Car just failed MOT, CO emmision issue

**Bigdogcasa** · 19-05-2010,06:04 PM

My 1998 A4 Avant 1.6 has just failed MOT. Not many issues, just a wee leak at Rear Brake Caliper, hopefully just needing pipe tightened or new se , Ratchet on Hand-brake just stopped working, and main issue CO2 Exhaust Emmisions following Fast Idle, it passed on natural idle. The mechanic not entirley sure what issue was.

I had had issue with the Mass Air Flow Meter, and had disconnected it as it had been running badly. *** this made such a difference I had actually forgotten to replace it. We did run emmisions test with it disconnected and connected and on both occasions it failed. The reading was 0.683 on both first and second Fast Idle tests.

Could it be the MAFM or could there be any other reason for the CO2 reading to be too high on fast idle? What is the logical course of action to get to the of this problem.

Also the Hand Brake ratchet was working fine just a week ago and now if I try to apply the hand brake it works perfectly but no ratchet to lock it on. I have never dismantle a handbrake and the Haines Manual does not really seem to mention the ratchet element of the handbrake. Has anyone got any ideas what the problem could be and how to remedy? Could the fluit leak at caliper have any link?

Many thanks,

Doug

**kenney** · 19-05-2010,07:07 PM

a faulty sensor connected or disconnected,will not help the matter any

**STEWY L** · 19-05-2010,07:32 PM

the hand brake lever/ratchet would come as a complete unit i would have thought
(it's worn,and has no relation to the fluid leak),but should be pretty easy to
change.
as Kenney says, if a sensor is faulty, it needs changing for a sensor that isn't faulty,
the fluid leak could be a pipe,as you say, but it could also be caliper piston seals
which would probably work out cheaper to renew than to clean and re-seal,going on
labour rates these days.
hope you get it sorted without breaking the bank,
please let us know how you get on,
regards,
stewy.

**Crasher** · 19-05-2010,08:28 PM

The car cannot lambda regulate (to achieve the required Lambda 1 necessary for the catalyst to work) with the Air Mass Meter disconnected. Fit a new genuine Audi dealer sourced exchange AMM (DO NOT buy one from anywhere except Audi, no matter how tempted you are by fleaBay prices) and then have the ECU interrogated for fault codes. Have the codes printed out (including the one you have generated by disconnecting the AMM) and then have the codes cleared. Take the car for a good run (probably illegally now without an MOT) and then have the emissions re-tested. If the emissions are still too high, you will have to get another code read done and see which code (or codes) come up and compare this with the original code read and see if the same code(s) come up twice. NEVER even turn the ignition on with any sensor disconnected unless you can code read it first and clear the code you have generated afterwards.

**zollaf** · 19-05-2010,08:32 PM

hoping of course that running with a disconnected amm hasnt destroyed the cat already.

**Crasher** · 19-05-2010,08:42 PM

It should be OK but the lambda sensor may have suffered. I do not see cat failure very often although I did have a Passat 1.6 (same engine) in not long ago which had an AMM that had been disconnected for a very long time and even after a new lambda sensor, the cat would not recover at idle but was OK at fast idle. That particular car did not have a faulty AMM though, it had (I presume) a faulty lambda sensor and someone else had fitted two new lambda sensors but to no avail, it still kept coming up as a lambda heater circuit fault. I found that both of the new (and according to the manufactures listing, correct) Beru lambda sensors had too low a heater circuit resistance so the heater circuit was not consuming enough current. I fitted a new genuine sensor and it cured it (except that the cat was US) , sometimes pattern aftermarket parts can make your hair fall out…

**Bigdogcasa** · 19-05-2010,08:45 PM

Originally Posted by kenney

a faulty sensor connected or disconnected,will not help the matter any

If the Mass Air Flow Sensor will not make any difference, have you any idea what the problem could be?

**Bigdogcasa** · 21-05-2010,03:58 PM

Originally Posted by Crasher

It should be OK but the lambda sensor may have suffered. I do not see cat failure very often although I did have a Passat 1.6 (same engine) in not long ago which had an AMM that had been disconnected for a very long time and even after a new lambda sensor, the cat would not recover at idle but was OK at fast idle. That particular car did not have a faulty AMM though, it had (I presume) a faulty lambda sensor and someone else had fitted two new lambda sensors but to no avail, it still kept coming up as a lambda heater circuit fault. I found that both of the new (and according to the manufactures listing, correct) Beru lambda sensors had too low a heater circuit resistance so the heater circuit was not consuming enough current. I fitted a new genuine sensor and it cured it (except that the cat was US) , sometimes pattern aftermarket parts can make your hair fall out…

Hi Thanks for all the information.

Excuse my ignorance as I am not all that up on these sensors. but is the only way of checking which sensor is to blam by replacing it and if so should I get the lambda sensor fitted first.

I did a parts search and have had quote from a company to test and recondition the unit. As the car is quite old I really do not want to spend a fortune on it. Is this an option, and one company called said it was made by bosch.

Regards,

Doug

**Bigdogcasa** · 21-05-2010,04:53 PM

Originally Posted by zollaf

hoping of course that running with a disconnected amm hasnt destroyed the cat already.

Do you know if the CO2 reading is affected if engine not up to full temperature? The reason I ask is that the guy only ran it for a couple of minutes from cold before carrying out the test.

Doug