My 04 Quest has it's share of issues with shifting, but now I cannot get the my codes to erase. I have used a scan tool and they will not erase. It has been setting for about 3 months without a battery and when I put one in it the same lights were on as were on it 3 months ago. I have had the ECM checked and it was said to be fine. Any ideas? Thanks

Well, no battery connection will reset codes. Using a scan tool will reset codes. It sounds like you have codes as soon as you give power to the ECU (ECM, computer, etc.). You pull your codes without starting the Van right? You pull your codes after the reset and before starting your car right? It could be that the codes are for sensors that are completely disconnected and trigger the check engine light right away. What codes are you getting? Please post the numbers. Also, if you have a history of older numbers, please post those as well. Of course you want to keep the two lists separate. Historic codes and current/ present codes. Having a look at the particular codes will help confirm the above suspicion.

Thanks for the reply. Yeah I am actually getting all my dash lights coming on , ABS, Slip, TCS, and CEL plus a few others. They will not go away. But when I try to retrieve codes I get and error, like it cannot connect to retrieve them. I would suspect the ECM but like I said I sent it off to be tested and they said it was good. I know this year was known for the ECM water damage. I am stumped.

I have read that Faulty Speed Sensors can cause issues similar. What are your thoughts on that?

Well, I don't know about it all being related to the speed sensor, but that could cause a few issues with maybe TCS. We recently had a thread on here (earlier this year) where we talked someone out of buying an '04 Quest...
topic616259.html
In that thread, there was mention of corrosion on the ECU. Maybe that is related?

We do have the factory service manual (FSM). This link is to a page with links for each chapter. Starting with the FWD chapter, you'll find the Foreward and Table of Contents. The EC chapter will have most engine related electrical stuff you'd be looking for (CEL). The transmission chapter and brakes chapter may have things related to the other lights like SLIP, ABS and TCS.
http://www.nicoclub.com/FSM/Quest/2004_Quest/

Was having an issue reading codes as well, and I eventually developed the following process:
1. Connect the OBDII reader
2. Start the engine
3. Try to connect software (Scanmaster). There will be an error
4. Shut off the engine, turn ignition off and back on
5. Connect the software. This time w/o an error.