Cruise Control Actuator Repair
04-18-2009, 10:05 PM
#1
Drifting
Thread Starter
Cruise Control Actuator Repair
I just repaired the Cruise Control Actuator on my 90’ S4. It had been non-operational for over a year, but just now did some troubleshooting and made a repair.
I’ve read that most failures are due to the cruise control amplifier, however mine was in the actuator. 88’ onward use this electrically assisted actuator; earlier cars have the vacuum assist actuator.
The trouble shooting was per the WSM procedure, Volume 1A, pages 27-22 through 27-24, is very quick and only requires disconnecting the amplifier plug and using a multi-meter on the plug pins.
Here’s the first page… Note the pin assignments.
Here’s the second page, note the measurements are clearly defined
My measurements:
Steps 1- 8, all satisfactory
Step 9 – measured 35 ohms, also sat.
Step 10 – measured 680 ohms, this is unsatisfactory, should be much lower resistance. If you look back at WSM page 7-21, you can see this measurement is between ‘engine plus’ and ‘engine minus’. This turns out to be the drive motor terminals. Glenn M reported similar measurement (1300 ohms) on his actuator in this post….
https://rennlist.com/forums/928-foru...-used-one.html
Steps 11 & 12 – measured 2.9K ohms, satisfactory.
You can also measure step 10’s reading at the actuator plug. Here’s the last page of the WSM, which shows the location of the actuator in the wheel well after removing the front wheel and wheel skin.
Differing from the WSM actuator removal method, I removed it from the bracket using a Craftsman Midget 10mm combination wrench. On my car, a standard 10mm combination was too thick to access the bolts against the car’s body.
Disassembling the actuator requires removing the lever arm (13mm wrench, counterhold with adjustable cresent wrench), 4 screws, after drilling off the head of one rivet. It’s best to center punch the rivet before drilling. Easy.
I also removed the motor cylinder which hold the top armature bearing and motor magnets. As you might expect the motor brushes and armature were in like new condition. You can’t remove the armature without removing the circuit board which is riveted to the housing.
Both the motor cover and the gear cover are o-ring sealed. These O-rings are reuseable.
Here’s a couple photos I grabbed from the 944 forum showing the guts of the actuator…. Same actuator part number as used on 944, 993, etc.
The problem with my actuator was a poor contact on the printed circuit board for the motor brush terminals (going to pins 1 and 7 in the photo). I could be wrong, but it looks to be a riveted contact, so not a cold solder joint. I applied new solder using a 40 watt soldering iron. I had to remove all three plastic gears from the housing to solder one of the motor terminals.
I’ve read that most failures are due to the cruise control amplifier, however mine was in the actuator. 88’ onward use this electrically assisted actuator; earlier cars have the vacuum assist actuator.
The trouble shooting was per the WSM procedure, Volume 1A, pages 27-22 through 27-24, is very quick and only requires disconnecting the amplifier plug and using a multi-meter on the plug pins.
Here’s the first page… Note the pin assignments.
Here’s the second page, note the measurements are clearly defined
My measurements:
Steps 1- 8, all satisfactory
Step 9 – measured 35 ohms, also sat.
Step 10 – measured 680 ohms, this is unsatisfactory, should be much lower resistance. If you look back at WSM page 7-21, you can see this measurement is between ‘engine plus’ and ‘engine minus’. This turns out to be the drive motor terminals. Glenn M reported similar measurement (1300 ohms) on his actuator in this post….
https://rennlist.com/forums/928-foru...-used-one.html
Steps 11 & 12 – measured 2.9K ohms, satisfactory.
You can also measure step 10’s reading at the actuator plug. Here’s the last page of the WSM, which shows the location of the actuator in the wheel well after removing the front wheel and wheel skin.
Differing from the WSM actuator removal method, I removed it from the bracket using a Craftsman Midget 10mm combination wrench. On my car, a standard 10mm combination was too thick to access the bolts against the car’s body.
Disassembling the actuator requires removing the lever arm (13mm wrench, counterhold with adjustable cresent wrench), 4 screws, after drilling off the head of one rivet. It’s best to center punch the rivet before drilling. Easy.
I also removed the motor cylinder which hold the top armature bearing and motor magnets. As you might expect the motor brushes and armature were in like new condition. You can’t remove the armature without removing the circuit board which is riveted to the housing.
Both the motor cover and the gear cover are o-ring sealed. These O-rings are reuseable.
Here’s a couple photos I grabbed from the 944 forum showing the guts of the actuator…. Same actuator part number as used on 944, 993, etc.
The problem with my actuator was a poor contact on the printed circuit board for the motor brush terminals (going to pins 1 and 7 in the photo). I could be wrong, but it looks to be a riveted contact, so not a cold solder joint. I applied new solder using a 40 watt soldering iron. I had to remove all three plastic gears from the housing to solder one of the motor terminals.
