check engine light not throwing any codes

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I have a 2005 chevy tahoe 5.3 ltre vortec engine. about a month and a half ago my wife was driving it and some jack hole parked in front of my house hit her as she was pulling into my driveway. my problem is that ever since the accident the check engine light comes on and goes off periodically. it initially comes on when i step on the gas. but it's not throwing any codes, i plug my OBD2 reader into the truck, nothing. my owners manual says could be a vacuum leak.i've seearched the engine compartment top to bottom and have only found two lines, tested them with a bottle of brake clean, no leaks. any suggestions?

[txab]

Could be ABS and your code reader may not read ABS codes