lidger

HI all!

I just purchased a 2015 Class C RV on a 4500 Express Chasiss and I am looking for some help/guidance with a power windows problem (Driver and Passenger)

I purchased the vehicle knowing the "power windows were in need of repair". I figured it would be easy enough. Buy a new switch and I'll be good to go. Nope....still no driver or passenger windows

So I purchased the new driver switch, which wasn't the issue. I then purchased a 25amp "relay" found under the driver seat, still no go.

I cleaned all the grounds I could see, which none of them had any visible corrosion and still "looked" ok. Nonetheless, I cleaned the connections and reconnected. Still no windows.

I don't have any diagrams to reference and I feel I exhausted the tips I found on this forum and elsewhere. I found info from a 2004 Express, would that share diagrams and schematics with the 2014?

Anyways, I appreciate any help or input you may have.

-L

mountainmanjoe

diagrams are on gmupfitter.com
I would get out the multimeter and start probing

lidger

Thank you @mountainmanjoe , I will take a look there to see what I can find.

pomerlo

Here is the schematics found on gmupfitter for your 2015: (thanks MMJoe)



First I would check if you have power at the Dark-Green wire at the driver switch. (Cycle your ignition switch first)
If not then a suspect would be the RAP relay,

Was wondering what a RAP relay was and this is what I found:
Retained accessory power (RAP) is a power mode that permits the operation of some accessories for up to 10 minutes after the ignition switch is turned OFF. The RAP power mode is enabled by the body control module (BCM).

The BCM:

- Controls certain body functions.
- Sends out a class 2 message via the serial data link, which enables/disables other modules at the beginning/end of the RAP power mode.
Some BCM features, such as the interior courtesy lamps will function after the 10 minute RAP time limit has elapsed. This is normal, and does not mean the RAP power mode is malfunctioning. The BCM enables the following functions in the RAP Power Mode:

- The windshield wipers and washer through the RAP/adaptive cruise control (ACC) relay.
- The right and left power windows through the RAP/ACC relay.
- Any class 2 module that functions in RAP power mode and is not connected to the RAP/ACC relay, is controlled by the BCM via class 2 power mode messages. EXAMPLE: The radio works in RAP power mode because the BCM sends it a class 2 message telling it that the power mode is RAP.

RAP is disabled when:
- A door is opened.
- Low battery voltage is detected by the BCM.
- The ignition switch transitions from OFF to ON or ACC.
- 10 minutes have elapsed after the ignition was turned OFF.

The BCM monitors the ignition switch position, battery voltage and passenger compartment door status to determine whether RAP power mode should be enabled. If the ignition switch transitions from ON to OFF, the battery voltage is within the acceptable range, and the passenger compartment doors are closed, the BCM enables RAP power mode. After 10 minutes have elapsed, the BCM sends a class 2 message to the serial data network. This message commands the other modules that are power moded by the BCM to stop functioning.

RAP/ACC Relay
The BCM controls the RAP/ACC relay coil circuit using low side drive. The output of the relay is used to supply battery voltage to the windshield wipers and power windows. The RAP/ACC relay also provides voltage to the windshield wipers and power windows when the Accessory and Run power modes are selected.

So probably a regular relay energized by the BCM. But I would check if these relays are the same as the others?
If the relay is not sending power via the Dark-Green wire then check volatge at the relay to make sure your dark-green wire is not cut along the way.
Also from the diagram we can see the passenger windows having its own feed ( Dark-Green) check if there is power there ?
If not then chances are the relay is faulty. You could use a jumper to temporarly apply voltage at the dark-green wire and confirm windows normal operation.

Good luck

mountainmanjoe

Thanks for posting the diagram.
That sounds like the relay he replaced.

As always, this underscores the importance of performing a proper diagnosis instead of guessing and throwing parts at a problem.

Use a multimeter to measure voltage. They cost bugger all these days. $10 at harbor freight for a basic one. Or use a 12v test lamp if you have one.
The quickest way to isolate the fault is to start at the outer end of the circuit first, and work backwards.
test at the motor, then at the switch, relays, fuses and so on

lidger

Thank you @pomerlo!

I really appreciate you taking the time to reply and post that schematic. After a few hours searching the web last night, I concluded that it could be the BCM itself. I really appreciate the troubleshooting steps you provided, this will help tremendously in proving things out, and it's just what I was looking for to take the next steps in diagnosing the problem!!
I will do some probing/measuring in the vehicle today and report back what I find!

Thank you again!

lidger

@pomerlo I verified zero volts on the DK.Green line going into the driver and passenger switch(s). I tried to probe the relay under the seat and was unable (I can when I take the seat out).
I injected 12v to the DK green line at the drivers switch, and BOTH windows are functional. (so switches prove working)
I do not see a fuse in either box (Under Hood/Under Seat) for Power Windows, and "CB2" looks like a relay (does that test for continuity just like a fuse?)
So what does this tell me? Bad BCM? My next step was going to be remove the seat unplug everything and look for any corrosion and clean. If that does not result in the windows working, then I need to find a BCM and a shop to flash it for me correct?

Thanks again!

mountainmanjoe

no. you don't just jump to buying the most expensive part. You will probably end up with the same problem, only $800 poorer.
Now you need to go upstream of the RAP relay (again consult the electrical upfitter manual). There has to be a fuse or circuit breaker (CB) somewhere. (yes just like your CB panel in your home. Treat it like a fuse )
Don't stop until you find 12V.

Additionally, you can't just assume the BCM is bad. Measure it first. Maybe it's working, and there's a fault in the wiring harness.

lidger

Thanks MMJ.

I was planning on your suggestion once I get the seat out, and CB2 tests just fine (power windows CB) when I pull it and measure it like a fuse.

I'll let you know what I find.

thanks again