Q: AC compressor drains the headlights and coolant indicator, check engine light is on

asked by on June 22, 2016

When I turn on my headlights I lose ground to the AC compressor. I also get a low coolant indicator and the drivers side headlight is dim and the passenger side headlight is a little brighter. The check engine light is on, too. When I run a ground wire from the front left battery to the AC compressor the compressor works and the headlights get brighter. After resetting the check engine light and turning the headlights off I don't get the check engine. The compressor works, too. So what should I do next?

You need to check the engine block grounds on the left and right side of the engine block. Follow the neg. cable down to the engine and make sure it is very tight. Another ground is on the radiator support for the body. After all the ground locations are checked and tightened and if the problem still happens, then the harness would need to be checked for a bad connection or splice. The most common cause is the battery cable being bad or the connections being loose. Have a mechanic diagnose the Check Engine Light codes to help pinpoint the problems that your car is experiencing.

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