just replaced my maf sensor for a brand spanky new one reset the ecu stc done everything correctly and by the book but its still saying theres a problem with the maf sensor circuit
what other faults could there be ????????????

 

You might not have reset the ECU properly. What procedure are you using to reset the ECU?

 

tryed the plug method a few times with the connectors under the dash but that didnt work so disconnected the battery for 48 hours i know the reset worked because i also had to change the knock sensor and its cleared that fault

 

In which case dodgy connector or short somewhere. Bit harder to diagnose without taking it to a subaru specialist.

 

so by that then should i track the wires from the maf back and see where that leads me ??

 

You should firstly get your new MAF checked out to make sure it is working 100%. I realise it's new but it wouldn't be the first time something new has been purchased faulty. You should also think about checking out the old one to make sure you haven't bought a new MAF in error.

Do you know anyone near you that you could swap MAF's with just to check if both your MAF's are working or not?

You need to get hold of a manual and read the schematics and fault finding section to check what the inputs/outputs at the connector should be before going to the trouble of tracing wires looking for a break or short which may not reveal itself upon visual inspection. It may end up being quicker just to reference the manual.

Can't say any more really apart from using a set process of elimination to track down the fault DIY other than going to a Subaru specialist and spending money.

 

In addition to Scoobiewrx's advice, can you tell us exactly what you did, and exactly what you mean by "didn't work"?

 

on scoobypedia there is a guide as to reseting the ecu and also the fault codes using the green connectors and the black connectors this didnt reset my ecu and i followed the guide to the letter so i disconnected the battery for 48 hours and then reconnected it, instantly it cleared the knock sensor fault as i had just fitted a new one but still shows maf sensor curcuit code

 

I've not looked on ScoobyPedia but did this involve connectiing the appropriate connectors under the dash, pressing your accelerator pedal down, switching the ignition on and keeping the pedal down for 10secs, then starting the engine and driving around above a certain speed waiting for the mil light to flash steadily??

 

If that's what he read, the Scoobypedia article is a little overcomplicated. There's no need to do anything unusual with the accelerator pedal prior to switching on, just start it and drive.

Dan, for want of flogging a dead horse, can you tell us exactly what you mean by "this didnt reset my ecu"? If you connect the green and black plugs, start the engine and drive the car, one or two things will eventually happen. Either the Check Engine light will flash a continuous on/off/on/off sequence, or it will flash out numeric error codes in the same manner as you've seen with the black plugs on their own.

Which of the above happened, or was it something else again?

 

after driving it the error codes for both the knock sensor were both still flashing this method did nothing except waste petrol and test my patience loljust so i was sure i wasnt being a mong i printed the oagfe off and followed it exactly still no joy still flashing the error code thats when i disconnected the battery and left it for 48 hours then reconnected it where i found the CEL was still on so i did another diog check and it had cleared the knock sensor fault but the maf sensor curuit code was still there

 

Apart from disconnecting your battery the reset method if done properly resets the ECU and clears old error codes but clearly if there are problems you will see error codes no matter how many times you reset.

They won't go away until they are fixed so if after driving with your connectors still hooked up down below you still got a knock sensor code then you have a problem with the knock sensor, and the same for the MAF. Go through the process of elimination as has already been explained to you or go and see a Subaru specialist.

The problem with cars as they start to get old is they can and do develop electrical issues. Your car is 14yrs old so it's reasonable to expect either mechanical or electrical problems at some stage.

 

i think the whole point of my original post has been missed now lol
its clear i have done a reset and all the other good stuff to go along with it the problem is i want to find out if there are any other common problems that could cause the maf fault in the system other than the actual maf as i have a brand new one if there are none then i will see a specialist.
im trying to use this route first as im based in germany with the army and the germans are quite short of subarus and suabaru garages

 

The point of your original post is that you have a recurring MAF sensor error code coming up on your car and you have changed the MAF for a new one. Unless you can check both your MAF's to make sure they are definateily working you have to assume that the new one works. Therefore you may well have an electrical issue in which case either go to a Subaru specialist or as has been already pointed out to you, get a manual and do some DIY fault finding.

It's unfortunate that you're in Germany and there are a lack of specialists. I've just had a look online and done a search. Suffice to say subaru specialists in Germany are as rare as pots of gold at the end of a rainbow, and i cannot quickly come up with a name/number for you so it looks like you're going to swiftly become a subaru electrical specialist whether you like it or not. Being in the Army....Can't you get REME's to have a look

 

Not at all, I was waiting for you to say what the actual result of your ECU reset attempts was before I could work out what was going on.

As Scoobie has already said, you are carrying out the reset procedure correctly, but the reason it is not working is because you have, by the sound of things, two current and constant faults. The procedure will only give you the all clear if everything is, as it sounds, all clear.

Yes, MAF overvoltage/undervoltage will do it - so a short or open circuit in the wiring loom for example. As you've bought a new sensor it would be logical to assume that it's working so in practice, in the absence of a local specialist, you'll have to trace back the signal wire for the MAF sensor from the plug in the engine bay to its counterpart in the ECU. Check for electrical continuity and also make sure it doesn't short to ground (or any other wires in the loom).

Also you say that your reset procedure is pinging back the knock sensor circuit error too. Again you'll have to follow the signal wire through from engine to ECU and check continuity/shorting. If it all checks out, try a new sensor. Afraid I don't know off the top of my head what the typical impedances of the phase 1 sensors is but if you test it, you should see a consistent resistance (probably in the hundreds of kilohm range) between the metal base of the sensor and the signal pin in the wire. If it's open circuit, it's junk.

 

If you need a downloadable workshop manual just shout as there are plenty about.

 

no the knock sensor is fine now no problems with that..

could do with some wiring guides as ive looked and cant seem to find any if there are any around ??

 

ok i stripped all the tape and crap off the wires this morning and found something rather confusing at first glance it appears that the green wire has just been pushed into the grey wire but i cut the rubber in various places up the wire and the green wire runs through the centre of the grey one all the way along.
so what does the grey wire do should this be connected somewhere ?????

 

heres the pics to go with my previous post

 

It looks like some kind of shielding. Shielding is noramly used as a ground so i cannot advise there. I'll pm you a link to a workshop manual. Hopefully the link still works.

 

and the problems continue the car has forgotten the maf sensor now lol
it starts and runs with the maf unplugged
can this be fixed easily ????

 

The problem with not having a MAF is that your ECU now doesn't know how much to fuel and won't be running that well. I think it defaults to safe (rich) fueling so hopefully no chance of detting if you drive carefully.

I don't know if V.1&2 ECU's do a similar thing to newage denso ECU's in that they run a limp mode that doesn't rely on the MAF, running almost like a speed density mode. If the MAF is causing that much of an issue you can have your ECU remapped to run MAFLESS using an ESL duaghterboard which does away with the MAF altogether.

In the absence of another solution you're going to have to get down to the bottom of your wiring issue otherwise this is going to be a long term illness.

 

In your pic the sheilding on the green wire is fine BUT the red tape is not OME looking along the loom the tape looks to have been re-done even the black (maybe wrong from just looking at a pic) but worth checking also as others have already said try to check you replacement maf in another car to confirm its good as new ones have been faulty in the past!!!

 

sy. yeah i re did all the tape as the original stuff that was on was tatty

scoobie. the drama im now facing is i want to get it back to the uk to get it into a scooby specialist but driving it doesnt seem like a safe option from germany back to the uk when its running like this ARGHHH lol i am determined to get this sorted though

 

If you drive off boost and as granny like as you can it will get back from germany. You just have to take it very easy. The only other way is if you have european car recovery cover that will get your car back to the UK.

 

As has been said the coaxial shield on the MAF signal wire is perfectly normal and is there to protect the airflow signal (and the ECU as a whole) from interference. It should be terminated in the loom next to the ECU to a common sensor ground, and from there connect to the ECU itself - not sure which pin this would be on an early car, but the manual will tell you.

Scoobie - the later classics look up a 3D map with throttle position and RPM as indexes and produce an approximate value for the MAF input used to feed the load/fuel/etc tables when error 23 is set. However whether the earlier ones do the same I couldn't comment, and on the later cars doesn't work much above idle speeds anyway.

Dan: Have you yet checked the electrical continuity of the MAF signal line from the connector in the engine bay through to the ECU plug?

 

thats just a bit of electritians jargon to me mate hahaha maybe in dummies terms i would understand lol

 

Splitpin: Denso ECU's do a very similar thing with MAP v RPM using base load compensations to adjust fuelling etc...

Dan: Have you downloaded the workshop manual from a link i PM'd you? That will show you the ECU pin outs. You can link up which pins on the MAF connector correspond to pins on the ECU. Checking for continuity just means that you're checking with a multimeter to see if there is a break in the wire somewhere. If there is a break you won't get a reading or buzzer sound, depends on which multimeter you use, conversely if there isn't a break you will get a reading/buzzer sound.

 

You must be able to find a mech/spark somewhere who knows this stuff man, that's what the Army is for.

Simple language: You need to make sure that the mass air flow voltage is actually getting all the way through from that green/silver fleck wire in your engine bay through to its opposite end at the ECU without shorting out against anything else. If the wire's broken somewhere then the signal from your MAF sensor won't get through to where it needs to be.

Electrician will use a continuity or resistance meter to check that all is good. If push comes to shove you can test it with some wire, a battery and a lightbulb but if you can find someone round by you who knows some auto electrics, that'd make things a lot easier.

Also heed Sy's advice earlier. Even though you've bought a new sensor, they can, very occasionally, be duff in the box. If you have any way of putting that sensor in another car to cross-check it, that would be well worth doing.