BCM rear access ajar

[vonoretn]

Matt,

I'll know more this afternoon. I have a neighbor with an 03 Yukon that is giving the message for the right rear door when it is closed, and I told him I'd look at it. I suspect you are right based on your first hand evidence, and therefore the other website is wrong. I've just been trying to do my homework before I looked at my neighbor's Yukon. Before I tear the door apart, should I check for one closed circuit with all the doors closed at that purple connector going into the BCM, on the wire side?

I already successfully fixed his speedometer by soldering in a new speedo stepper motor. Parts cost: $11.

 

[03YukonNH]

Ya don't pull the door apart. Just unplug connector C6 under the steering column. It is the only harness plugged in the the BCM on the rear side of the BCM. I am pretty sure it is purple.

The right rear door is the light green/black wire. Put the positive probe of a multimeter on the light green/black wire and the negative to ground. Open and close the right rear door and look for open and closed circuit reading on the multimeter (you will see 0 for closed circuit and O/L for open circuit in ohmeter function).

 

[vonoretn]

Matt,

Here is a surprise result for me. Baseline was you start the engine, and it says the rear hatch is open when it's not. When you put it in drive or reverse, it says right rear door ajar. I disconnected the purple connector to the black box above the brake, I assume that's the BCM? (Body Control Module?) And it makes no difference. Says the same thing.

 

[03YukonNH]

Matt,

Here is a surprise result for me. Baseline was you start the engine, and it says the rear hatch is open when it's not. When you put it in drive or reverse, it says right rear door ajar. I disconnected the purple connector to the black box above the brake, I assume that's the BCM? (Body Control Module?) And it makes no difference. Says the same thing.

Sounds like a BCM problem to me. You could take a chance and have the dealer re-flash the BCM and pay 1 hour of labor (approx $90) or buy a new BCM and still pay the dealer to reflash.

Just to make sure, though, have you tried probing the wires at the bcm when you open and close the doors/gate? The rear gate wire is pink/black. All the rear gate latches (2 for the liftgate and 1 for the hatch) are all paralleled up and ride on the single pink/black wire back to the BCM.

 

[vonoretn]

UPDATE #2: Let me retract my previous post. About a month after my supposed fix, the dreaded rear access ajar message started again. A simple knock/rap on the BCM would solve the problem but this was quite annoying. I finally broke down and bought a used BCM on ebay for $50. I went to the dealer witht he BCM and they installed and reprogrammed it for $90. So I am into this problem for about 5 hours of my time and $140. It has been about a week and I have had no problems so far. I will keep you all updated if it comes back or stays away.

Matt,

I know this is an old post by you, but I am wondering if you tried just replacing your old BCM with the used one you bought, before you had it reprogrammed.
A $50 fix makes sense, a $140 fix, not so much.

Also, is there any chance that disconnecting the battery or with battery disconnected, connect black to red wires to short out all capacitors/memory would help? I haven't done either yet.

 

[03YukonNH]

Matt,

I know this is an old post by you, but I am wondering if you tried just replacing your old BCM with the used one you bought, before you had it reprogrammed.
A $50 fix makes sense, a $140 fix, not so much.

Yes I tried the BCM I purchased first just to see what would happen but all the security lights came on and the truck wouldn't start. It cranked but did not start. I put my old BCM in and the truck started right up. This is what brought me into the dealer. However, I remember reading somewhere about a security relearn where you leave the key in the ON position for 10 minutes and then turn off and repeat three or four times. Not sure if this works for a new BCM but I guess its worth a try.

 

[vonoretn]

Matt,
New result, per your recommendation I measured ohm's on BCM entry green/black and pink/black wires, opening and shutting the right rear door and the rear hatch, and they both worked, the circuit closed when they opened and opened when they shut. Thus there is nothing wrong the door sensors, it must be the BCM. I will have the Yukon owner, my neighbor see if he can cut some kind of deal with the dealer to get the BCM reprogrammed for under $90.

Thanks for your sharing of experiences and expertise.

 

[03YukonNH]

Matt,
New result, per your recommendation I measured ohm's on BCM entry green/black and pink/black wires, opening and shutting the right rear door and the rear hatch, and they both worked, the circuit closed when they opened and opened when they shut. Thus there is nothing wrong the door sensors, it must be the BCM. I will have the Yukon owner, my neighbor see if he can cut some kind of deal with the dealer to get the BCM reprogrammed for under $90.

Thanks for your sharing of experiences and expertise.

I'm glad you were able to diagnose where the problem actually lies. I would agree that the BCM is the problem. The only thing I would be nervous about is having the dealer re-flash the BCM. The BCM more than likely has a hardware problem or short across the copper trace in the circuit board for the door ajar circuit. A reflash will not help this but then again I could be wrong. I'm not too familiar on what causes the BCM to act screwy.

 

[vonoretn]

I'm glad you were able to diagnose where the problem actually lies. I would agree that the BCM is the problem. The only thing I would be nervous about is having the dealer re-flash the BCM. The BCM more than likely has a hardware problem or short across the copper trace in the circuit board for the door ajar circuit. A reflash will not help this but then again I could be wrong. I'm not too familiar on what causes the BCM to act screwy.

Yeah, occasionally I have found a short or open spot on a circuit board, but all too often it is a failed chip which could be composed of dozens to thousands of micro-transistor, diodes, etc, and their is no fixing a chip, only chip or board replacement. In most cases, chips raise our standard of living (cell phones, computers, I-pads, etc.) but a failed chip is always expensive and economically unrepairable. If my neighbor allows me to, I might open the BCM module, and review it with a magnifying lens for a burn't spot or copper path short or break, but from my experience, it's only a 20% success possibility. If I do I'll post a picture of the circuit for others to observe.

Here is supposedly a brand new one on ebay:

http://tiny.cc/345nv

for $150. It says a new one would cost $403. I haven't confirmed that this part number would work, probably would not, since manufacturers change these things on a frequent basis to avoid depth should a recall occur.

 

[03YukonNH]

Yeah, occasionally I have found a short or open spot on a circuit board, but all too often it is a failed chip which could be composed of dozens to thousands of micro-transistor, diodes, etc, and their is no fixing a chip, only chip or board replacement. In most cases, chips raise our standard of living (cell phones, computers, I-pads, etc.) but a failed chip is always expensive and economically unrepairable. If my neighbor allows me to, I might open the BCM module, and review it with a magnifying lens for a burn't spot or copper path short or break, but from my experience, it's only a 20% success possibility. If I do I'll post a picture of the circuit for others to observe.

Here is supposedly a brand new one on ebay:

http://tiny.cc/345nv

for $150. It says a new one would cost $403. I haven't confirmed that this part number would work, probably would not, since manufacturers change these things on a frequent basis to avoid depth should a recall occur.

There is a number on a white sticker on the case for the BCM. As long as the BCM matches the number for the BCM on ebay then you are OK. I agree that more likely than not the chip will probably be the culprit and at that point you will be replacing the BCM anyway.

As part of my experience I opened up the BCM and went over the whole circuit for the rear access gate and probed all the resistors and checked for any burnt spots or corrosion and couldn't find anything.