91-93 AFM testing pinouts

**ChazzyD** · #1 (**permalink**) 10-29-2009, 09:11 PM

Can anyone help with resistance values and pinouts to test the AFM, vane resistance and internal temp sensor pinouts? I have not been able to find that in the cardisc. The temp I'm pretty sure is the two outer pins and should abide by the usual Bosch AFM temp sensor charts I have seen in other publications. @ 68 degrees F, should be 2100-2900 Ohms rising with coldness and lower resistance with heat.
Charles

**Alfisto Steve** · #2 (**permalink**) 10-30-2009, 05:57 AM

S5 Air Flow Meter Test E Code 1221 page 617 wiring manual

Test Steps

E1 Meter Check

400 ohms pin 3 to 4
5 ohms pin 2 to 4
Manuall operate vane and check that resistance varies in a continious mode (without sudden variations).

Test I Code 1225 Engine Temp Sensor (ETS) failure in AFM page 622

Check resistance pin 4-5 according to temp chart [looks to be about same as for Coolant Temp Sensor readings]

Don't see a check using pin 1 is that an error in book maybe?

See wiring diagram page 597 for pins 1-5 inside AFM.

The 164S only has 4 pins whereas 164B/L AFM has 5.

**ChazzyD** · #3 (**permalink**) 10-30-2009, 12:55 PM

I'm getting 3360 ohms at the two outer pins (1 and 5) which would lead me to believe those are the proper pins to use for the temp sensor? Found those pages in the manual. They really don't spell things out as straight forward as I have read in manuals for other cars and may be in error as you say. Hmmmm.

**ChazzyD** · #4 (**permalink**) 10-30-2009, 01:07 PM

Has anyone adjusted the wipers in their meter so that the contacts run on fresh tracks? I'm thinking about doing this to mine. I think it may help my car run better. I had 4 slight hiccups on the drive to Atlanta and 1 on the way back on a long descent, throttle lifted. I'm thinking it is a symptom of worn AFM contacts, because it runs beautiful otherwise and can't find any other reason for the split second random dropouts.

OR, carbon tracks inside the IAC?
Charles

**Bremms** · #5 (**permalink**) 10-30-2009, 01:46 PM

I moved the wiper on my AFM and it does run better. Old Bosch AFM trick
so you dont have to get a new one... Some old BMW ones had a replaceable
potentiometer but no Alfa's do.

**ChazzyD** · #6 (**permalink**) 10-30-2009, 02:15 PM

YouTube - Rejuvenating a Bosch Motronic Air Flow Meter

**ChazzyD** · #7 (**permalink**) 10-30-2009, 04:08 PM

Pulled the thing to run some tests:
3 to 4 pin: 358 ohms should be 400
2 to 4: 132 should be 5 ????
4 to 5: 2383 temp sensor according to chart, that is good
2 to 3: vane test (move with finger slowly) shows that I have some dropout inconsistencies in a few places, SO maybe I've found my problem.
But, pulled the cover off and you can't move the wipers up or down on the AFM. It is fixed in position.

Do I have to oblong the pcb mounting holes and move that to get a fresh area for the wipers to run on?
Pin 1 is ground?
Charles

**Gubi** · #8 (**permalink**) 10-30-2009, 04:29 PM

Quote:

Originally Posted by ChazzyD

2 to 3: vane test (move with finger slowly) shows that I have some dropout inconsistencies in a few places, SO maybe I've found my problem.

**ChazzyD** · #9 (**permalink**) 10-30-2009, 04:47 PM

Unfortunately, he doesn't really show us what he is doing here with the test probes on the inside and the B/L AFM has 5 pins and not 4, so???? Where do we apply voltage in our case and where to get our readings on the inside? I cannot remove the plastic cover screws on this thing, because they are too tight to budge. They seem to be glued in, so no adjusting of the pcb.

Hitting a dead-end here.
Charles

**Bremms** · #10 (**permalink**) 10-30-2009, 07:58 PM

Cover is glued on, it should pry off. Screws in the back of the
AFM hold the door assy together

**ChazzyD** · #11 (**permalink**) 10-30-2009, 08:06 PM

I got the cover off, just not the rest of the plastic top that would have to be removed to adjust the printed circuit board to reposition it to run the wipers on virgin tracks. I suspect that pins 2 and 4 are supposed to be 100 ohms and not 5 ohms as the manual states. I have found on another thread that 100 is the correct number and upon re-reading mine I get 119 (seems to keep getting lower as the evening progresses

, weird). The other thread suggested 2 and 4 should be used to test the vane's varying resistance, the manuals instructions seems to mean that as well. Multiple pin combos along with moving the vane produces incremental resistance readings. Just wish the manual had spelled this out for us a little better and the 5 ohm on the 2 to 4 pin seems to be incorrect in the manual.
Charles

**Craig** · #12 (**permalink**) 10-31-2009, 01:52 PM

G'Day Guys,

Initial testing of AFM:

As Tom indicates 'resistance is futile' in respect of the airflow sensor.

Leave the afm in the car and roll back the cover on the connector this gives correct power supply and access to the wires.

Pin 1 (yellow black wire) CO pot output, With the ignition on and a voltmeter connected between pins 1 and 4, it should be roughly 2.5volts

Pin 2 (white black wire) airflow output. With the ignition on and a voltmeter connected between pins 2 and 4 set to the 20V scale, open and close the afm flap and observe the output voltage, it should change smoothly without jumping around. If it jumps around, the carbon track in the afm needs cleaning or the 'wiper' bent slightly so as to run on a new section of track.

Do not ever use CRC or RP7 or similar on the carbon track, you could destroy it. Use isopropyl alcohol for cleaning.

Pin 3 (Blue white wire) is the reference voltage from the ecu. around 5 volts

Pin 4 (green wire) is ground and all measurements should be with respect to ground.

Pin 5 (gray red wire) air temp output. With an ohmmeter connected between pins 2 and 5, the resistance should be as indicated in the chart in post 3 of this thread.

**Alfisto Steve** · #13 (**permalink**) 10-31-2009, 01:57 PM

Craig thanks for checking in with this info I was hoping you would. I added link to your post to my maintenance tips.

**ChazzyD** · #14 (**permalink**) 10-31-2009, 02:38 PM

Very nice Craig. I was about to just seal it back up and declare it "good." Now have some good info to go on. And there's the mysterious 5 as well. 5 volts at pin 3, ignition on. Thanks! I don't recall having an AFM thread with this detailed of info in it, so this is good to have as reference.
Charles

**ChazzyD** · #15 (**permalink**) 10-31-2009, 08:58 PM

Craig's info worked beautifully. Using his instructions, installed it in the car, ignition on. Pin 1 & 4 got 2.49 volts. Pin 2 & 4 got a smooth output of .252 volts up to a max of 4.78 volts and didn't see the wandering that I saw when I was measuring resistance. I did clean the carbon track with isopropyl alcohol since I had the cover off found that it did remove more dirt than I expected to see. I did not see any worn spots that looked worn completely through and it actually looked much more healthy after the cleaning. Pin 3 & 4 gave me 4.99 volts. Pin 2 & 5 gave me 2380 ohms @ probably around 70* F in the garage. So all is well with it. Thanks again Craig! It's sealed back up and now I'm ready to move on to the timing belt replacement. (that time again already

)
Charles