wit2pz

What supplies power to the circuit? I've been fighting a gremlin for 2 weeks now. I thought I had it figured out yesterday after cleaning 4 grounding points under the hood, including under the battery, and the point in the drivers side rear wheel well. After all my work yesterday, I got everything connected back up (battery, grounds, stereo and HVAC unit) and the lights worked without fail.

Today, I plugged the EBCM back up and from that point on, the circuit seems to have lost power. I unplugged the EBCM again and after all I've done, the lights are out again. They came on ONCE when I left the key in the Run position (engine not on) while I was reassembling the tail lights and putting the license plate assembly back together. When I got in to start it, they turned off and haven't been back on.

Today I have done the list below to troubleshoot, although to no avail:

replaced the backup lamp switch
replaced the backup lamp relay
verified all fuses are good
I spent an hour ringing out the wires from the switch all the way back to the lamps. I even removed the tail lights and found and cleaned the splice pack inside. Scary moment when I took off the backup light assembly; I discovered a Black Widow spider camping out inside the rear fascia area! Bought some spray and got it, HOPEFULLY good enough to kill it! It staggered into a crevice before I verified it was dead... I guess we'll see!

Anyway, after taking out the backup light switch and verifying continuity, I put it back in and verified continuity all the way back to the lamp sockets with the shifter in Reverse, and open when it wasn't.

What I don't have is 12vdc power going back to the lamps when I put it in reverse. I took off the battery cables, cleaned the two positive terminals that supply 12v to the fuse/relay center under the hood.

I always know when it works because the green light on the rear view mirror turns on when I turn the key, but it hasn't done it since this afternoon. I blame it on the bad EBCM, but I can't figure out what happened to the circuit when I plugged the EBCM back in. I unplugged it again and the backup lights/ HVAC/ rear view mirror dimming still don't work.

Any ideas?
Mike

65GGvert

Do they come on when you press the unlock on the fob?

wit2pz

Lucky, I've been trying to figure out why the ECBM has any effect on the lights since last week. The first thing I noticed was that the lights would ONLY work when the yellow ABS warning light on the dash turned off. It would do it whether the car was moving, idling, or just with the key in the "run" position. I haven't figured out that relationship, but it would happen most of the time. If I turned the car off then back on, I couldn't get the ABS warning light to turn off no matter what I did.

This past Saturday, I spent all day troubleshooting the issue, trying the 'reflow solder' method on the ECBM. It never worked. I mounted the ECBM back on the car but never plugged it in. That's when I got the lights working with a new backup lamp switch. Everything worked fine until yesterday afternoon when I plugged the ECBM back up, then the backup lamps stopped working again.

wit2pz

Yes 65GGvert, they do work with the fob. Different circuit though, right?

wit2pz

Lucky, I never had the C1214 code. None of my codes pointed to the normal EBCM problems that are fixed by ABS Fixer, but I was getting the Service Traction Control/ ABS messages on the DIC.

At first, I thought the backup lights wouldn't work unless the ABS and TC/AH warning lights on the dash went off. Then I noticed that they would work when the ABS warning light went off, even if the TC/AH warning light stayed on.

I got codes, but not the C1214 code that most people get when they send it to ABS Fixer. My codes were:
10PCM: P0135H, P0155H, P1258H, P1571H, P1689H

28TCS: C1277H

40BCM: B0432H, B0502H, B0507H, B2482H, B2527H, B2528H, B2587H, B2587H, B2592H

58SDM: U1040H
60IPC: U1040H
A6SCM: B0851H, U1160H

B0RFA: C2105H, U100H, U1255H, U1064H, U1096H

I can solder with the best of them, so reflowing solder to cold joints on the relay was nothing. After putting the module back in, I got the same codes. I cleared the codes and the ones that came back are:
10PCM: P1571H, P1689H
28TCS: C1277
40BCM: B0432H
58SDM: U1040H
BORFA: U1064H

I unplugged the EBCM and took a several hours removing the battery, removing and thoroughly cleaning the ground points in the engine compartment, scraping build-up off the ground lugs and using a wire brush, removing each wheel and inspecting the ABS connectors on each hub, and replacing the backup light switch after over-torquing and breaking the one I had.

After reconnecting everything, I had the backup lights working like a champ! After several starts and stops, they never failed. I was happy! Then yesterday, I checked codes and saw 28TCS- NO COMM. I popped the hood and realized that I forgot to plug the connectors back into the EBCM. Soon as I did that and turned the car back on, everything looked good, but I still had the 28TCS NO COMM so I cleared all codes and restarted. That's when my backup lights stopped working again.

The rest of the day was spent disconnecting everything and checking the backup light switch and the wires from there back to the lamp sockets. At the end of the day, I verified no shorts in the wiring from the backup switch back to the sockets. I verified the circuit closes with the gear in Reverse and opens when it's not, but I have no power going to the lamps when in reverse and the key in the ON position.

65GGvert

Lucky, what's the purpose of that connection F9 from the backup lamp switch to the EBTCM on the wiring diagram? I've never noticed that before. Is that what tells the EBCM that the car is in reverse?

wit2pz

I noticed that on the schematic as well. Interestingly enough, the backup lights worked like a champ with the ECBM completely unplugged from Saturday 6:30pm till Sunday (yesterday) 5:00 pm, when I plugged the ECBM up... Damned Gremlins!!!

What do you think, Lucky?

65GGvert

The backup lamp circuit itself is very simple. 12v is supplied through fuse 21 to one side of the backup switch on the transmission. If the car is in reverse it closes that switch to supply the voltage to the lamps. Obviously the lamp ground and bulbs are good or the approach lamps wouldn't work.
If this was my car, I would use the following sequence. Forget about the EBCM for now. Measure for 12v on both sides of fuse 21 in the passenger footwell. If it's there, short across the two wire connector that you pull off the backup switch on the transmission. With the igniton on, the backup lamps should be on. If they are, but when connected back to the transmission they aren't, you've either got a bad backup switch or the transmission internal part is not pushing the ball on the switch in enough to activate it. If they don't come on when you short across the disconnected plug, you've probably got a broken wire between the fuse box and the backup switch or from there back. You can eliminate the wire from the fuse box to the backup switch by measuring for 12 v on one side of the connector on the backup switch. If it's there and shorting those two together doesn't get you lights, it's between the backup switch connector and the lamps. Note that the backup lamp relay is after the backup switch, so you could still be losing connection around that relay.

65GGvert

I agree, that's why I told him to verify 12 v on the fuse. If it's there, the b/u lamps should work. If not, then he needs to go the other way and fix where it comes from. And unless I'm misunderstanding, the b/u lamps are not working at all now.

wit2pz

Thanks for the insight, guys. I made note of the mirror working (indicated by green led) AND the HVAC system working or not working in concert with them. If the backup lamps don't work, the mirrors don't work, and the HVAC doesn't function. Any insight there?

I'll have to take a look at Bill Curley's ignition switch thread and get smart on that as well.

65GGvert

I must have missed something about the HVAC, I didn't read anything in the thread about that.

wit2pz

I probably left that detail out; the waters are murky enough as it is, but since Lucky mentioned the mirror powered from the same fuse, I'm curious to know if the HVAC panel is also in that loop.

I really appreciate you guys for your help on this.
Mike

cdkcorvette7

http://forums.corvetteforum.com/c5-t...ch-repair.html

wit2pz

I'm all over it! Thanks and I'll be sure to report back once I get it done.

Rick@RKT Performance

1) turn key to ON
2) check pin A for power at reverse switch (if yes, go to 3)
3) engage the shifter into reverse
4) check power at reverse bulb socket (if yes check ground)

BCM controls reverse lights and DRL when FOB is pressed and has nothing to do with reverse lights coming on when in reverse.

wit2pz

Lucky, 65GG, CDK, Bill Curlee, THANKS A MILLION!!!

You were spot on. I couldn't get to it before late last night; I leave for work before sun up and get home after sun down, so last night, I found my mini maglite and followed Bill Curlee's instructions for ignition switch removal and repair.

I used my corded dremel on the lowest speed to clean, grind down, and polish the pits on the contacts. Put it back together and went to bed at 3am. Got up this morning and put it in the car... Not only did the lights and HVAC work like a charm, but I was able to get ALL CODES CLEAR!

Took it to the shop and got my inspection done (finally!) and Perma-grin has returned to my face! I even blipped the gas a little and chirped the tires in 2nd, just to see the Traction Control message flash across the DIC!

Now I have to remove the EBCM again and seal it up with black hi-temp RTV. Thanks again guys!