poor man's fix for a bad cat

[carwilef7]

I kept getting a code 0702 (same as P0420) for a low right catalyst efficiency. This is probably a result of running with a weird fuel mix due to the previous owner's inattention to the bad MAF and a split TB boot, plus a bad coolant temp sensor that was causing a hot-start flooding condition (but the ECM never set a code for THAT).

 

Anyway, I ran the hell out of the truck with the O/D off so it would make the cat hot and burn off the accumulated goo,and it works for a few weeks, but I'm afraid it's no use. Keeps coming back. So I decided to bypass the CEL light.

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WARNING: If you live in an area that uses OBD II readiness or codes as part of your emissions/safety inspection, you will fail if you do this. My only goal was to not have to have the yellow light glaring in my eyes without spending $500 or more, and I don't have those hoops to jump through. Be sure to stay within your local regs, and no fault shall attach to me if you don't!

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I traced out the wire from the CEL/MIL light, and discovered that it runs off a 10 amp fuse along with a bunch of other things in the dash cluster. Apparently, the ECM, when it detects a code, closes a relay inside itself to ground the bulb circuit. It's on an orange wire going to the ECM near the center of the ECM plug. You will have to trace it out with your manual, or use a v/ohm meter to be sure.

 

I cut this wire when the CEL was on, so I could verify I had the right one, then spliced in a simple SPST switch and installed it in the plastic panel on the side of the console.

 

Now, I can drive around without the yellow glare, but I can easily turn the light on and read out the codes whenever I feel like it ( screw turn method - which I can explain if asked), and if anything goes catastrophically wrong I can reach it to turn it on to see if it's flashing, so I can pull over and shut the engine off quickly (hopefully in time to avoid major damage).