Skip the auto shop - Our mechanics make house calls

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

asked by on

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.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!
  • Home
  • Questions
  • AC compressor drains the headlights and coolant indicator, check engine light is on

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: Sputtering issue with car

Code P0301 stands for cylinder #1 misfire. There are numerous potential causes for this code and your symptoms. If that is the only code stored, you'll want to focus on items specific to the #1 cylinder, such as the fuel...

Q: Compressor shaft seal leak

Hi and thanks for contacting YourMechanic. Put a manifold set (A/C gauge set) on the A/C ports and check the system when it is running on high A/C. Look to see what the pressures are on the high side and...

Q: High idling

This may be a sign of a failing idle air control valve. The idle air control valve is located on or near your intake manifold and monitors the air intake as it is mixed with fuel prior to being injected...

Related articles

P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...
P2428 OBD-II Trouble Code: Exhaust Gas Temperature Too High Bank 1
P2428 code definition A P2428 trouble code signifies that the PCM has detected a problem in the exhaust gas temperature sensor circuit in bank 1, which subsequently contains the number one...