[robwright]

Hi guys, I joined Vortex a very long time ago when i used to restore classic (70's) Beetles. This year i bought the wife a 2001 1.6 petrol "new" Beetle, and its brought nothing but joy for her (misery and pain for me lol) and the last problem in my long list of things I need to close out is a running issue with the IAT Inlet Air Temp sensor.

EDIT - I should also add, the car struggles to start sometimes, and runs rough until its warmed up at which point it drives beautifully. It does however, seem to be using a lot of fuel!

Essentially at startup the OBD reports a P0113 fault, and when monitored shows a constant air temp of -40deg C.
Air flow fluctuates nicely with revs - around 2g/sec at idle.

Work done so far:-

• XC MAF with 'good' 2nd hand spare
• tested fuses 43, 163 - OK
• Can't find a wiring schematic for 4-wire Bosch MAF but, Pin 3 gives 12V (13.8V actual when running)
• Can't find a 5V feed on the MAF connector.

My gut feel is there is either an issue with Fuel Pump 409 Relay, or an ECU issue where i should be getting a 5V signal feed.

Am i barking up the wrong tree, or is there something else i should be checking out? All advice / guidance / mental health support welcome!

Thanks
Rob

 

[VW Beetle]

Hey, I had the same problem with my Beetle recently. It was caused by several faulty MAF sensors. How do you know your second hand sensor is good? I ordered several sensors online and they all had a faulty IAT sensor. I also tried one from the junkyard. The one I bought from a local auto parts store finally worked.

My advice is to try out at least ten sensors to make sure the problem is not caused by a faulty sensor. Just return them if they don't work. Don't use any used parts.

 

[billymade]

I believe, on the 1.6L; the oem for VW is Hitachi, on the MAF sensor.

 

[Darepoole]

Here's two links to what I found for Bosch 4 wire maf wiring diagrams. Link1, link2. Hope this helps

 

[robwright]

Hey, I had the same problem with my Beetle recently. It was caused by several faulty MAF sensors. How do you know your second hand sensor is good? I ordered several sensors online and they all had a faulty IAT sensor. I also tried one from the junkyard. The one I bought from a local auto parts store finally worked.

My advice is to try out at least ten sensors to make sure the problem is not caused by a faulty sensor. Just return them if they don't work. Don't use any used parts.

Thanks for the info - its not that easy in the UK, no parts stores will allow you to return electrical components if you've tried them! Did you go or an OEM one in the end?

 

[robwright]

I believe, on the 1.6L; the oem for VW is Hitachi, on the MAF sensor.

Yeah it seems to be part of the MAF sensor, have tried replacing and cleaning but still showing as -40deg C

Do you think this would be a voltage issue? I've ordered some wre piercing probes to try and test supply voltages at the sensor wiring.From initial tests, i dont think im getting the +5VDC signal voltage to the MAF, but need the piercing probes to test the MAF under load.

 

[robwright]

Here's two links to what I found for Bosch 4 wire maf wiring diagrams. Link1, link2. Hope this helps

Hey thanks for this info - i'm going to be getting stuck into it again tomorrow - weather permitting!

Don't suppose you have a wiring diagram showing supply from the Fuel Pump Relay to the MAF also do you? I really need a full set of wiring diagrams for this car, but can't find them online!

Thanks for the help!

 

[Darepoole]

Hey thanks for this info - i'm going to be getting stuck into it again tomorrow - weather permitting!

Don't suppose you have a wiring diagram showing supply from the Fuel Pump Relay to the MAF also do you? I really need a full set of wiring diagrams for this car, but can't find them online!

Thanks for the help!

I don't unfortunately, I can look around though

 

[billymade]

Seeing how you have a UK spec vehicle; you could sign up for the online access of eRWin or the UK Haynes site, will allow access online or you could buy the paper repair manual. VW's factory wiring diagrams; can be a bit confusing to use and so, the Haynes manuals, use simplified redrawn diagrams and maybe a easier to use wiring diagram.

Volkswagen Workshop Manuals from £19.00

A Haynes manual makes it EASY to service and repair your Volkswagen. Online, digital, PDF and print manuals for all popular models

haynes.com

Volkswagen AG erWin Online

erwin.volkswagen.de

 

[VW Beetle]

Thanks for the info - its not that easy in the UK, no parts stores will allow you to return electrical components if you've tried them! Did you go or an OEM one in the end?

That is one of the really pleasant things about the US - one can nearly return any product, no questions asked, very straight forward.
I ordered one non-OEM and two from Bosch online - all of them had the IAT issue. The Bosch sensor I bought at a local auto parts store worked finally.

You can't return faulty or broken products in the UK? If you buy a MAF sensor at a parts store, install it in their parking lot and it is not showing a resonable IAT, I woukd expect that you can return it immediately to them or at least exchange it for another one.

I can just advise you to save all the wiring testing action for after making sure that not the MAF+IAT sensor is causing the issues. I am pretty sure you can save yourself all that work.

 

[robwright]

SOLVED!!!

OK - so this is gonna be a bit wordy but ill try to keep it brief:-

• Tested the MAF IAT sensor across its terminals and got the correct range for resistance - no issues found
• Tested the voltages at the MAF connectors (Pins 1 & 3 for the 1.6l engine) - no issues found
• Tried an aftermarket MAF and still got same results - same concern (IAT reading -40deg C)
• Checked all vehicle grounding points - no issues found
• Checked ECM connections - no issues found

• STRIPPED BACK WIRING FROM SENSOR CONNECTOR TO ECM AND FOUND BREAK IN HARNESS
• Repaired broken wiring and rebuilt everything back together and tested - Car started straight away, and read 8~9degrees C for inlet air temp. This continued rising as the car warmed up!

Over the next couple weeks I will monitor fuel consumption and starting, and update if there are any new developments.

I've attached some images of some items that may be of use for people with similar issues going fowards

Thanks to all who helped, advised - got there in the end!

 

[billymade]

Solid troubleshooting and diagnosis! Always, expect wiring issues; the Mark IV era Volkswagens, are notorius; for damaged and deteriorating wiring harnesses, plugs, wiring, etc. Nice work and thanks for sharing the service manual info and your final, resolution, to your problem! Cheers!