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Issue: 04 Rear wiper motor stop working - wiper arm speed basically dropped off to nothing until it did work. Figured the shaft bushings were gummed / corroded up restricting the arm rotation but not the case after tearing it apart.
So I have the read the posts on read wiper motor not responding. With that I measured OK with 12V voltage at the motor connector, so I went with the assumption that the motor was done, or rather control board that is part of the motor assembly. I dissembled the motor and bi passed the board to check the motor which ran fine, so control board is was suspect issue, however not a replaceable part. Ordered a Re-Mfg motor and still no work.(cross boarder shop at Port Huron save big at $118 vs $340 cdn)
So, I still have 12V (orange & black lines) at the motor connector so no wire breaks suspect.
Since voltage present, no fuse concerns. No wiper relays for this set-up
Trying to understand how the LGM plays into this??
Does the liftgate have be closed for the wiper motor to run?
Ignition & wiper switch on, I should be measuring what voltage off the blue signal wiper connector wire? Currently zero read.
(not clear on the schematic)Assumed the signal switch wire originates from the dash speed control and goes into the LGM located on the tailgate, and then to the wiper motor? So I have either a signal wire between dash switch and LGM, or LGM issue? How to check LGM or as per my reading this is to challenging with basic tools / knowledge??:
Seems like a number of the members have struggled with this, so hopefully some help is available. I thinking I replaced the motor for no reason.
Assistance that can save me spending any more dollars is appreciated
Your basic misunderstanding comes from how the modules communicate. The blue wire is a communication wire like a USB or serial (RS232) wire from your keyboard or peripheral to the computer. While you're sending a message (stroking the keys) there will be little flashes of voltage on the wire, but most of the time it's sitting at zero volts.
So when you change the wiper speed control switch, it tells the BCM (under the rear seat) what your desired speed is. The BCM then sends a short message (much less than a second) on the blue wire to the LGM, which then stores the information until you change the speed.
The green wire going to the rear wiper motor control board from the LGM should have a PWM signal on it, which means it's high for a while, then ground for a while, and the percentage of time it's high varies with the desired speed. This high/low change is too fast to see with a meter, but the meter might successfully read the average DC voltage. Or you might see a reading on the AC scale. You really need an oscilloscope to see the waveform as it really is at high speed:
Okay so I checked the green signal line on DC to the wiper motor connector. Wiper motor switched to highest frequency with truck running. From green contact I received .14-.18 constant reading when grounded to lift gate latch hardware. When grounded to actual striker on the body that the gate locks too, I barely received any voltage reading .0? somethings. I would have expected same measurement as latch grounding.
On the LGM, there a two couplings that each have a green line which is hard to follow unless I peel away harness tape. Not sure which green leads to motor, I'm guessing middle coupling since the outer engaged / disengaged gate locks when upplugged. Assumed if I checked this wire same voltage reads expected (did not want poke holes into wire coatings unless necessary)
You noted higher voltage reading which is about what?
I assume the low voltage signal opens a switch on the motor board to start cranking?
You could always poke through the insulation with a needle to get a reading.
See what the green wire has on it when the switch is set to low speed. I never checked mine since I haven't had this failure, but sometimes the HIGHER speed results in a LOWER voltage on the PWM control wire.
The wiper motor is commanded on and off hundreds of times a second by the PWM signal, so it's not controlling a relay at all. The ratio of ON to OFF time on the control signal is what makes the motor change speed. More ON and less OFF makes it go faster.
Here's some more detail, mostly borrowed from the service manual:
The rear wiper motor is supplied battery positive voltage and ground. The LGM controls rear wiper motor operation through the rear window motor speed signal circuit (green wire). The rear window motor speed signal circuit is supplied a battery positive reference voltage by the rear window wiper motor module and is pulse width modulated to ground by the LGM. The duty cycle of the pulse width modulation determines the rear wiper motor operating mode. As the rear wiper speed is increased from OFF to 3, the speed signal circuit is pulsed more often to ground - this can be seen by the dimming of a test light connected between the speed circuit and ground (or a decrease in voltage on a multimeter set up to display RMS DC voltage) as you increase rear wiper speed.
The liftglass and liftgate ajar switches are inputs to the LGM and must be in an inactive state in order for rear wiper washer system operation to be enabled. When an ajar switch is active the LGM suspends wiper motor operation directly.
I was wondering about the door or glass ajar and if it did disable wiper action. Saturday I was trying to measure the voltage on the green wire however only getting .13 ish volts not matter what speed I was running at.
I'm going to try the light test and doors and windows fully closed and hopefully get some illumination with some dimming at higher wiper speed.
The single voltage (green wire) should be around what- fraction of a volt or up around 6 volt?
Thx - Hopefully I can to get to root of this problem.
The LGM and motor have to be connected to the signal wire in order for the circuit to behave properly, so make sure everything's connected when you're testing.
This means you'll either have to backprobe one of the connectors, or as roadie suggested, poke through the wire's insulation.
I don't know what the RMS voltages should be on the signal wire, but the service manual states that the circuit is pulled up to a battery positive reference by the motor, so in the OFF state, I'd guess it should be up around 12v.
Finally back to trying to diagnose this rear wiper motor.
with Rear gate and glass closed I checked the voltages with a meter.
With wiper detached, I checked at motor attach wire coupling:
Orange to black - 12v
Green to black - .01v @ wiper speed 1, .02v @ speed 2, .03v @ speed 3
So it looks like incremental voltage signals are being received which each speed change. Why does the motor not re-act to those signals. HMMMM!!!
In a effort to figure what green wire at the LGM feeds to the wiper motor, I sequentially pulled the 2 couplings from the LGM until I lost power at the motor coupling.
Middle coupling feeds the motor, and voltage feed on the green wire at the LGM has the same output as above.
Since the voltage increments are apparent with the speed switch changes I'm assuming the required single is being sent / received. Only other thought is if the voltage strength of the signal is to low???
What's the chance this re-furbed motor is a dud?
Beyond that I am stumped. Any ideas are appreciated.
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