Lambda Woes

Steve Medlock

Steve Medlock

Zorg Guru (II)
British Zeds
Joined
May 11, 2016
Points
105
Location
Tenterden, Kent
Model of Z
2.8 Roadster
Vicky has been running rough recently particularly on start up. At MOT on Wednesday, the tester and 3 assistants really struggled to find any sweet spot where the Lambda value would come below the limit. They were brilliant though and got me a pass. I've had to re-install my INPA and am having a heck of a time getting it to run at all - constant error messages!
I did manage to get this from the error memory though:

455335014_10229972813879264_4114941754942524549_n.webp


The technicians said Lambda sensor mate - but is it?

Steve.
 
202 is a post cat bank 1 fault code.

With a hot engine, monitor the sensors voltage.

Reading the Post-Cat O2 sensor voltage:

  • Cat's in good condition have Post-Cat O2 voltages above 0.5V. When at steady highway cruise, there may be the odd momentary dips.
  • If O2 sensors are switching between 0.1 and 0.8V, this shows that the Cat’s are not able to treat the exhaust and indicates struggling Cat's. They are following the pre-cat O2 sensors. This is the same for either narrow band or wide band Pre-Cat O2 sensors. Expect to start seeing P0420 and P0430 Cat efficiency below threshold codes.
  • If O2 sensors are flat lined somewhere below 0.5V, you have one of these problems:
    • Faulty post-cat sensors
    • Blocked Cats. Check fuel trims, they are likely double-digit rich at cruise RPM’s. Do a before the Cat’s exhaust pressure test.
    • Fuel mixture problems that are so lean that it is being reflected in the post-cat O2 sensor signals
 
I had issues with them on my MOT, a new one resolved, they are quite cheap to buy.
 
As indicated previously, the post cat O2 sensor is primarily used for diagnosing the catalytic converter. It only has a very small influence on fuel trim so shouldn’t be the root cause of poor running or emissions performance in of itself. I think you need to concentrate on upstream issues.
 
NZ00Z3 said:
202 is a post cat bank 1 fault code.

With a hot engine, monitor the sensors voltage.

Reading the Post-Cat O2 sensor voltage:

  • Cat's in good condition have Post-Cat O2 voltages above 0.5V. When at steady highway cruise, there may be the odd momentary dips.
  • If O2 sensors are switching between 0.1 and 0.8V, this shows that the Cat’s are not able to treat the exhaust and indicates struggling Cat's. They are following the pre-cat O2 sensors. This is the same for either narrow band or wide band Pre-Cat O2 sensors. Expect to start seeing P0420 and P0430 Cat efficiency below threshold codes.
  • If O2 sensors are flat lined somewhere below 0.5V, you have one of these problems:
    • Faulty post-cat sensors
    • Blocked Cats. Check fuel trims, they are likely double-digit rich at cruise RPM’s. Do a before the Cat’s exhaust pressure test.
    • Fuel mixture problems that are so lean that it is being reflected in the post-cat O2 sensor signals
Click to expand...
Are you sure this 202 code is the post cat sensor? The German text refers to control limit which is more applicable to the pre cat sensor.
The answer I gave earlier only applies to the post cat sensor, the pre-cat sensor is the primary fuel control sensor and if that’s faulty, then emissions will be shot and it’ll probably run rough too.
Here’s some better advice: ditch INPA, Creator and all other ancient junk that doesn’t display DTCs in the industry standard format - powertrain codes should be displayed Pxxxx.
Oxygen sensor codes, typically P0130, P0135, etc. you’ll stand a much better chance of successful diagnosis with good data.
This stuff has been mandated for over 20 years. Half decent readers are given away free as phone apps,

rant over.
 
It could be, who’d know? Too easy to create errors with a decode list like that. Much better to get the real answer directly with a tool that displays the stored data correctly.
Also, I see that the OP has a ‘98 MY vehicle. UK (and EU) legislation didn’t mandate catalyst monitoring at that time so it’s more than likely that there is no post cat O2 sensor fitted. A good tool will also show this information.
 
OR, a quick look under the car will reveal if there is a "post cat" sensor fitted?

Tony.
 
t-tony said:
OR, a quick look under the car will reveal if there is a "post cat" sensor fitted?

Tony.
Click to expand...
Always good to use all available diagnostic equipment, the distinction here being:
It's not fitted and not meant to be fitted vs It's not fitted hence indicating a fault.
 
Last edited:
Thanks for the responses chaps. I've had to work on my daily driver car unfortunately so haven't been able to get back to this.

A couple of things:

I only have one oxygen sensor located pre-cat
Bentley manual says 202 is fuel trim bank 1

I do have INPA working on the laptop at last so I'll see tomorrow if anything jumps out as abnormal.

Regarding ditching INPA - is there an alternative diagnostic for OBD1 systems?

Steve.
 
Re 202, German isn't my language but Lanbdareglergrenze appears to mean something like 'lambda regulation limit' which I suppose is fuel trim. I do get impression that its over fuelling - low mpg and much more exhaust popping and banging than normal.
 
Over fuelling usually comes back to unmetered air in the induction.

Tony.
 
Ditch INPA for OBDII systems. Your engine controller is OBDII compliant. As there's no alternative, use it for what ever OBDI systems you need to diagnose and best of luck with that!!
Fuel trim bank 1 makes more sense. If the fuel trim is maxed out, look for air leaks.
This thread explains exactly why CARB were so insistent on making diagnostics a regulated standard.
It looks like you don't need a new O2 sensor, good luck with the ongoing investigation.
 
Hi Steve i see your zed is a 98 2.8.
Which engine is in it
Is it an earlier single vanos engine or a later twin vanos tu engine.
If its the later tu unit it has 4 lambda sensors 2 pre cats 2post cats.
 
Stevo7682 said:
Hi Steve i see your zed is a 98 2.8.
Which engine is in it
Is it an earlier single vanos engine or a later twin vanos tu engine.
If its the later tu unit it has 4 lambda sensors 2 pre cats 2post cats.
Click to expand...
Hi Stevo,

Its M52b28/single vanos/single sensor
 
Steve Medlock said:
Hi Stevo,

Its M52b28/single vanos/single sensor
Click to expand...
@Scooblitz Stevie was having various issues with emissions and other stuff diag showing lambda sensor fault
One fairly expensive Bosch direct fit lambda later and his zed has had no further running or emissions issues since.
Stephen.
 
OK I'm feeling really dim! I should have looked more carefully as there was a split in the idle control hose right at the bottom of the jubilee clip. It was obvious (?) when the engine was running but wasn't so obvious when it wasn't running. Surprised to find I didn't have a spare so I've had to order one. You were spot on with that one Tony!
 
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