2004 S-600
 

Typical start up. ....Engine starts and runs very smothe. It may run smothe all day, no problems. Then at times it will go in half power mode. I will shut it off then start it again and it will run smothe. I never know when this will happen. Where do I start, what do I check out first. ... ECU ??? ...

CEL came on in idle mode?

coil packs or voltage transformer on top of the engine

You can rent them at v12icpack.com to narrow down what is at fault . Start with the transformer first

First step is get a cheap OBD2 diagnostic code reader to download the fault codes. Every MB owner should have one.

Do you know what I mean by that?

Nick

I had the same problem on my 02. For me it was the voltage transformer.

If you want, contact Clark Rupp over at v12icpack.com He let's you 'rent' the voltage transformer.

My 03 S600 did the same. Put Right coil pack, had the transformer check, it was a bad ECU by the time I was done. Cars been perfect for over a year now.

You're not at this stage yet, but if it is the ECU, we can repair it for you for a lot cheaper than what your dealer will charge you. Click here if and when you need us.

your charge to repair is over $150 more than m and b charges to repair a ecu

Excellent point, over the years we have helped 70,000 people get their rides back on the road. Nothing against M & B, mainly because we're unsure of who you are talking about, it's our reviews that set us apart from our competitors. It all comes down to service, and the name backing the guarantee.

How can you tell if ECU good or bad? Is it a test with STAR system?

My 03 started to create over problems on top of misfiring, with and without codes.