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I have a Bosch 0280 212 016 Air Mass Meter on a Volvo 240. Does anyone know how to test this particular unit pin 1 and 2 are common. 2 to 3 measeures 3.2 ohms pins 1 to 4 measures 23.12K and 1 to 5 measures 21.22K Pin 6 O/C. Any help welcome. Thanks Peter
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hi peter,
i have a nissan terrano with a bosch mafm on it and the feed back signal to the ecm is from pin 5 on mine its a d.c voltage of engine stopped:aprox 1v, at idle:1.6-2.0v and at 4,000 rpm approx 4v .also pin 2 on mine is 12v battery voltage and pin 4 is sensor power supply 5v,my cd workshop manual says to check for these voltages at the return point of the ecm you would need to check you manual for this one.also you need to check the power at different point of the harness assemblies(mine has two of the ecm to harness then out through the dash to the sensor harness)manual states if no signal at ecm terminal then either maf sensor no good or harness shorted.it also tells you to loosen and re-tighten all af the engine grounds.as for resistance it does not metion this but obviously it will have one as its an element of some sort.
hope this helps
regards
andy
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Peter,
If the air flow meter is a hot wire type, the hot wire element can be checked by watching through the air flow meter after you shut down the hot engine. There is a cleaning cycle where the hot wire is briefly lit up like a bulb filament.
I don't know which pins should be giving which voltages for your car, but I do know that it is very unusual for these units to fail completely, but I have known them fail partially, which is much more difficult to diagnose properly.
As an example, I dealt with one very troublesome case on a Calibra Turbo. Everything checked out OK against the checking procedures, but it still ran like a donkey, spluttering and refusing to rev up. This car had already been in the garage where I used to work for over a month before I was asked to have a look. After checking the whole system out, and finding nothing wrong when compared to the spec., out of desperation, I blocked about half of the input to the mass air flow meter with my hand, and it began to run OK. So, although the air flow meter did check out against the published figures, a new one cured the fault!
Sorry if that's not particularly helpful for your problem, but that is my experience with these things!
Number_Cruncher
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I have always 'tested' mafs by swapping for a known good unit.
I think Number_Cruncher is right, they are a pain to test and commonly semi-fail giving problems.
On the plus side, lots of mafs have exactly the same probe but different bodies. Is that part number off the body or the probe ?
They are much cheaper (1/3rd price in my experience) from a motor factor than volvo.
Bosch also do what they call 'reconditioned' mafs - no idea what this means but the one I bought seemed to be brand new in every way.
Pierburg also do a replacement probe for the bosch hot wire mafs which uses a solid probe. Seems to give better fuel economy, worse pickup/response, as you might expect.
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Thanks for writing that Mark, it is good to find out that others also find the diagnosis of these things a bit tricky.
Number_Cruncher
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Update I managed to speak at great lenght tot the head Mech at a main Volvo dealer and he gave me the figures staraight out of the book. Pins 1 and 2 are common and groundedi staright to ground and 2 via the ecu, pins 2 to 3 2.5 to 4 ohms, ignition on 1.4V at pin 3 and 2.3 at idle then rising with rpm to 4 at 4k. pin 4 on this unit is refered to at an information signal going to the ECU although my manual suggests it is the burn off element. Its resistance is 23.12K so may be a lh 2.4 does not use burn-off. However my AMM checks out OK but car still rough. Went for a good run and it improved, no reported cosed but I tapped into the Lamdda ( Scope )signal and it is only crossing every few seconds. The car when hot is idling at about 1050 rpm. Now if toy crack the trottle open the voltage immediately drops to 0.1V and that is where it stays until you go back to idel then eventually it will cycle but very slowly and erratically. Time for a new Lambda I think. I can only summise that the 20 miles it was driven with no in tank has starved the system and burnt the end off the sensor which has done 97K. Any opinions welcome. All this and still ne error codes. Thanks Guys. Regards
Peter
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More interesting tests. Engine cold Lambda heater resistance 12.2 ohms, all scoped up to the Lambda probe. Turn on open loop mode voltage reads 0.6V . 2 minutes later it starts to cycle slowly and erratically 0.15 to 0.9V Touch throttle and instantly drops to 0.15V and 10 seconds later starts to cycle again. Rev the engine and the level drops and on the overrun the level rises initially then falls to 0.15 and starts to cycle 15 seconds later. Hold the engine at 2500 rpm for 30 seconds solid0.12 volts back to idle 10 seconds later starts to cycle slowly again. When it is in cycle mode it averages 0.55V. So propane test gas on and a few second in and the voltage rises to 0.9v and engine rpm lists slightly gas off level slowly falls and 20 seconds later the sensor cycles again.
Engine running smoothly but at 1100 rpm instead of normal 900 ish. Engine doesn?t miss but clearly no idle control. I?ve checked all over for air leaks, vacuum pipes, leads feed and everything else. I am in the fortunate position of being able to swap to a spare ECU but exactly the same. Any ideas where to look next would be most welcome as I am bang my head on the garage wall here. Regards Peter
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