HVAC Blower Motor not working on any setting

[Joneser2002TT]

2002 Audi TT Quattro 225 manual 55k miles like new, car is garaged. HVAC Blower motor not working on any setting. It stopped working, then I removed motor and checked with 12V (battery direct) and motor works, reassembled under dash, and it worked for a few minutes. Then quit again. Fan speed display shows high, but then bars drop down, and cycle repeats. I can hear noises like attempts are being made to open flaps (?) under dash. Pulled motor and it ran fine on batery 12V. Checked ground with test light directly on battery and ground is fine. Checked motor continuity while slowly turning manually and no breaks. Removed battery and replaced connectors at the ground terminal under the battery after finding some very minor green corrosion between connectors and wire. Replaced resister (new). Swapped out HVAC controller with used (ebay), motor and display behaves the same. Checked voltage going to motor and it is only receiving 2.5 - 3V no matter what the speed setting. Removed the entire lower dash and center stack to inspect harness. Found one tiny mouse poop, but no evidence of chewed harness that I can see. Maybe dead mouse is blocking the operation of the flapper doors inside the HVAC port? I'll try to find using a camera probe. Edit: removed center console (between seats) and found more evidence of mouse infestation: chewed insulation piles, bits of corn chewed up, and pee stains. No chewed harness evidence. Connectors all looked clean. Will pull up the wire harness diagram next to trace circuit.

Here are the codes:

Monday,06,April,2026,14:15:50:25529
VCDS -- Windows Based VAG/VAS Emulator Running on Windows 10 x64
VCDS Version: 26.3.0.0 (x64)  HEX-V2 CB: 0.4701.5
Data version: 20260320 DS375.1
www.Ross-Tech.com

Dealer/Shop Name: Jeff K Jones

Chassis Type: 8N - Audi TT (1999 > 2007)
Scan: 01 02 03 08 15 17 22 35 37 45 55 56 76 77
 
-------------------------------------------------------------------------------
Address 01: Engine        Labels: 06A-906-032-AMU.lbl
   Part No: 8N0 906 018 AN
   Component: 1.8L R4/5VT     G   0004
   Coding: 06710
   Shop #: WSC 01236
   VCID: 7DA021D804E75572A45-5160
   TRUWT28N721023906     AUZ5Z0B1156014

6 Faults Found:
16795 - Secondary Air Injection System
            P0411 - 35-10 - Incorrect Flow Detected - Intermittent
17978 - Engine Start Blocked by Immobilizer
            P1570 - 35-10 -  - Intermittent
17544 - Fuel Trim: Bank 1 (Add)
            P1136 - 35-10 - System too Lean - Intermittent
18010 - Power Supply Terminal 30
            P1602 - 35-10 - Voltage too Low - Intermittent
17069 - ECM Power Relay Control Circuit
            P0685 - 35-10 - Open Circuit - Intermittent
18058 - Powertrain Data Bus
            P1650 - 35-00 - Missing Message from Instrument Cluster
Readiness: 0000 0000

-------------------------------------------------------------------------------
Address 03: ABS Brakes        Labels: 8N0-907-379-MK60-A.lbl
   Part No: 8N0 907 379 H
   Component: ESP ALLRAD MK60     0101
   Coding: 0022544
   Shop #: WSC 01236 785 00200
   VCID: 41D89D283D9FF19280D-5160

3 Faults Found:
00810 - Sensor 1/2 for Brake Pressure
            008 - Implausible Signal - Intermittent
00813 - Sensor 2 for Brake Pressure (G214)
            008 - Implausible Signal - Intermittent
00493 - ESP-Sensor Unit (G419)
            014 - Defective

-------------------------------------------------------------------------------
Address 08: Auto HVAC        Labels: 8N0-820-043.lbl
   Part No: 8N0 820 043 A
   Component: TT-KLIMAVOLLAUTOMAT D03
   Coding: 00140
   Shop #: WSC 01236
   VCID: 280E208CBBE520DAA73-258E

3 Faults Found:
00600 - Potentiometer On Positioning Motor for Temperature Flap (G92)
            30-10 - Open or Short to Plus - Intermittent
01273 - Fresh Air Blower (V2)
            17-10 - Control Difference - Intermittent
01582 - Signal for Coolant Temperature
            30-00 - Open or Short to Plus

-------------------------------------------------------------------------------
Address 15: Airbags        Labels: 8N0-959-655.lbl
   Part No: 8N0 959 655 A
   Component: Airbag Front+Seite 5000
   Coding: 01103
   Shop #: WSC 01236
   VCID: 3E22E6D449618E6AFDF-5156

10 Faults Found:
65535 - Internal Control Module Memory Error
            00-10 - - - Intermittent
65535 - Internal Control Module Memory Error
            00-10 - - - Intermittent
65535 - Internal Control Module Memory Error
            00-10 - - - Intermittent
65535 - Internal Control Module Memory Error
            00-10 - - - Intermittent
65535 - Internal Control Module Memory Error
            00-10 - - - Intermittent
65535 - Internal Control Module Memory Error
            00-10 - - - Intermittent
65535 - Internal Control Module Memory Error
            00-10 - - - Intermittent
65535 - Internal Control Module Memory Error
            00-10 - - - Intermittent
65535 - Internal Control Module Memory Error
            00-10 - - - Intermittent
65535 - Internal Control Module Memory Error
            00-10 - - - Intermittent

-------------------------------------------------------------------------------
Address 22: AWD        Labels: 02D-900-554.lbl
   Part No: 02D 900 554 C
   Component: HALDEX LSC  ECC     0010
   VCID: 201E38ACD3D5D89AEF3-4B1E

No fault code found.

-------------------------------------------------------------------------------
Address 35: Centr. Locks        Labels:. 8Nx-962-267.clb
   Part No: 8N8 962 267 A
   Component: Central Lock/Alarm  D06
   Coding: 15976
   Shop #: WSC 09480
   VCID: 3FDC9BD04E6B8762F69-4F30

1 Fault Found:
01370 - Alarm triggered by Interior Monitoring
            35-00 - -

-------------------------------------------------------------------------------
Address 37: Navigation        Labels: 4B0-919-887-BNS4.lbl
   Part No: 4B0 919 887 E
   Component: BNS 4.2 H05    BNO 0007
   VCID: 3530F9F87C574D322C5-4B02

No fault code found.

-------------------------------------------------------------------------------
Address 45: Inter. Monitor        Labels: 8E0-951-177.lbl
   Part No: 8N8 951 177 A
   Component: Innenraumueberw.    D09
   Coding: 00001
   Shop #: WSC 00000
   VCID: 3D20E1D844679572E45-5176

1 Fault Found:
01463 - Alarm triggered by Sensor for anti-theft alarm System
            35-00 - -

-------------------------------------------------------------------------------
Address 55: Headlight Range        Labels: 4B0-907-357-AUT.lbl
   Part No: 4B0 907 357
   Component: LEUCHTWEITEREGLER  D004
   Coding: 00010
   Shop #: WSC 01236
   VCID: 659069B88C77FDB25C5-51FA

No fault code found.

End----------(Elapsed Time: 02:41, VBatt start/end: 12.1V/12.1V)-----------
------------------------------24 Faults Found------------------------------

Thank you all for your assistance,

Jeff Jones
Evergreen, Colorado

 

[Jef]

Checked voltage going to motor and it is only receiving 2.5 - 3V no matter what the speed setting.

What side of the blower motor (V2) are you getting 3V?

• /1 is a black/blue wire that comes off fuse S255 (25A).
• /2 is a brown/red that is a controlled ground via the Fresh air blower control unit (J126).

Since the blower motor seems to be OK when hotwired, and the HVAC control head being swapped didn't change anything, then I would double check wiring harness and that J126.

 

[Ziddywerks]

Bad resistor pack most likely cause if you ask me or blower motor itself. if blower motor works at full speed in the vehicle then its garanteed that the resistor pack is no good. Source of resistor pack?

 

[Dr Sheldon]

I have just looked at the wiring diagram for this - Blower Control via Switch and Resistor Pack.

It is very Straight forward !

 

[Dr Sheldon]

ws = white
sw = black
ro = red
br = brown
gn = green
bl = blue
gr = grey
li = purple
ge = yellow
or = orange
rs = pink

Fresh air blower
E9 - Fresh air blower switch
E159 - Fresh air/air recirculating flap switch
N23 - Fresh air blower series resistor
N24 - Fresh air blower with overheating fuse series resistor
T4c - 4-pin connector, behind console
V2 - Fresh air blower
V154 - Fresh/recirculating air flap control motor
44 - Earth point, lower part of left A pillar
162 - Earth connection, in blower motor wiring harness
B135 - Connection (15a), in interior wiring harness
L66 - Connection, in heater blower wiring harness

 

[Joneser2002TT]

Thank you Dr Sheldon! Let the troubleshooting begin! BTW I have been to your town Windsor back in 1995. Toured the Castle. Love the UK.

 

[Joneser2002TT]

ws = white
sw = black
ro = red
br = brown
gn = green
bl = blue
gr = grey
li = purple
ge = yellow
or = orange
rs = pink

Fresh air blower
E9 - Fresh air blower switch
E159 - Fresh air/air recirculating flap switch
N23 - Fresh air blower series resistor
N24 - Fresh air blower with overheating fuse series resistor
T4c - 4-pin connector, behind console
V2 - Fresh air blower
V154 - Fresh/recirculating air flap control motor
44 - Earth point, lower part of left A pillar
162 - Earth connection, in blower motor wiring harness
B135 - Connection (15a), in interior wiring harness
L66 - Connection, in heater blower wiring harness

Dr Sheldon, is the above diagram for a 2002 TT 225 1.8 Quattro, Mk1 (8N)? I ask because the colors are not matching up. The two wires that go to my blower motor are Brown/Red (-) and Blue/Black (+). Your diagram shows Brown (-) and Yellow (+). When I turn on the blower motor I get 1.6V across them no matter what speed the controller is set to. Minor good news, the flapper doors all operate for (1) fresh air/recirc/defrost, (2) A/C and (3) heater as called for by the controller.

Jeff

 

[Joneser2002TT]

Bad resistor pack most likely cause if you ask me or blower motor itself. if blower motor works at full speed in the vehicle then its garanteed that the resistor pack is no good. Source of resistor pack?

Ziddywerks: I can't remember where I got the Resistor, but it was from an online source (new). The part marking is ITR-Leistungsmodul. The blower motor doesn't work on any speed setting. There are three wires going to the resistor: Brown (-), Brown/Red (.9V), Green/Black (9.6V). Those voltages are measured to the brown wire which I assume is ground, and do not change with fan speeds called for by the controller.

 

[Joneser2002TT]

What side of the blower motor (V2) are you getting 3V?

• /1 is a black/blue wire that comes off fuse S255 (25A).
• /2 is a brown/red that is a controlled ground via the Fresh air blower control unit (J126).

Since the blower motor seems to be OK when hotwired, and the HVAC control head being swapped didn't change anything, then I would double check wiring harness and that J126.

When I measure across the two wires that connect to the blower motor I get 1.6V now, independent of fan speed called for by the controller. Blue/Black (+) and Brown/Red (-). Minor good news is that all three flapper motors are working well: (1) fresh air/recirc/defrost, (2) A/C and (3) heater when called for by the controller. No dead mouse blocking the flaps.

 

[Dr Sheldon]

Dr Sheldon, is the above diagram for a 2002 TT 225 1.8 Quattro, Mk1 (8N)?

It should be however I guessed at some of it because I do not see Engine Code nor Vin in your thread !!

Add to that I am in the Uk and maybe I do not see the NAR models (are they different) ?

 

[MVB_]

Seem like you are describing this WD

 

[Joneser2002TT]

It should be however I guessed at some of it because I do not see Engine Code nor Vin in your thread !!

Add to that I am in the Uk and maybe I do not see the NAR models (are they different) ?

Here's what I posted in the first thread from the engine module:
Address 01: Engine
Labels: 06A-906-032-AMU.lbl<br>
Part No: 8N0 906 018 AN<br>
Component: 1.8L R4/5VT G 0004<br>
Coding: 06710<br> Shop #: WSC 01236<br>
VCID: 7DA021D804E75572A45-5160<br> TRUWT28N721023906 AUZ5Z0B1156014

I guess maybe the UK models are different...although that seems weird.

 

[Joneser2002TT]

Seem like you are describing this WD

View attachment 5256

Yes! Thank you MVB

 

[Dr Sheldon]

Yes! Thank you MVB

Then this makes a complete nonsense of your text

Replaced resister (new)

There is no Resistor pack N24 in that Set Up. The part you replaced ???

Rather it has J126 which is a PWM module controlling the Blower Fan Speed on the negative side !



I did initially wonder about the "Resistor" when I saw this

Component: TT-KLIMAVOLLAUTOMAT D03

Which translates to = CLIMATE AUTOMATIC

 

[Joneser2002TT]

Then this makes a complete nonsense of your text


There is no Resistor pack N24 in that Set Up. The part you replaced ???

Rather it has J126 which is a PWM module controlling the Blower Fan Speed on the negative side !



I did initially wonder about the "Resistor" when I saw this

Which translates to = CLIMATE AUTOMATIC

I replaced this electronic component with a heat sink on it. It is identified on a wiring diagram I have as the Fresh Air Blower Control Module - not a "resister" as it is refered to many times elsewhere on the internet.

 

[Dr Sheldon]

as it is refered to many times elsewhere on the internet.

Bollox to the Internet !!

You Wrote !!

Replaced resister (new)

You said you replaced the "RESISTOR" Wasted Time and threw me off track !!

Don't backtrack now !!

 

[Joneser2002TT]

Bollox to the Internet !!

You Wrote !!


You said you replaced the "RESISTOR" Wasted Time and threw me off track !!

Don't backtrack now !!

So after doing some reading, it actually is a resistor. That's why it has a huge heat sink behind it. Audi (and many other car manufacturers) chose to control the fan speed automatically, using a resistor in the ground path to alter potential, instead of varying the voltage directly using a Pulse Width Modulator (PWM). Now I need to figure out how to check my resistor (fresh air blower control module) to find out if it is good.

 

[Joneser2002TT]

What side of the blower motor (V2) are you getting 3V?

• /1 is a black/blue wire that comes off fuse S255 (25A).
• /2 is a brown/red that is a controlled ground via the Fresh air blower control unit (J126).

Since the blower motor seems to be OK when hotwired, and the HVAC control head being swapped didn't change anything, then I would double check wiring harness and that J126.

Jef, I did some reading and looking at the 8N wiring diagram (from Mitchell Repair Information Company), and see that this circuit to control blower fan speed uses a constant 12V on the black/blue (+) side, and varies the resistance to ground (-) using the resistor (called "fresh air blower control module" BCM) with a large heat sink (photo below). So I verified that the 12V is getting to the motor on the black/blue wire (voltmeter, key on), so the fuse and relay are working properly. Now to check the harness. The BCM has three wires: brown lead #3 (ground) verified connector to chassis ground (.5 Ohms); brown/red, lead #2 verified continuity with blower motor connector (.5 Ohms) and A/C Control Head (ACCH) (C11) connector (.5 Ohms); green/black lead # 1 verified continuity to ACCH C16 connector (.5 Ohms). (Note: my cheap volt meter instrument shows .5 Ohms when I touch the leads directly together, so I am counting that as "good" continuity.) So to my mind, the harness is good from the motor through the BCM to the ACCH. Next I'll check the BCM using resistence across the three leads. Need to find what the values should be. There are no signs of heat-related wear, either discoloration or melting around the leads or the heat sink.

Jeff

 

[Joneser2002TT]

Jef, I did some reading and looking at the 8N wiring diagram (from Mitchell Repair Information Company), and see that this circuit to control blower fan speed uses a constant 12V on the black/blue (+) side, and varies the resistance to ground (-) using the resistor (called "fresh air blower control module" BCM) with a large heat sink (photo below). So I verified that the 12V is getting to the motor on the black/blue wire (voltmeter, key on), so the fuse and relay are working properly. Now to check the harness. The BCM has three wires: brown lead #3 (ground) verified connector to chassis ground (.5 Ohms); brown/red, lead #2 verified continuity with blower motor connector (.5 Ohms) and A/C Control Head (ACCH) (C11) connector (.5 Ohms); green/black lead # 1 verified continuity to ACCH C16 connector (.5 Ohms). (Note: my cheap volt meter instrument shows .5 Ohms when I touch the leads directly together, so I am counting that as "good" continuity.) So to my mind, the harness is good from the motor through the BCM to the ACCH. Next I'll check the BCM using resistence across the three leads. Need to find what the values should be. There are no signs of heat-related wear, either discoloration or melting around the leads or the heat sink.

Jeff

So clearly there is a signal coming from the green/black wire from the ACCH that varies the continuity between the brown ground wire (chassis) and the brown/red wire that goes to the blower motor. Right now, the measured resistance between the two brown wires is OL. I turned up the fan speed to high on the ACCH, and measured the voltage coming out of the green/black pin C16 and got 9.6V. I clearly need a bench test station where I can input voltages and measure components. I ordered a variable DC power supply, will get here Thursday.

 

[MVB_]

So you swapped a used E87 and you still did not have high blower speed?