Potential Causes: 

  • Refrigerant ————————————————-eliminated by pressure check of gases by Bill
  • Fuse
  • Battery Auxiliary Fuse Box
  • A/C Compressor ——————————————eliminated by checking continuity of clutch coil
  • A/C Pressure Sensor F129
  • A/C Switch, Ambient Temperature Switch F38
  • Fan Control Module J293 and its Wiring
  • Lost Throttle Basic Settings —————————- eliminated by running engine at rpm >2500

VW Golf Mk4 FCM Fan Control Module  


  •  VW Golf Mk4 FCM == Fan Control Module  P/N == 1J0919506K
  • AC Pressure Switch – Audi TT VW Jetta Golf MK4 Beetle A/C Sensor – 1J0 959 126


My Debug CheckList

  1. Pressure check shows adequate refrigerant
  2. Disconnected A/C clutch connector – measured about 4 ohms with a multimeter.  Appears good. See video link #1
  3. Note: Pin T14/3 will be grounded by the ECM if the throttle basic settings are lost. Raising the engine rpm over 2,500 will cause the ECM to allow A/C operation if this is the case. If a ground condition exists on pin 3, perform a throttle basic setting procedure and recheck for correct voltage.  — I test drove the car in 2nd gear to force the rpm >2500.  This did not appear to turn the clutch on. See research link #1

Research Links

  1. Tech Tip: Volkswagen Has No Power to the A/C Compressor Clutch  – The A/C clutch connector is depicted in the early part of this video – See debug checklist point #1


Videos Links

  1. YouTube: MK4 JETTA A/C clutch repair
  2. YouTube: VW A1 A2, A3, A4: Radiator fan(s) quick check  – Starts with the battery fuse plate and works through the radiator fan connectors.  A1,A2,A3,A4 refer to the Audi platform which is used company wide as the basis for all their cars.
  3. YouTube: 2005 Volkswagen Passat 1.8T- A/C Blows Warm
  4. YouTube: Changing a fan control module for Mk4 VW – removes the battery tray to get at the FCM
  5. YouTube: VW/Audi Fan Relay Cooling Fan Control Unit Module Relay – Shows the connectors up close and how to unplug them.  Commented in the video how these FCM units are a weak link in the design



VW Mk4 Fuse Panel

Fuse Locations and Functions 
1. Washer nozzle heaters, glove compartment light (10A). 
2. Turn signal lights (10A). 
3. Fog light relay, instrument panel light dimmer switch (5A). 
4. License plate light (5A). 
5. Comfort system, cruise control, A/C, steering wheel module (7.5A).   
6. Central locking system (5A). 
7. Back-up lights, speedometer vehicle speed sensor (VSS) (10A). 
8. Open 
9. Anti-lock brake system (ABS) (5A). 
10. Engine control module (ECM): gasoline engine (10A) 
11. Instrument cluster, shift lock solenoid (5A). 
12. Data Link Connector (DLC) power supply (7.5A). 
13. Brake tail lights (10A). 
14. Interior lights, central locking system (10A). 
15. Instrument cluster, transmission control module (TCM) (5A). 
16. A/C clutch, after-run coolant pump (10A).                                         
17. Open. 
18. Headlight high beam, right (10A). 
19. Headlight high beam, left (10A). 
20. Headlight low beam, right (15A). 
21. Headlight low beam, left (15A). 
22. Parking lights right, side marker right (5A). 
23. Parking lights left, side marker left (5A). 
24. Windshield washer pump, windshield wiper motor (20A). 
25. Fresh air blower, A/C (25A). 
26. Rear window defogger (25A). 
27. Motor for rear windshield wiper (15A). (if equipped) 
28. Fuel pump (FP) (15A). 
29. Engine control module (ECM) gasoline engine (15A) 
30. Power sunroof control module (20A). 
31. Transmission control module (TCM) (20A). 
32. Injectors: gasoline engine (10A) 
33. Headlight washer system (20A). 
34. Engine control elements (10A). 
35. 12 V power outlet (in luggage compartment) (30A). 
36. Fog lights (15A). (if equipped) 
37. Terminal (86S) on radio, Instrument cluster (10A). 
38. Central locking system (w/ power windows), Trunk light, fuel door, Trunk lid (15A). 
39. Emergency flashers (15A). 
40. Dual tone horn (20A). 
41. Cigarette lighter (15A). 
42. Radio (25A). 
43. Engine control elements (10A). 
44. Heated seats (15A). (if equipped) 


Auxiliary Issues

Error codes 16684 and 16685:  Missing on cylinder 1

16685: Cylinder 1 Misfire Detected
Possible Causes

* Ignition system
* Fuel injectors
* Fuel pressure
* Running out of fuel
* EVAP canister purge valve
* Evaporative emission system
* Low compression
* Base engine problems
* Controle Module damaged 

Special Notes: This feature search for engine misfire in a specific cylinder. Most of the time the cause for a misfire is a lack of combustion in a cylinder due to absence of spark, poor fuel metering, or poor compression.

16684: Random/Multiple Cylinder Misfire Detected

Possible Causes

* Air Intake System leaking
* Fuel Supply faulty
* Injector(s) faulty
* Ignition Cable(s) and/or Spark Plug(s) faulty
* Ignition Coil(s) faulty
* Exhaust Gas Recirculation (EGR) Valve (N18) stuck/open
* Camshaft Position Sensor (G40) faulty 

Possible Solutions

* Check Misfire Recognition
* Check Air Intake System
* Check Fuel Supply
* Check Injector(s) and Injector Sealing
* Check Ignition Cable(s) and Spark Plug(s)
* Check Ignition Coil(s)
* Check Exhaust Gas Recirculation (EGR) Valve (N18)
* Check Camshaft Position Sensor (G40) 


  • Spark plugs had a lot of wear.  I suspect they had never been changed on this car as of 92kmiles.  Replacement resulted in the misfire codes not returning.  See photo below.

eroded spark plugs


Junk Yard Shopping List

  • Ignition coil
  • FCM – fan control module
  • AC refrigerant pressure sensor











Categories: Cars

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