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clueless
23-04-2007, 02:36 PM
Hello,

I've got a 2001 1.4 MKI4 Golf with 54K on the clock but only 10K on the engine. The engine management warning light illuminated last week. The mechanic at my local garage has a small hand held diagnostic tool which showed that the downside exhaust sensor was indicating the engine was running too lean. I think this is called a lambda sensor and is located downside of the cat. He reset the warning light and it ran for about 50 miles but has illuminated again.

Does anybody have a few pointers on what could be causing the fault. The office experts (?) suggest a dirty sensor . It seems that the front sensor can be fooled by a leaking vacum hose or temprature gague of MAF (I don't know what that is).

I'm loathe to have it hooked up to the main diagnostic machine which, on the two occasions I've had it done, hasn't properly pinpointed the fault. The last time I had it done the machine diagnosed a faulty coil rather than a fault which eventually led to a new engine and lots of grief until the warranty company paid up.

Thanks for any help.

Eshrules
23-04-2007, 03:11 PM
Hello,

I've got a 2001 1.4 MKI4 Golf with 54K on the clock but only 10K on the engine. The engine management warning light illuminated last week. The mechanic at my local garage has a small hand held diagnostic tool which showed that the downside exhaust sensor was indicating the engine was running too lean. I think this is called a lambda sensor and is located downside of the cat. He reset the warning light and it ran for about 50 miles but has illuminated again.

Does anybody have a few pointers on what could be causing the fault. The office experts (?) suggest a dirty sensor . It seems that the front sensor can be fooled by a leaking vacum hose or temprature gague of MAF (I don't know what that is).

I'm loathe to have it hooked up to the main diagnostic machine which, on the two occasions I've had it done, hasn't properly pinpointed the fault. The last time I had it done the machine diagnosed a faulty coil rather than a fault which eventually led to a new engine and lots of grief until the warranty company paid up.

Thanks for any help.

when the lambda sensor threw up a fault.... was it replaced?

clueless
23-04-2007, 07:50 PM
No. Didn't replace the sensor. The Mechanics advice was to give it a run to see if the fault appeared again. The tester he was using also has a code for a faulty sensor but the reading was for a lean mixture rather than a duff sensor.

Eshrules
23-04-2007, 08:08 PM
No. Didn't replace the sensor. The Mechanics advice was to give it a run to see if the fault appeared again. The tester he was using also has a code for a faulty sensor but the reading was for a lean mixture rather than a duff sensor.

from what i understand, the lambda/oxygen sensor is responsible for monitoring the amount of oxygen remaining in the exhaust gases. this information is in turn, relayed back to the ECU where adjustments are made real time to ensure the car is burning fuel at maximum efficiency.

if your sensor is faulty, it will give false/lean readings. i think there could be several causes for the fault reading you have. if it has only happend recently, i would derive from that alone that it would more than likely be the sensor itself.

i may be totally way off base, so please be patient and wait until a techie can get around to helping you.

in the meantime, you may wish to use the search function for lambda sensor :beerchug:

clueless
23-04-2007, 08:22 PM
Thanks for the assistance. I spoke to my friendly mechanic who is going to check the fault again on Thursday and see if it still has the same fault code. I've had a scan through some other forums and I'm not much wiser other than now knowing it could be a any one of a number of problems.

It might just be imagining another problem but I think my fuel consumtion might be poor - either that or i'm getting paranoid. I'll have to check it.

gmc
24-04-2007, 12:36 PM
Clueless, I've experienced and I am experierincing the exact same problem on a MKIV GTI (2002 1.8T). Last year it was plugged and diagnosed with two seperate VW garages and they could not identify the problem. The coils then went and a local garage replaced and fixed and the light did not appear on till recently. They checked it again and replaced 'a dump valve sensor' and the light remained off for about 500 miles, it is back on again and I am bringing back in tomrrow morning. The car runs fine but only slightly over-idles at traffice lights.

Will let you know what they say.

Eshrules, your posts are very informative . Thank you.

clueless
24-04-2007, 03:38 PM
I managed to get into the garage this morning. The initial fault code number was 1157 and referred to low oxygen on the downside sensorbut on the second reading was 1176. The hand held tester doesn't have this number in its index of faults although the mechanic thinks it is looking like the MAF air sensor could be the route of the problem. The engine is a little slow picking up. The fault has now been reset and cleared and his advice is wait until it lights again and have the engine properly diagnosed

dig776
29-06-2007, 10:03 PM
I managed to get into the garage this morning. The initial fault code number was 1157 and referred to low oxygen on the downside sensorbut on the second reading was 1176. The hand held tester doesn't have this number in its index of faults although the mechanic thinks it is looking like the MAF air sensor could be the route of the problem. The engine is a little slow picking up. The fault has now been reset and cleared and his advice is wait until it lights again and have the engine properly diagnosed

Watching this post with interest and reading all the helpful responses as my 1.8t is running lean too. Clueless can I ask when you say "MAF air sensor could be route of the problem" did you get it replaced?

Cheers

JK@golf.ie
01-07-2007, 10:42 PM
I had a similar problem last year but it was due to some sort of particulate in the exhaust which the sensors were picking up on. the warning sensor kept lighting up until it was fully cleared out. Took three visits but the mechanics assured me that it wasnt a problem even if the stuff was left there.

Flash2
01-07-2007, 11:32 PM
Clueless, I assume your mechanic put the car on the ramp and checked your exhaust system for leaks? That's the first step in diagnosing this fault.
When the car is new the back end of the exhaust comes in a single section from the CAT back to the tail pipe. If it has had a back box replaced at some point they cut the exhaust to save having to replace the CAT. Quite often the exhaust leaks where the new back box has has been joined to the original exhaust. If air is getting into the exhaust it will make the lambda sensor think the engine is running lean. As you said yourself, if the engine was really running lean (due to a vacuum leak, etc) then that would so as a fault with the upstream sensor and not the one after the CAT as in your case.
Dirty lambda sensors are very easy to clean by the way. All you need to do is disconnect one of your fuel injectors while the engine is running and give it a rev up. The cylinder that isn't firing sends a nice blast of clean air down the exhaust and blows all the muck out of the sensor. You'll end up with the engine warning light on mind you, so get your friendly mechanic to do it then clear the fault code.

Regards - Jim.