Chevy & GMC Vans

WOW! Thanks! Didn't mean to sound ungrateful by starting another post...just did it to have a more specific title and possible attract more attention...so thanks for the merge Dean.

As of now, I think I'll be sending by ECM back to Dave at Command Performance Engineering (Denver) to "mask" the bank 1 sensor 2...which the computer thinks I have, but which is not the case.

I'll do my best to check what I can from that info regarding the low voltage. Could be exhaust or pigtale given the tranny swap I did months back. The code didn't come up til recently, but that doesn't mean things didn't progress. I'll get more detailed once the ECM comes back...may need some more advice at that point.

Also, Dave (CPE) mentioned the O2 connectors are holes 22 and 26 on the Blue connector for both V8 and V6, but that the V6 has a common ground for the downstream sensor (called Bank 1 sensor 3), located in hole 12 of Black connector on ECM. He wonders if cutting this will drop the low voltage code. I did not do it, cuz it doesnt feel quite right....but...any thoughts?

Gabe,

As a general rule of thumb - cutting wires to repair a problem is not really a repair. However, we are dealing with an unusual vehicle here, right? That being said, I do not see that cutting the tan/white wire at terminal 12 of the black connector will resolve the issue.
I would focus my attention on the purple/white wire to terminal 22 for a rubbed or burned area to ground.

My thoughts as well. In terms of hole 22, I've already checked for continuity from that and 26...to the matching pins on the female plug down at the downstream O2 sensor and they both read Zero. Should be fine in terms of ground, right? Do you know which pins match up to the the bank 1,2 sensors 1...the upstreamers? I believe my code doesnt have anything to do with those, but it'd be good to know/check anyway.

thanks!

I would not expect there to be a problem with the continuity of the wire in terminal 22. If there was, I would expect a high voltage code. You need to look for a problem of that wire going to ground - it should not have any continuity to ground when both ends are unplugged.
The same wire for the other sensors are terminal 19 - purple/white for bank 1 sensor 1 and terminal 21 - purple for bank 2 sensor 1.

Thanks! I feel a bit silly, but electrics are fairly new to me...HOW to I check for ground with both ends unplugged?

Oh, and once I send my ECM to Dave (CPE), I assume he masks the Bank1S2. Anything else you can think of he should do? He already is going to adjust the speedo etc 10%, because that is how far off it reads despite programming for 3:73's and 31inch tires. The "governer" has also been reset to 150mph, though I'll never take it that far...I have pinned it at 100!

thanks again,
Gabe

Connect the black lead on your ohm meter to a good body ground. Connect the red lead to one end of the wire. Your meter should read "0". Now connect the red lead to the other end of the same wire. Your ohm meter should also read "0".

If his meter reads 0, he is grounded. He wants a very high reading or "O/L".

You are CORRECT, Dean. I don't know what I was thinking. Evidently brain dead.

What is "O/L"?
Do I test hole 22 with downstream O2S plugged in?
What should the meter read if not grounded?
Is Key Off Engine Off?

Would you guys mind a quick play by play for my slightly confused brain?!

thanks!!!

According to James, you need to unplug the wires at the PCM and the O2 sensor. Now you set your meter on the highest resistance (ohm) reading setting it has. If it has an auto range function that will be ok as well. Now take the black wire to a good body ground and the red wire to a wire in the harness plug you unplugged. You must read a very high number or O/L. If it reads a low number, you have a short to ground.

Gabe,

These guys are directing you correctly, follow the directions given.

Here is a little hint or tip on how to find intermittant shorts to ground. Disconnect both ends of the wire that you suspect is grounding. Connect the clip of a test light to battery power. Connect the 'tip' of the test light to the wire that you think is grounding intermittantly. Slowly move the harness around though its normal range of motion. If the test light comes on, that indicates a ground.
It is almost the same as using a multimeter, just a little better 'visually'. A multimeter is better for finding smaller resistance issues - less direct shorts. A test light is better for larger resistance issues - more direct shorts

Thank you much everyone. I keep meaning to get after it, but just moved from Berkeley to Marin county and....the DIY shed from home depo took me and my girl 10 friggen hours!! That was a big fat surprise!

Update:
I sent the ECM in for a masking. Dave at CPE switched off Bank 1 and 2 sensors 2, and switched on band 1 sensor 3 which is what our vans originally are supposed to have...or so he say from his manuals. So far no codes. I did notice that when looking at the O2 sensor selection on my OBD2 scantool, it only showed banks 1, 2 sensor 1. Not sure if this means he accidentally ran a total mask of downstream sensors. He certainly didnt mean to, because he knows I need to pass a referee station here in CA before getting smoged. Haven't yet talked to him about this new find.

Update 2....gotta send it back again because I just figured out that CA is quite strict and requires a near exact replication of the engine exhaust system...for the 5.7L this means I need 2 cats in roughly the same location as per the donor vehicle!

Had my exhaust redone and now have to add wires for a second downstream cat!! Friggen bull s*#t!!

Dave at CPE says he'll figure out which pins I need to add...anyone have suggestions until then?