http://www.mactools.com/entity/tabid...can-Tools.aspx

I have this MAC TOOLS ET50 OBDII scanner. A few months after getting this 1999 teh Service engine light came on. The code was for a minor vacuum leak. I thought maybe my daughter filled the car with gas while it was running.Also the defrost/heat select wasn't working so after digging I found the infamous Vacuum reservior hose off. I thought I had the problem solved. Well now she gets a Service engine light but the OBDII reader does not read any codes, NO CODES FOUND. I clear the codes only for it to come back with the same 'no code found' message.
Thoughts

 

Sorry for the slow response time. Forum problems at the beginning of the year meant a lot of new posts got missed. I do hope that you have cured your problem by now, if not, see below.

That scanner may not be able to access all of the systems that can trigger the SES light. On the 98+, there are a number of systems that communicate through a serial bus connection to the PCM and can trigger an SES light. Your scan tool does not look to be capable of serial bus communication (manufacturer specific).