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Ok, this one has me stumped.
I have a 97 expy and the rear wiper wouldn’t work. I checked voltage at the connector and it showed 12.5v when the relay cycled. I replaced the motor. Wiper still wouldn’t work. Checked the switch, fuse and relay. All good. Got the wiring diagram. I found that the circuit is controlled by a GEM that sits on top of the interior fuse box. I researched that and discovered it’s a common failure item. I replaced it with a junkyard part that was tested good. Wiper started working but was not running strong. I had the fuse go out. Replaced fuse and checked continuity across all wires in the circuit and it was good. Worked another week and now it will not cycle. I’ve checked for shorts and grounding issues and have found none. I’ve got about 12 hours into this diagnostic and it is no closer to being solved. Anyone have any ideas?
Thanks
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Here is what I’m getting at the harness connection to the motor.
It’s a 4 pin connector
Pin 1- ground
Pin 2-11.76v
Pin 3-14v
Pin 4-14vMotor does not run. It’s a new unit from Napa
Looking at the service manual. it shows two relays. One to move the wiper arm up and one to move it down. Blk/Ltblue should have power when the wiper is moving down and the white/orange wire should have power when the motor is running in the up position. Black wire is ground all the time and the purple/yellow wire is your motor position/park sense circuit monitored by the GEM.
That’s what I have in my diagram from the FSM. I have the alternating 14v on the two lines that drive the motor. This is with the connector unplugged. I’m going to back probe the connector and see what happens. Do you have any idea what range of voltage the GEM is looking for? When I plug the connector back into the motor the relay cycles and I have 14v alternating at the power distribution box. I would assume the GEM is seeing the correct voltage because it continues to power the circuit.
Which brings up how does that position sensor circuit work? If the motor is unplugged shouldn’t it not power the drive circuits, seeing how the motor position is unknown?
I’m trying to come up with a way to test the entire circuit with load on the motor side and simulate the voltage the GEM is looking for to cycle the relays. That’s the only thing I can think to do at this point. I have a hard time blaming a new motor. I want to come up with a test to make sure that’s the problem before I return the part
Just by looking at the diagram it looks like the GEM sends out a Voltage of some sort not sure if it would be 12 or 5 volts and depending on where the switch is in the motor pulls the circuit to ground. Have you looked at the pins on the connector to make sure the terminals aren’t spread or burned. Also check the sense circuit at the GEM to make sure the signal is actually getting to the GEM.
Yep I’ve checked the pins at every connector to verify that they are making a good connection. So I’m guessing the motor position switch closes at the limit of the motor travel? The circuit must also have a timer, because it cycles independent of the switch. Unless the switch is for the non-operating storage position, where the blade moves off the window into the lock position. I would like to figure out the nature of that switch in the motor and what the on-off conditions are in the GEM. I tried checking the continuity of those two pins going into the motor and it is closed across it in the down position.
I will attempt to find the wire going into the GEM and check there also.
Maybe I just take the part back and exchange it for another one….But it just seems like something else is wrong which is causing motor failure.
Does this condemn the motor? The signal wire is being pulled to ground, confirmed by a continuity test.
Motor is not drawing any amps
Ok it’s the motor, I applied 12v to each side of the motor to get it to work and it’s dead.
This is the stuff that gets under my skin. A bad replacement part cost me a ton of time. It was the thing I suspected the least. Figured since it was new the problem was in some other part of the circuit. A simple motor test would have determined this from the beginning. I feel stupid
Glad you figured it out. Looks like you did your due diligence to work through the problem. Unfortunately I have seen many “NEW” parts cause problems right out of the box. Its a bunch of crap.
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