What you need is a bit of electronic gadgetry to log the voltage output of the sensor as tfb mentions.

Gives me an idea for a project sometime, not sure if you're an electronics person or not but an Arduino with SD-card shield would probably do the job nicely, set it to log two voltage sense inputs using a voltage/resistive divider on each (allow up to 12v to be safe I'd say), that way you can take your reference voltage going into the MAFS and then it's output/return, log it's output every 30 seconds (or smaller delay, depending on the sample period needed) say and give it a whirl.

Not exactly a quick fix/check but it's a potential way of doing the same on a budget.

 

You can pick up USB scopes on ebay from about £50 upwards, though a Arduino or PI gives you lots of other things you can do. Sample rate would need to be at least 50ms, given that a fault is logged if the reference exceeds the parameters for 100ms.

Spending £50-80 on a scope for just one fault is hard to justify though.

Regards
Ricahrd

 

Thanks guys I'll think this over with a strong drink. As to £50+ Christmas is looming and I'm on a budget. But if the rain stops, eventually, I/we'll get back on it. But again thank god its still useable.