Rear Wiper Problem

[ncphotographer]

I've noticed lately that my rear wiper is acting funny. Sometimes it starts working when the wiper switch is in the off position.....I have to turn it on then back off again to get it to stop working......and also regardless of what speed the wiper switch is on the wiper moves at the same speed. Any idea if this might be the wiper motor or maybe the wiper switch?

 

[The_Roadie]

The communication path for this function is pretty convoluted. The control switch is read by the Body Control Module (BCM) under the rear seat near the fuse block. Then it sends a data communication packet through the shared serial data bus to the Lift Gate Module (LGM) in the liftgate. Which sends a PWM (pulse width modulated) control signal to the wiper motor which varies its speed according to the control signal.

It's statistically most likely to be a problem localized to the wiper motor, but could be in any part of the path. Difficult to diagnose for certain without advanced electronic tools. You might end up shotgunning it, starting with the motor. A local buddy to trade parts with could save you a couple of bucks.

 

[IllogicTC]

The communication path for this function is pretty convoluted. The control switch is read by the Body Control Module (BCM) under the rear seat near the fuse block. Then it sends a data communication packet through the shared serial data bus to the Lift Gate Module (LGM) in the liftgate. Which sends a PWM (pulse width modulated) control signal to the wiper motor which varies its speed according to the control signal.

It's statistically most likely to be a problem localized to the wiper motor, but could be in any part of the path. Difficult to diagnose for certain without advanced electronic tools. You might end up shotgunning it, starting with the motor. A local buddy to trade parts with could save you a couple of bucks.

Correction: The LGM doesn't actually "send" a PWM signal in the common sense, meaning current flow TO the motor. Instead, the motor logic is provided with power, and has two grounds: One for the motor, and the other which is presented in a PWM manner by the LGM. So intermittent grounding of the wire may cause the wiper to believe it has received a signal.

 

[Matt]

In regards to speed of the wiper. It only wipes at the same speed, the 3 settings are for the delay... slow intermittent, medium intermittent and "normal".

 

[ncphotographer]

Thanks "The_Roadie" and "IllogicTC" for those very detailed explanations.......thanks "Matt" for your explanation......I didn't realize that.