BACKYARD MECHANIC: Bad ground connection can trigger wipers

Hey there, time traveller!
This article was published 27/04/2012 (4942 days ago), so information in it may no longer be current.

QUESTION: I have a 2011 Dodge Journey and have an unusual problem. I have been putting an aftermarket audio system into the vehicle and removed the seats and carpet to run wiring. The problem is with the windshield wipers. Even though the key isn’t on, the wipers will run in low speed and can’t be turned off. I unplugged the wiper motor to stop them but as soon as I plug it back in they start operating again. It doesn’t matter whether the key is on or off. Can you tell me how to get them operating normally again?

ANSWER: Would you believe the system is operating normally? Actually, this is a problem with grounding systems and what technicians commonly call backfeeds. When you disconnected electrical connections to remove seats, console, etc. you interrupted the ground connection for several modules and computers in the vehicle. This could include air bag modules, seat heaters, power seats, seat position sensors, audio controls and so on. To determine exactly what has no ground would involve looking at wiring diagrams and each electrical connector that you opened.

When a device has no ground but still has power from a source, the electricity in the device will try to find a ground in the easiest path possible. The ground could come from a common connection to another device, such as the wiper circuit. The current would flow backwards through the common connection into the wiper control module and then ground through the wiper ground. Sometimes this causes other devices to operate, such at turning on the wipers in your Journey.

Fortunately the repair is relatively easy. Reconnect all the disconnected modules and the wipers will work as they should. I have seen this happen on other Journey vehicles and on a Ram pickup as well, so you are not the first to experience this.

Another example I ran across was when I disconnected a ground connection under the rear seat of a newer Cadillac STS. Even though the keys were not in the vehicle, the radio started to play and the headlights came on. Sometimes the world of automotive electronics seems very complicated, but it is often something as simple as finding the bad ground connection.

QUESTION: My son has an older 2002 Saturn sedan and the car is making loud noises and leaking. The car has a four-cylinder engine and manual transmission. The engine runs fine but when we try to drive, it makes crunching sounds and doesn’t want to go. There is some oil on the ground beneath the centre of the engine compartment but I can’t see where it is coming from. Do you have any idea what may be wrong? We would like to get the car going again but don’t have a lot of money for repairs.

ANSWER: Your Saturn doesn’t sound healthy. Since the engine still runs fine, I would suspect the transmission is at fault. If there wasn’t oil leaking, I would suggest looking at the shift cable attachments on top of the transmission first, but since you do have oil leaking, I would now try to see where it is coming from.

I suspect the oil leak is from a hole in the transmission case. I have seen this happen several times, and not only on Saturn cars! Typically what happens is the driver starts spinning tires — your son driving may be a clue here. Spinning the tires causes the side and pinion gears inside the differential to spin twice as fast as the tire and the lubricating oil can’t get to them fast enough to prevent them from scoring the shaft they are mounted on. When the pinion shaft scores, it often breaks its securing bolt and the shaft then works its way out of the differential unit. Eventually the shaft works out far enough to hit the transmission case and punch a hole in it. The result is an oil leak, loud noises from the transmission and sometimes the car is unable to drive.

The fix for this is a new transmission case and differential unit and gears, but this is very expensive if you can find the parts at all. You would be better off financially trying to find a used transmission at a salvage yard, but these are becoming harder to find. The other option is to sell the car “as is” and look for another vehicle.

Jim Kerr is an experienced mechanic, instructor and member of the Automobile Journalists’ Association of Canada.