forum, try posting in the owner operator forum.
I’ve no experience of daf but I’d be sending it back in and politely reminding them that you’ve already paid £x and the problems still there. Seems if it’s not the catalyst the only other thing it could be is the adblue pump? Have you disconnected the dosing valve and checked the amount of adblue being pumped?

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