1st Issue

 

I was wondering if someone could point me in the right direction here.

 

I had a 17837 code which is Circuit for Brake Vacuum Pump: Open Circuit

 

Manage to find the hidden unlisted and not very well documented fuse on the just above the accelerator pedal once I'd removed the plastic cowling above the pedals. Replaced and Voila the fault cleared, however I did an output test and when it gets to the brake booster control module (J542) there is silence, nothing functions.

 

http://www.volkspage.net/technik/ssp/ssp/SSP_257.pdf Upon reading this, it appears that the Brake Vacuum Pump is this (j542 module) which is integrated into the Secondary Air Injection pump. My question is am I correct in assuming this? 

 

I appears that the pump is seized, it doesn't make a noise, I've checked the fusible link for the secondary air injection (SAI) Pump as it appears intact, again when I run an output test in Vagcom, silence.

 

2nd Issue 

 

Also had the 17704 "Error in Mapped Cooling System" fault in Vag-Com, so I replaced Thermostat and OEM New Style Temperature Sender. The engine seems to dip around 75c and take forever to warm up, if it's left idling it will stay at 90c all day longer. It had better behaviour before the change but wouldn't sit at 90c all the time.

 

Can anyone tell me the nature of the 1.8T 20V and where it should sit. Faulty Thermostat, it replaced an 87c open with an 87c and my MPG has fallen slightly. 2-3 MPG, advise.

 

 

 

 

 

 

 

#1 - Do you have a heavy brake pedal? If not then I'm pretty sure the brake servo vacuum supply is working normally.

 

The "secondary vacuum pump" is an emissions control measure, and nothing to do with the brakes.