Central flap motor - No reaction to activation, signal unclear: Diagnosis/troubleshooting

DIAGNOSIS/TROUBLESHOOTING (FAULT CODE 27, AS OF MY 2002)

Work instruction			Display OK	If not OK
1	Read out air-conditioning system fault memory		Only fault code 27 entered Step 2 Fault code 27 and 26/28/29 entered Step 8 Fault code 27 and 25 entered See 'SUPPLY VOLTAGE SENSORS (5 V) - TOO HIGH/TOO LOW/SHORT CIRCUIT TO B+/GROUND SHORT ' Fault code 27 and 26/28/29 and 21/22/23 entered Step 10
2	Visual inspection	Ignition off Remove connector from servo motor for temperature mixing valve Check connector for contact and corrosion Check flap for stiffness	Connector OK Step 3	Clean connector or plug in correctly or repair flap -> End
3	Check 5 V - supply line to central flap servo motor	Ignition on Measure voltage at connector of the central flap between pin 1 and ground Measure voltage between pins 1 and 3 on central flap connector	Approx. 5 V Step 4	Step 7
4	Check signal lead and servo motor lines for short circuit to B+	Ignition off Remove connector B from the air-conditioning system regulator Remove connector D from the air-conditioning system regulator Ignition on Measure voltage between pin 14 and ground on connector B Measure voltage between pin 12 and ground on connector D Measure voltage between pin 4 and ground on connector D	< 0.3V Step 5	Repair wiring harness -> End
5	Check signal lead and servo motor lines for short circuit to ground	Ignition off Measure resistance between pin 14 and ground on connector B Measure resistance between pin 12 and ground on connector D Measure resistance between pin 4 and ground on connector D	Step 6	Repair wiring harness -> End
6	Check signal line and servo motor line for interruption	Ignition off Measure resistance between connector B on the air-conditioning system regulator pin 14 and connector on central flap pin 2 Measure resistance between connector D on the air-conditioning system regulator pin 12 and connector on central flap pin 6 Measure resistance between connector D on the air-conditioning system regulator pin 4 and connector on central flap pin 4	< 5 Step 11	Repair wiring harness -> End
7	Check 5 V supply line for short circuit to B+	Ignition off Remove connector B from the air-conditioning system regulator Ignition on Measure voltage between pin 20 and ground on connector B	< 0.3V Step 8	Repair wiring harness -> End
8	Check 5 V supply line for short circuit to ground	Ignition off Measure resistance between pin 20 and ground on connector B	Step 9	Repair wiring harness -> End
9	Check 5 V supply lead for open circuit	Ignition off Measure resistance between connector B on the air-conditioning system regulator pin 20 and connector on central flap pin 1	< 5 Step 10	Repair wiring harness -> End
10	Check ground line for open circuit	Ignition off Measure resistance between connector B on the air-conditioning system regulator pin 9 and connector on central flap pin 3	< 5 Step 12	Repair wiring harness -> End
11	Servo motor for central flap		-> End
12	Replace air-conditioning system regulator		-> End