VW Lambda Sensor Problem

2.0 Bora (AQY)

Recently the Engine Light came on & I've diag'd with VAG-COM, had 4 faults codes as follows:

16556 - Fuel Trim; Bank 1: System Too Rich

P0172 - 35-00 - -

17536 - Fuel Trim; Bank 1 (Mult): System too Lean

P1128 - 35-10 - - - Intermittent

16518 - Oxygen (Lambda) Sensor B1 S1: No Activity

P0134 - 35-10 - - - Intermittent

01039 - Coolant Temperature Sensor (G2) 30-10 - Open or Short to Plus - Intermittent

Replaced Coolant Sensor(£28), MAF(£56) & Bank 1 Lambda Probe(£78) all Parts from my local VW stealer. Problem now is the Lambda probe shows working on idle till move away & the voltage & signal drop to zero.

Acceleration is rough & the car is running lumpy. Am I missing something or is the Bank 1 supposed to switch off during normal driving?

Reply to
A C
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What age is the car?

Under load/acceleration, the lambda should show that the engine is running rich (ie show a voltage). Sounds to me like you've got a bad connection somewhere.

Reply to
M Cuthill

The car is a 2001 Bora 2.0 Petrol

I've included a attachment of the VAG-COM Measurements, as I thought the same but it shows it working until you touch the accelerator

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Reply to
A C

POtentially you've got an air leak. Have you tried Vag-Coms forums, they're normally quite good at these.

Reply to
Duncan Wood

Yes, I have posted the problem on the VAG-COM Forum & a couple of other forums just to see if I can finally get to the bottom of the problem.

Why would an air leak cause the sensor to sit at zero?

Reply to
A C

This might be a stupid question, but did you change the right lambda sensor?

By the looks of your fault codes, the pre cat sensor has gone faulty (code P0131), and this has been picked up by the post-cat sensor (code P0172). Note that both those codes start with P0 which indicates an emmissions related concern, the P1 code is a manufacturer specific code (a lean situation is of less concern to those who set the limits than a rich one).

The post-cat sensor should produce a relatively steady output, which indicates the pre-cat sensor and the cat are doing their job. The pre-cat sensor should be constantly changing when the engine is held at a constant speed, should show high voltage when engine is under high load/accelerating, and low voltage when on overrun.

Plus all that could be caused by an air leak, in either the inlet system or the exhaust, which can be enough to upset the system.

Reply to
Moray Cuthill

Which lambda sensor did you replace?

Is the lumpy running rich or lean What do the plugs look like?

Tim..

Reply to
Tim (remove obvious)

I change the one on the manifold & the spark plugs are brand new

No obvious air leaks, lumpy running on lean

Reply to
A C

Either the MAF is still wonky, or you have a fairly serious air leak between the MAF and the throtttle body.

Is the ECU entering closed loop running at all?

Can you artificically make it enter closed loop to prove the o2 sensor will switch and the ecu respond to it?

(un-lit propane torch is very handy here to supply extra fuel)

Tim..

Reply to
Tim..

Because there'd be lots of fresh air getting in to the O2 sensor, which will give a "lean" output, due to all that unburnt O2...

Reply to
David Taylor

BMW 318i 1992 that used to run beautifully.

I have rough tickover and lack of low end power and a slight exhaust leak. The ECU is saying there are no faults. I've changed a hell of a lot of stuff to try and cure this problem.

Could the exhaust leak really be the problem? (I appreciate you've said exactly that above but I'd prefer working on engine stuff before I replace/change the slightly farty exhaust).

Secondly, could another fault destroy lambda sensors. I've changed it. A garage then changed it later and then a second garage said the first had used the wrong sort (titanium) and changed it again.

Reply to
Periproct

A leaking exhaust can be enough to throw emissions off. Easiest way to find out is a tin of GunGum.

But given the age of motor, and the symptoms, it is likely to be something else. But that something else, could take a bit of diagnosing.

Reply to
M Cuthill

I put the old Lambda sensor back on & measurements where OK

So back to the Stealers to get a replacement Lambda & they want me to pay them to diag the car themselves before refunding the first faulty Lambda??

I've bought another one & everything is OK, Cheaper than paying for an hours labour

Reply to
A C

Don't I know it. I've changed so much by guess work to start. Now I've bought a scope and been looking at the waveforms from some of the sensors. Using an HT pickup I found I seemed to be missing a spark every few turns of the engine. Changin the coil made quite a big difference to the running of the car but I haven't got the scope back on it since.

Found some really weird stuff like a near perfect sine wave from the plug lead sensor. Don't understand that one. And what looked like a load of mush from the crankshaft sensor. Changed it and no difference to the running at all.

I had considered the GunGum option but I think the leak is right at the front of the cat so the heat shield is going to have to come off so I might as well have the whole lot off and see if it is weldable.

Reply to
Periproct

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