2003 SSEI - Rear Defrost

[Rhodizzle]

Hey folks,

I've been having a hard time searching for what to check to troubleshoot my rear defroster not working. When I hit the button on the dash, it lights up but I get no defrost.

Ideas?

[96 SSEi]

fuse and possibly relay in the rear block under seat......do the wires on the window look good? are any damaged?

[ddalder]

When you press the button for rear defrost, the HVAC module sends a class 2 serial data message to the Rear Integration Module requesting it to activate the defrost grid. Once the RIM engages the relay, it sends a message back to the HVAC control instructing it to turn on the indicator lamp. In short, it seems the most complex part of this is working.

Fuse #61 in the rear fuse block, which is one of the physically large fuses (rated at 40A) is for the rear defrost. Relay #59 which also happens to be one of the physically larger relays controls it. As mentioned, check the fuse. Do you hear a relay click under the rear seat when you activate it?

If the fuse is okay, try swapping the two mini-relays (the large ones, all others are micro relays) and see what happens. There are only two in the rear fuse block and the other one is used to provide power for the cigarette outlets so nothing crazy is going to happen by removing it.

Finally, you may need to remove the 'C' pillar trim to visualize the connections to the grid. Wires are soldered to a wide braid which is held to the glass with an adhesive. You'll want to make sure everything along the two extreme edges of the rear glass is secure. This is slightly different than some other vehicles that have a connector block attached to the glass and a wire that plugs onto it. Our system seems to be more robust. Sometimes the connector block used in other systems has a tendency to separate from the glass.

[Rhodizzle]

Thanks DDalder, I'll chase that down and post back.

[Rhodizzle]

8 months later...

I finally got around to doing some testing.

-The 40A fuse in position 61 is good.
-The relay clicks on when I turn on the rear defrost.
-Just for fun, I did some testing with a multimeter. I'm getting continuity from the positive battery terminal to the fuse, from the fuse to the relay as well as from the relay up to the driver's side connection with the rear window (inside the C-pillar). I also tested from the passenger solder point on the window to the ground bolt behind the C-Pillar.
-With the fuse and relay replaced, I am getting 12V from the driver's side of the window to the negative side of the battery.

Anything else to check? It seems like it should be working perfectly fine. With it being warm out right now, I'm not sure how to test that the window is actually heating.

[ddalder]

Hopefully nobody damaged the grid lines by scraping something on the inside of the glass. It sounds like you've been quite thorough in your testing. You could try unplugging the connector on the driver's side (2 cavity with the black and purple wires), then measure the resistance from GND to the braid on the driver's side glass where the purple wire is soldered. Is the glass tinted?

[Rhodizzle]

No Tint.

I'm reading up on how to do resistance testing on a defrosting grid. I guess you have to go through and test each line in the grid to find the gap. They make kits to repair it, this one for example.

I'll let you know how it goes...

[ddalder]

They definitely make repair kits, but I was under the impression that none of the lines work. It would be incredibly unusual for the entire grid to be open unless it was damaged. Just to confirm, did you measure the voltage on either side of the grid where the wires solder on?

[Rhodizzle]

Correct, none of the lines appear to work.

Is anyone able to pull their C-pillars and snap some pictures of the connections on both sides? I'm trying to figure out if something is missing...I see two solder points on the right and only a single on the left.

Edit: I was able to find this parts diagram that shows the connections. The harness on the driver's side connects to both ground and the relay and the one on the passenger's side just connects to ground. I'll have to get back in there and test the grid itself next.

-Rhodizzle

[ddalder]

That is correct. There should be a purple and black on the left side and black on the right. What voltage do you measure at the solder connections? Sometimes the pad has been known to separate from the glass. You can give them a gentle tug but I wouldn't pull exceptionally hard.

[ddalder]

Also, disconnect the connector on each side and check the terminals. If they did not make a solid connection, the current required over time could have caused a poor connection.

[Rhodizzle]

That is correct. There should be a purple and black on the left side and black on the right. What voltage do you measure at the solder connections? Sometimes the pad has been known to separate from the glass. You can give them a gentle tug but I wouldn't pull exceptionally hard.

I tested from the left side to battery ground and got 12V with the defroster turned on. I need to recheck that though. The two wires are on the driver's side and the single wire is on the passenger's side. Will check connectors as well.

[ddalder]

Correct. Driver's side is left.

[ddalder]

Assuming there is power to the grid, once you have checked the connectors, etc...

To find a break in grid lines, gently pass some steel wool along the length of each line with the defrost turned on. If you see sparking, that's where the break is. Sparking occurs when the steel wool completes the circuit. Don't press hard because you don't want to damage the trace.

[MKMike]

Assuming there is power to the grid, once you have checked the connectors, etc...

To find a break in grid lines, gently pass some steel wool along the length of each line with the defrost turned on. If you see sparking, that's where the break is. Sparking occurs when the steel wool completes the circuit. Don't press hard because you don't want to damage the trace.

That's a great tip!

I'll have to remember this one.
Thanks for sharing it.

[ddalder]

Fine steel wool (00) twisted to a point is probably best. The down side is that if there are two or more breaks in the same trace, this method won't work. If this is the case, the only real way to find the breaks is with close visualization using a magnifying glass.

Using super fine (0000) steel wool typically used for polishing chrome is probably a bad idea. I've read on product packaging that even improper storage/handling can cause it to catch fire. I never would have thought steel wool was flammable but I guess it is.

[MKMike]

Good to know.
Wouldn't want to find the short and ignite the car at the same time!

[ddalder]

Good to know.
Wouldn't want to find the short and ignite the car at the same time!

Yup, that would be extremely counter-productive!