How to read engine trouble codes ?

The first step to read the codes is setting the ECM in Diagnostic Test Mode II. Once the ECM is in Diagnostic Test Mode II, the "Service Engine Soon" warning light will start flashing. Count to flashes to determine the code. There are 10,000 different diagnoses your car can give, so putting your finger on the right one can be difficult. Figuring out how to fix the problem is another kettle of fish, but the first step is to know what your car is trying to tell you. The language it speaks is OBD, which stands for On Board Diagnostics.

What your mechanic probably won't tell you is that you really didn't need to shell out $100 just for them to hook up an OBD-II scanner to check on the service engine light. You can get that for free at most auto-parts stores. I've had this done at Napa and Advance Auto Parts. It costs nothing. The auto part stores carry these to cater to DIY'ers in hopes that they, in turn, buy the auto parts at their store to make the fix on their own. It takes them 1 minute to do this.

Step 1: Find Your Vehicle's Diagnostic Plug
The one in my car was a small blue plug that was bundled together with another factory plug beneath my glove box on the passenger's side of the car.

Step 2: Bridge the Wires
Get a paper clip or a piece of wire with the ends stripped off. Stick one end of the wire or paper clip in one of the holes in the plug and stick the other end in the other.

Step 3: Watch the Flashing Light and Decipher the Code
With the wire in place, put the key in the ignition and put the car into the "run" position. That's two clicks for Honda users.