Z4 2.0 Codes P0112 and P0420

N

narbles

Member
Unfortunately our 2005 Z4 that we bought 3 weeks ago has thrown up another set of codes. At least one problem per week...!

Previously, we had the P0420, the dealer sorted this by replacing the O2 sensor on bank 1 and also replaced the rocker cover gasket. Before this they replaced the coolant expansion tank and then before that they replaced a coolant hose that broke.

Now we are about 40 miles later (and a few days) since the latest work was done and the car has now thrown a P0112 code (Intake Air Temperature Sensor 1 Circuit Low) along with a P0420 code. We will be contacting the dealer again tomorrow but what sort of issue are we looking at? Is the car a dud? Should we be thinking of rejecting it?

For info it's done just over 60,000 miles and appears in good nick inside and out for the most part.
 
So I've done some more reading up on this and it appears the MAF/IAT unit just after the air intake is going to need replacing. I suppose my question now is why would the P0420 code come up again with this?
 
The p0420 code is a common one on the 2 litre engine.
If the MAF or IAT are bust, that can result in miss-fueling which inturn can throw the catalyst code. It is likely a symptom and not a cause, one that should probably be ignored for now.

Check the live data from a code reader to determine if the IAT is knackered. It is not a particularly common failure but they certainly can fail.
Clean the connectors with a quality connector cleaner/protector. Years of dirt and vibration causes many electrical gremlins :thumbsup:
 
Jfgoldfish said:
The p0420 code is a common one on the 2 litre engine.
If the MAF or IAT are bust, that can result in miss-fueling which inturn can throw the catalyst code. It is likely a symptom and not a cause, one that should probably be ignored for now.

Check the live data from a code reader to determine if the IAT is knackered. It is not a particularly common failure but they certainly can fail.
Clean the connectors with a quality connector cleaner/protector. Years of dirt and vibration causes many electrical gremlins :thumbsup:
Click to expand...

Thanks for the response. When you say it should probably be ignored for now, why's that?

Contacting the dealer this morning though this is the 4th or 5th time we've been back to them with problems. They've actually been very good so far but I'm wondering at what point they will be sick of hearing from me...
 
The p0420 code often appears as a symptom of other problems or when the car hasn't been driven hard for awhile. It might be worth checking that the exhaust manifold doesn't have a small crack in it but it certainly isn't worth throwing time and money at it if no issue is found. It is a quirk of the 2 litre engine management; the catalyst monitors are a little too sensitive.
If the car is running ok, the catalyst code will clear itself after 2 or 3 clean drive cycles.
This code can muddy the waters when diagnosing problems, leading to work being done that isn't required.
 
Yep, agree with thoughts shared by goldfish above. I have the same 2.0 litre e85 and had the same code. Read comments by forum members and seemed clear that bimbling around on local sedate drives / stop start town driving is not ideal for this engine. I used Catacleane once and now make sure my drive includes some faster /higher revving parts and the code has not reappeared. It can be a sympton of other problems which shouldnt be ignored i guess but csn also perhaps simply be a foible of this particular model. Good luck resolving this :thumbsup:
 
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