Skip the auto shop - Our mechanics make house calls

Q: Disconnected 2ga wire from battery; rehooked, but warning light on

asked by on

After fixing the alternator, I was checking the voltage near the battery, from within the trunk. By accident, I unhooked a wire that goes from the battery to the distribution box. The car turned off. The wire that I had accidentally unhooked was a 2ga. I hooked it back in and the car started again. After that, there was an “engine malfunction reduced power” warning light on the dashboard. I disconnected the battery for 20 minutes, but the light is still staying on continually. What should I do to get the warning light to go off?

Hi, thanks for writing in about your 2006 BMW 740i. Disconnecting battery cables while the engine is running causes a voltage spike in the electrical system. Electronic control modules typically do not take this well! Sometimes this will damage some electronics, sometimes not. Sometimes the fix is reprogramming (reflashing) the engine control module. What you’ll need to do is have an experienced technician, such as one from YourMechanic, diagnose your BMW’s warning lights by using a compatible scan tool. Checking for fault codes will indicate what systems have been affected and provide a starting point for how it can be fixed.

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

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: Front brakes lock up is that the ABS module or the pump

The ABS system should of been put into bleed function when bleeding out the brake lines or you may not be able to get all the air out of the system. This is most likely the cause of the rear...

Q: Lighting bolt type light comes on when trying to start vehicle..but doesn't want to start...can't here the fuel pump kick in

A lighning bolt on the dash indicates that the electronic throttle control has an issue. It certainly can cause the vehicle to start and run rough or not at all, depending on the exact fault. You will need to scan...

Q: The interior lights and the head lights randomly flicker in Chevy Tracker

It could be the alternator. You can go and have any mechanic, anywhere take a look. Most guys do it free--they can check your batteries and alternator. It takes five minutes and they can tell you if the battery is...

Related articles

How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
P0052 OBD-II Trouble Code: HO2S Heater Control Circuit High (Bank 2 Sensor 1)
P0052 code definition HO2S Heater Control Circuit High (Bank 2 Sensor 1) What the...
What are the Car Pool Rules in Hawaii?
Hawaii is widely regarded as a land of vacation and relaxation, and as such, its scenic roads and routes are far better known than the state’s freeways. But, as with all...