Checking MAF wiring to ECM

[Heyobie]

I am having trouble with my MAF on my 2001 Beetle. I've tried 2 new MAF's and still getting CEL. I worked with a mechanic friend of mine who hooked up a $10,000 code reader and we watched the values that were being generated by the MAF. The codes were not happy with the Air Temperature sensor readings on the MAF. The reading was -41 degrees.

The guy printed out some documentation from his Mitchel software. Gave me a wiring schematic and instructions to test the MAF wiring to the ECM.

We felt that there was a wiring problem from the MAF. So I pulled the Large cable off of the ECM (left side) so that I could check the continuity of the wiring from the MAF connector to the ECM connector.

When I check for resistance the 4 wires of the MAF that go to the ECM, I get no reading. This means that all the wires are broken or I am doing something wrong. Obviously, it is the later.

The documentation that I have says to check the following.

MAF ECM Pin
1 - 40
2 - does not go to the ecm
3 - 12
4 - 11
5 - 13

My question is, 'Do I have the right ECM PIN numbers. For 11, 12 and 13, I am on the top row of the connector which starts with pin 6 (passenger side of car. I then am moving 5 pins toward the driver side for pin 11.

Also, can you tell which wire carries the MAF Air Temp?

Thanks,

Obie

[geniushanbiao]

I don't know the pin number on the ECM side. However I know that if you look at the connector it has 2 sides one is round and the other is square. If you start counting from the round side(not the square side), it's going to be 1,2,3,4,5. PIN1 is the air temp signal. PIN2 is the 12V power supply which doesn't go to ECM. PIN3 is Ground. PIN4 is 5V reference from ECM. PIN5 is MAF signal(air flow signal). Make sure you tested the 12V and 5V power supply and the ground wire before any work.

By the way, the 4 wires from MAF to ECM are: Blue/Green---Blue/Green, Brown/Blue---Brown/Blue, Violet/Red---Violet/Red, Blue---Blue. Make sure the wire color are correct when you check continuity.

[geniushanbiao]

Originally Posted by Heyobie

I worked with a mechanic friend of mine who hooked up a $10,000 code reader
Obie

And a good VAG-COM doesn't cost $10,000. You can buy the cable from ebay for like $10-20 and they usually come with a software. If you want a better one you can buy VCDS-Lite from Ross-tech for $99. So overall you can spend no more than $120 to get the proper VAG-COM and work out your vehicle with your own laptop.

Also I have to say, the code reader cost $10,000 doesn't mean it works good on your vehicle. VAGs are known to be prescriptive and ONLY VAG-COMs work the best on them. Once I had a code reader which can display and record real-time data but it always displays some weird data to me and made me confused. Later I got a VAG-COM cable and worked with VCDS-Lite then everything went well.

[Heyobie]

Genius,

Thanks for the help.

The P0102 I got from my ODB code reader was not even close to what my mechanic buddy got with his reader. So I need to get Vag-com just like everyone has been telling me since I got on this board.

Will the VDCS-lite help me resolve my problem? Is it just a code reader or will it show the values coming from the MAF?

The VAG-COM can not tell if there is a vacuum leak I assume.

Thanks for the pin numbers. Going to work on it again today.

Thanks

[Heyobie]

I ordered a VAG-COM connector today. So I should get a better read on the error codes.

Spent several hours on the 2001 Beetle.

Tested the 5 MAF wires with the car running.

Pin 1 - Air Temp Signal. Measured about 2.7V and a little more at 4000RPM. OK
Pin 2 - Measured about 13.5. Battery strength. OK
Pin 3 - Is a ground. I measured against Pin 2 and got the 13.5V. OK
Pin 4 - Was about 5V. OK
Pin 5 - Air Flow Signal. At idle, 1.45V and at 4000RPM 2.25. I think it is working fine

Measured the vacuum and it was a solid 23 at idle. No variation. So I conclude it is OK.

But I may have a problem with the fuel pressure. I connected a tee to the line going to the fuel rail. When I turned on the key, it only registered about 10 psi. I switched gauges to verify and it registered about 10 psi. When I started the car, it jumped up to the 40psi range. I could never duplicate the problem again. Maybe the first couple times with just the key on, the system couldn't handle all the air in the lines. I don't know

[geniushanbiao]

The VCDS-Lite is not a repair manual so it won't give you any instructions on how to solve the problem. However it gives you out the values the COMPUTER reads. For example the air flow in grams/second(g/s), the air temperature in C, etc. You can find the repair information on the website of Ross-tech.

Originally Posted by Heyobie

Genius,

Thanks for the help.

The P0102 I got from my ODB code reader was not even close to what my mechanic buddy got with his reader. So I need to get Vag-com just like everyone has been telling me since I got on this board.

Will the VDCS-lite help me resolve my problem? Is it just a code reader or will it show the values coming from the MAF?

The VAG-COM can not tell if there is a vacuum leak I assume.

Thanks for the pin numbers. Going to work on it again today.

Thanks

[geniushanbiao]

I don't think this is normal. The air flow at 4000rpm should be around 3V I think. But you can read the air flow data when you get the VAG-COM cable. The air flow at idle should be between 2.8-5.6g/s when hot. Let's say idle is 800rpm then at 4000rpm it should be 5 times which is 14-28g/s. This is the most accurate way.

The fuel pressure problem is normal. VW's fuel pumps are known weak and if you want to register pressure from 0(because you disconnected the fuel line), you have to cycle ignition for at least 3 times. Don't worry.

Originally Posted by Heyobie

I ordered a VAG-COM connector today. So I should get a better read on the error codes.

Spent several hours on the 2001 Beetle.

Tested the 5 MAF wires with the car running.

Pin 1 - Air Temp Signal. Measured about 2.7V and a little more at 4000RPM. OK
Pin 2 - Measured about 13.5. Battery strength. OK
Pin 3 - Is a ground. I measured against Pin 2 and got the 13.5V. OK
Pin 4 - Was about 5V. OK
Pin 5 - Air Flow Signal. At idle, 1.45V and at 4000RPM 2.25. I think it is working fine

Measured the vacuum and it was a solid 23 at idle. No variation. So I conclude it is OK.

But I may have a problem with the fuel pressure. I connected a tee to the line going to the fuel rail. When I turned on the key, it only registered about 10 psi. I switched gauges to verify and it registered about 10 psi. When I started the car, it jumped up to the 40psi range. I could never duplicate the problem again. Maybe the first couple times with just the key on, the system couldn't handle all the air in the lines. I don't know

[ronaldhead]

How do i check the wires to the maf?

[Heyobie]

Remove the plastic connector/band that holds the wires together at the back of the MAF. Start the car.

Put paperclips in the back of the wires you want to test so you could use a multi-meter. Check the voltage on lines 2 and 3. It should measure battery strength.

Then test Pins 1, 4 and 5 one at a time. They are the positive.

Pin 1 - Air Temp Signal. Measured about 2.7V and a little more at 4000RPM. OK
Pin 2 - Measured about 13.5. Battery strength. OK
Pin 3 - Is a ground. I measured against Pin 2 and got the 13.5V. OK
Pin 4 - Was about 5V. OK
Pin 5 - Air Flow Signal. At idle, 1.45V and at 4000RPM 2.25. I think it is working fine