2.0 JTS fault code interpretation
Hi All. I'm still trying to sor out my wife's 156 JTS 2.0. It's engine management light is on and although I originally had P1151 (Lambda plausibility Bank 2 pre-cat) and P0154 (Lambda bank 2 pre-cat slow response), I now have P1151 and P1131 (Lambda plausibility Bank2 pre-cat AND Bank 1 Pre-cat).
Now to loose one lambda sensor might be considered unfortunate, but to loose two, starts to look like carelessnes!
Can anyone think of any other reasons for the fault besides both Lamda sensors having gone down?
Using the "Monitor" function of Alfadiag, with the engine hot and idling, I'm getting Lambda voltages of about 3V on each of them (i.e. off the scale, which only goes from 0 to 1). The "Measured Lambda value" for Bank 1 pre-cat is between 2 and 4 (on a scale of 0-16) and it's between 1.5 and 1.8 and Bank 1 (on the same scale). Blipping the throttle causes both traces to show small spikes, although they aren't as pronounced on Bank 2.
When I disconnect the MAF, the car seems to drive exactly the same as when it's connected. No difference in power. The Lambda readings don't look significantly different without the MAF connected, which surprises me! With the MAF connected (again at idle) it quotes the air consumption as 12.5kg/h and the inlet air temperature at 45 degrees. The mass flow rate goes up and the temperature goes down when I blip the throttle - which I guess is reasonable.
Idle seems slightly rougher than normal.
There are other Lambda sensor outputs to log further down the menu, These all resut in the message "open loop" (i.e. Lambda pre-cat Bank1 open loop, Bank 2 open loop, Lambda post-cat Bank 1 open loop and Bank 2 open loop). I would have thought they'd all be closed-loop at idle when warm?
Finally, if I clear all the fault codes, the light goes out and the car can be driven for about 10-15 miles before it comes back on again.
Can anyone tell me:
1. What sort of "Measured Lambda Value" should I be seeing on the pre-cat sensors at hot idle? (I guess about 1 would be good)?
2. Does a measured value of 2 on a scale from 0-16 mean it's running rich or weak? (I'm guessing rich)?
3. What sort of voltage should I be seeing from the pre-cat sensors under the same condition? (I'm guessing that if the scale only goes from 0-1, I shouldn't be seeing values of about 3)!
4. Can a MAF give credible readings such as mine but still be faulty?
5. Is it common for both pre-cat lambda sensors to fail at the same time?
6. Is there anything else that could cause them to read out of range?