Windshield Wiper Hidden Relay
I'm writing this post for two reasons. To help someone that has yet run into this issue, and to ask the question, How could I have used my scope on this diagnosis?
Customer complaint is windshield wipers will wipe one time when you start the vehicle or just turn the key on most of the time. A new GM wiper motor was installed as an attempt to correct the issue and then it was given to me. Looking through the GDS I did not find any codes in any of the modules. No bulletins or TSBs. Start looking through the data stream for wipers to see if any inputs are commanding the wipers on at key on, I noticed when I cycled the key the wiper relay command changed to active for a second and went off. That's the only PID I noticed changing at the time. Knowing that the motor was replaced with no fix, I popped the steering wheel cover off because it was easy and unplugged the wiper switch just in case it was sending a quick command. Problem did not change. Now that I know what fixed the issue I wish I would have went back to the PID list but instead I decided to check wires and see what is actually going on. Wires to wiper motor and fuse panel are easy access. I quickly learned that the wiper relays are internal on the circuit board inside the underhood fuse block. I had a gut feeling there was an issue with one of the relays. I did a voltage drop and load test on the wiper relay ground and also the wiper motor ground with good results. I verified the body module was in fact powering the relay for a second on the gray wire to the wiper relay. I move on to my park switch signal which is where I find my issue. When the wipers came down to a stop the park switch closed but then opened back up. Light bulb. I go back to my PID list and see the park switch signal. When the wipers come down to park the signal switched to active but switched back to inactive. I grabbed the wipers and as they came down I held it at bottom and the wipers parked and switch stayed closed. Key on and wipers did not move. Its a park problem. When you cycle the key the computer didn't see the wipers parked so it went ahead and swiped them once to attempt to park them. I continued to watch the wipers and when the park signal worked the wipers would come to a jolt stop and when it did not work the wipers would slowly come to a stop and then slightly budge and would open the park switch. Discussing it with my coworker we figured out that when its time to park, the yellow and brown wire grounds the wiper motor to stop and hold it. Well the relay was unable to do that the more we played with it. It was a weak ground. We decided tap in a external relay to help it out and it worked perfectly. I'm attaching how we wired the relay. Wipers parked every time, PID showed park active, and the problem was gone. I replace the fuse box which was updated and all is well.
It sounds like a lot but I spent less than 2 hours including install. I have had internal relay issues with plenty of Chrysler products but this was the first GM. Sorry for the long post but I had to explain how it unfolded. Yes I took the long way around by missing the Park signal PID. Better luck on the next one. Hope this helps someone because I'm sure this will happen again.
Why do you think a scope could have helped? It sounds to me like your test methods were correct. You Installed a relay to confirm your suspicion. I don't think a scope would have helped. And I am scope guy
Not saying it would. Just looking for more reasons to use my scope.
The scope would shown the same loss of signal that you observed. Would be redundant, but your diagnosis could have been done using either. Good job on figuring it out AND confirming correction.�
Great job and thanks for sharing.
Good stuff. On a side note, I would have been done after the extra relay, because they would have declined to fix it and I wouldn't want to spend the time removing it. .......On second thought....I never would have installed the relay, I would have held the ground with my hand and a jumper. :-)
I gave the customer the option to leave the external relay or install the new box. List price was just over $200 It was in stock and it was an updated box so they chose to replace it.
LOL. It sure is supposed to. (Hence the term "tropical island") However, this summer has been so unusually hot and dry that we have had several wildfires. You'd think we were in SoCal or something!
Just a note when I ran across anything weird (defined by no info or diag tree in manuals) I concentrated on the ground side 1st. Learn about load testing and volt drop testing ground circuits. One of my proudest (yea I did the look at me strut) when I found a problem with a BMW that had been to 3 dealerships for intermittent die and restart turned out to be a ground under the coil cover loose…