For DIY, your basic tools should include a Helm manual, a MityVac, a DMM, & some jumper wires. You'll be crawling underneath, so you better have jackstands.

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Around here, the local AutoZoned or other parts stores will read the code for free, too. Get them to tell you the code number. Ours was mfg. specific, too, but he still saw the number, said it had something to do with a loose gas cap. I wrote down the number, & it WAS listed in the Helm manual.