1.6 petrol A4 bad starting, MAF sensor testing?


Registered User
Hi, sorry to bother you all for the third time with the same problem! I'm still having issues with my 1.6 petrol (engine code ALZ I'm pretty sure - coil pack instead of coil in plug cap).

My original post below suggested several things and I'm trying to work through them. I replaced the coolant temp sensor and am looking at the MAF sensor now. As it's a lot more expensive I'd rather be sure it's gone before replacing it.

It's a 4 pin type, and I got the following resistance readings (unplugged & pin numbers as written on the plug/harness) :

  • 1,2 - 3.7 K ohm
  • 1,3 - open circuit
  • 1,4 - 6.3 K ohm
  • 2,3 - open circuit
  • 2,4 - 2.6 K ohm
  • 3,4 - open circuit

So, it would appear that pin 3 is not connected to anything. There are 4 wires going into the plug. If the MAF just has simple resistance wires, then I found a problem, however, if there is electronics in it, these could be valid values in an inactive state. I understand there are 3 types of MAF, simple resistance, slow frequency out and high frequency out. The latter two must have electronics in them?

To experiment, I unplugged the connection the last few days, and the car is starting on the button now! It did throw a P0102 and PP0113 though. So, with the MAF connected, no errors and bad starting, disconnected, errors and good starting and running!

This post details the CTS replacement and has a video of the car trying to start, plus a pic of the engine (to confirm code)

Many thanks,


Registered User
99% sure its not resistance. It'll most likely be a Bosch HFM or hot wire in which case they have active electronics. Power, Ground, Ref and output. They do still fail though.
If it works better with the MAF unplugged then you can be fairly sure that is the issue. Always, Always, Always get the OEM manufacture for things like MAF, normally Bosch. (Or just genuine)
If you get any other brand you'll either be lucky and it work or you'll be chasing issues forever


Registered User
Hi, many thanks for the info. I figured there would be electronics in it.

As the MAF is rather expensive, is there anything else I can do to confirm it's faulty?

Since I posted this, I discovered the secondary air pump is also faulty and possibly the combi valve (according to my searches, gunk/water in the hoses indicates this) - could this be the cause of my bad cold starting?


Registered User
I mean it won't help, I'd fix that first then try the MAF after, but normally if you unplug it and it improves then its the MAF unfortunately. Try Autodoc, that's about the cheapest you'll get


Registered User
Hi Nate,
Many thanks for all your help. I looked at Autodoc, Bosch is £160. I'm in Ireland so would have tax on top of that, taking the cost to more than the car is worth (not that I'd mind that if it fixed it)!

I'll see if I can figure out the air pump first. Do you know if the combi valve for the air pump is the same thing as the EGR valve, as searching for combi valve brings up EGR. Also, where is the fuse/realy, it's not listed in the owners manual or in the fuse box itself.