OBD codes - 02S and EVAP not ready

[Wing Commander]

I am after some help in diagnosing the codes from my Saab 9000.

I have just bought a U480 OBD scanner/reader and have plugged it in as per the instructions, ie the engine is off but ignition is on. I don't get any DTC codes come up but I get two I/M codes. These are "02S not ready" and "EVAP not ready".

What does this mean? The handbook says that "not ready" means that the monitor has not finished its diagnostic testing, but this seems odd as the scan has completed.

Would it be caused by the car being cold each time I test it? Or is it because the 02 sensor isn't currently in use (because the engine is off) so it gives a weird result?

Any guidance would be great - thanks!

[anonymous-user]

"not ready" means that the items to be diagnosed are not in a state that is suitable for that diagnosis to take place:

For the O2 sensor, it must be hot to be checked, this obviously requires the engine to be running!

For the Evap, the system must be able to pull a vacuum on the fuel tank and check the purge valve flow rate, again, requires a running engine (and probably a steady speed cruise at approx 40-50mph at a steady throttle) to complete those monitors.


So the O2 monitor should complete after a period of engine idling after it is warmed up (coolant temp normal) and the Evap monitor should complete after a steady drive at 40mph with a warm engine

[Wing Commander]

Thanks! That is really useful Confirmed my initial thoughts but this is a new, black art to me!

I presume you mean I run the car at 40ish with a warm engine, then pull over, turn engine off and then test?

It says I shouldn't use the reader with the engine running - hence my thinking.

Thanks again!

[Wing Commander]

Me again - I took the car out for a 30 min run so the car was thoroughly warmed up. The run was between 40 and 60 mph for at least 10-15 minutes so that should have given the car a good amount of opportunity to clear both the 02s and evap "not ready" codes.

I cleared the codes before I set off, and rescanned when I got home. Unfortunately they are still on there.

Could this mean the 02 sensor is on the way out??

Thanks

[anonymous-user]

I am assuming that you are not doing "intrusive" tests with your code reader. i.e. you are not asking the code reader to tell the ecu to do a test, but simply reading the results of the std EOBD tests that the ecu runs all the time.

In this case then using the tester with a running engine is not an issue (active tests could be, because for example you wouldnt want to override say a throttle or injector command whilst the engine is running

The O2 not ready code will be present at all times the system cannot monitor the O2 sensors conditon (because the EOBD stds mandate that the o2 sensor must have continuous monitoring (except during warmup) If the sensor had failed i would expect to see a "O2 sensor no or slow response" code set.

If you code reader can read the std EOBD PID's then you should be able to see a "live" exhaust sensor voltage value, which should be continously switching from approx 0.2 to 0.8 volts (ish) at idle (with a 0.5 to 2hz period)

The "EVAP" tests are much harder to get to run, as you typically need to get through the following entry conditions:

1) fuel level between 15 and 85%
2) road speed between 30 and 60mph
3) steady throttle value below 50%
4) no "rough road" input from the wheel speed or crank sensor (to avoid fuel "slosh" etc)
5) fully warm engine


But again, even if the monitor hasnt run the last trip, if it had failed you would expect to get some "purge valve failed" or "fuel tank leak" codes! (simple test, drive car for 15mins, stop, keyoff, open fuel filler cap asap, you should hear a "hsss" as air gets back into tank. (system pulls vacuum on tank to capture fuel vapour during running) (also, if you find the purge valve, typically underbonnet somewhere on the inner wing area, with the engine at idle you should hear/feel the valve "ticking" as it operates)

[Wing Commander]

Thanks once again

I assume it is a non-intrusive test as its just a boggo reader from internet land (U480)

I will run it up tomorrow and see if I can get a different result with the engine running.

[Wing Commander]

Haven't had a chance to give the car a test whilst on the run but did do a test after the car has warmed up. Still had the same results for both the 02s and EVAP.

Arse

[anonymous-user]

Let me just re-iterate to avoid any confusion:

Those codes do NOT mean anything is wrong with your car, they mean that the car has not had a chance on the last "trip" to check if they ARE ok.



(now, the things they are monitoring might be buggered, but i suspect it's unlikely)