240 General: Lambda sond errors 322 & 121.

[gnnmartin]

We have a 1990 240 Volvo estate. From time to time the Lambda Sond warning lights up, and the code given is 322 together with 121. Code 322 translates as ‘Air mass meter hot wire burn-off not functioning’ and 121 translates as ‘Fault in signal for air mass meter’.

The car usually runs a bit roughly before the Lamda sond warning light comes on, and it continues to run roughly until the code is read and cancelled. When the car is running roughly, it is most noticeable when pulling away at low speed, and it tends to smell of unburnt fuel (so my wife tells me, my sense of smell is not very acute).

Usually, when the code is read and cancelled the lambda sond warning stays off and the car runs normally. This leads me to suppose that when the error has been posted the ignition system assumes it cannot rely on the air mass meter signal so it uses a fall-back algorithm, and it continues to use the fall back algorithm until the code is read and cancelled. Is that correct?

Sometimes the first read out and cancellation of the warning does not cure the problem, and the lambda sond warning light turns on again within a few miles. Trying again after a few days & miles usually clears the problem.

Any idea how I get the hot wire burn-off to work reliably? The air mass meter is rather an expensive item, and I get the impression that the problem is not in the meter itself.

[DW42]

You can try disconnecting and reconnecting the AMM connector in case it's a bad connection. The AMM wire is quite delicate, but you could try to clean it with a throttle body/intake cleaner. But it sounds like you need to bite the bullet and buy a new or known working used AMM. One reason for AMM failure is failure of the air box thermostat. This can mean that the car is always drawing air to the intake via that big silver accordion hose that originates near the exhaust manifold. Constant hot air will kill an AMM eventually. Unless you live in northern Sweden or Alaska or somewhere like that, you should remove the air box thermostat and block up the hole. You don't need this system for quick warm-ups in the UK.

[gnnmartin]

I'll take a bit of time digesting that, and will probably come back for more information, if I may, please. In the mean time, thank you.

[CosmicBike]

Unplug the Mass Airflow Sensor and see how it runs. I may well smooth out a bit, but will run very rich and not be too happy. I had the same and picked up a MAF from a 740 on Ebay which solved my problem, you can use a MAF from a 240, 740 or 940 so options are there on the used market.

As @DW42 has advised, the hot air intake is really not needed in the UK. I removed the hose, blocked the inlet and removed the hot/cold thermostat operated flap. Mine warm plenty fast enough in the Winter.

[gnnmartin]

Thanks. Since I last posted the car came to a complete stop after running roughly for 2 miles and lighting the Lambda Sond warning. My wife was driving it (she is the main user), and she found the code was 133 (Throttle switch idle contacts shorted or out of adjustment). She cleared the code and the car ran sweetly home. Are the errors reported by the Lambda Sond reliable & consistent, or is it a 'best guess'? Do you remember when you had problems, did the LS ever give an error code other than 322 & 121?

There is a local garage of the old school, familiar with old cars, though not particularly Volvo. I talked to him & he suggested changing the oxygen sensor (I hope I've remembered that correctly!), since it is cheap and he think it might help. So I'll go ahead with that while I search for an Mass Airflow Sensor and poke around under the bonnet to understand your recommendation about the hot air intake and the associated thermostat.

Thanks again.

[Clifford Pope]

Whenever I think I am beginning to understand how the Lambda-sond works something happens or I read something that makes me realise I don't understand it at all.
I used to think that the warning light - just that - a notification that an error had just triggered the light. That could have been a real and still-present error, or it could just have been a momentary error.
Either way, if the light stays on it indicates that a fault has been logged. But logging a fault does not mean it is still existent. It may or may not actually still exist, but the system needs reading and clearing anyway.

But now your experience shows that the mere act of clearing the code itself can clear the fault - your car wouldn't work until you had cleared the code, and then it ran perfectly. So now I realise I was incorrect in my understanding, and I don't know anything and can't help.

The only thing I can suggest is that perhaps the system has the power to reset itself, eg the AMM can operate in "limp home mode", not perfect but good enough to get home.
But perhaps it can only do that after the code has been cleared?

I did once have a 240 that ran on LPG. When on LPG it ignored the lambda system and always displayed the light. But on first switching to petrol - eg when starting up next time - it ran off-colour if I hadn't reset the code. I presume it needed a few seconds to re-adjust to petrol.

It seems to me you either need a proper diagnosis by a qualified expert with test equipment, or you experiment just by replacing the AMM and oxygen sensor and see what happens.
I would just repeat my old favourite, check all earths. There is the main earth hidden behind the battery, and the thin bit of plaited wire earthing the top of the engine at the cam cover.

[CosmicBike]

Originally Posted by Clifford Pope

Whenever I think I am beginning to understand how the Lambda-sond works something happens or I read something that makes me realise I don't understand it at all.

Glad it's not just me then, I knew I'd figured the issues with mine until I realised I hadn't!!

[gnnmartin]

Originally Posted by Clifford Pope

the AMM can operate in "limp home mode", not perfect but good enough to get home.

That is indeed the case. You can demonstrate this by disconnecting the AMM and the car still runs. The story I was told is that the data from the AMM helps optimise the running, but when the ignition system detects that the AMM data is unreliable it uses default data. The engine runs, but sub-optimally.

I guess that while an error code is logged the computer assumes the corresponding data is unreliable. In other words, the error may have gone but the computer continues to run with default data. Once the code is cleared, the car tries to use data from the erstwhile failing part. If the data is still bad, the lambda sond will again light and the code will be set again. If the underlying error has disappeared, all is sweetness.

Mark you, my post is a mixture of guesswork and hearsay and experience, no reliable design information!

I'm happy to say we drove about 40 miles today and the car behaved well.

[gnnmartin]

On advice from a local garage who does impress me, we've replaced the oxygen sensor, on the grounds that it is cheap and might be the problem. If things are still rough, we'll try getting a second hand air mass meter and removing the hot air intake as suggested by D42 and Cosmicbike above.

[Stephen Edwin]

Originally Posted by gnnmartin

On advice from a local garage who does impress me, we've replaced the oxygen sensor, on the grounds that it is cheap and might be the problem. If things are still rough, we'll try getting a second hand air mass meter and removing the hot air intake as suggested by D42 and Cosmicbike above.

Hello. Removing the hot air intake is long standing advice in the forum. Not to remedy a problem that has occurred, but to avoid a problem occurring. I recommend doing it whether things are still rough or not.

Stephen

.