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So everything looks good around the connector. I followed it into the trunk, then loose the wires when they go down somewhere behind the rear seats and join up with some other wires. I checked out x200 last night, and all looked fine there. I also checked out the fuse panel, and the same. The wires are a little tight going down in there behind the seats so I'd like to see what's going on in there but I can't find them. Maybe above the gas tank.
I'm assuming the driver test has to be done at the pcm since a short to ground somewhere in the circuit would mess with the power probe results if it's done at the connector. When I tried this the green light did not com on.
I can see that someone has been in here before messing around, which probably isn't good. The main harness up front is brittle as hell too.
I think I'm going to run a new wire from the pcm to the valve to see if it actives the valve bi-directionally. If it does then the driver works and there is def a short to ground somewhere. I assume that would not be an acceptable repair since it would totally screw the next person to work on this if it's not routed the same way or even the same color wire.
Or I could cut the white wire close to the pcm and put a test light between that wire and b+ and see if it lights.
The other problem with running a new wire is what if that wire isn't the only one damaged? It just may be the only one causing a problem right now, another could start causing a problem sooner rather than later
I'm not really sure what to think of these results. I just backprobed pin 61 on the PCM, put a test light between there and B+ and got no shine when I forced on the vent. When I check for voltage there with my meter, I have 12v again with the vent on and off. Same results as I had at the connector at the other end of the car. Also have voltage drop there too.
I even cut the white wire near the PCM and did all of these tests and got the same results.
Have you cleared the codes? If not, clear the code then cycle the key off and back on with the vent unplugged. Then check your driver. I've seen driver's shut down when the vent is shorted. Then it comes back after clearing codes with the vent unplugged
12v comes from the fuse through the solenoid and goes all the way to the pcm. When you command the vent on and you still have 12v at the pcm either the driver in the pcm is bad or it had been shutdown to protect the pcm because the vent is shorted internally or the control wire is shorted to voltage
EricGoodrich wrote: B+ to 61 with vent commanded on and your test light doesn't illuminate means the driver is not operational.
I have seen internally shorted solenoids ruin drivers.
Ok thanks. Why would there be 12v there with it on and off too?
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In this case, there are two main loads in the circuit; The vent solenoid and the open transistor in the ECM. Since multiple loads in a circuit will drop voltage in direct proportion to their resistance, the open driver in the ECM drops a million times the volts as the vent solenoid. This is why you see battery voltage on both sides of the vent solenoid.
Close the driver and it is no longer a resistor. Now, for practical purposes, the vent solenoid is the only load in the circuit and it drops all the voltage, operates and will show battery voltage on one side and ground on the other.
Tutti57 wrote: Ok, I think I'm following. I was thinking the transistor would not necessarily be high resistance, but open, until it grounds.
Just when I thought I was starting to get it!
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An open in a circuit is high resistance because everything is a complete circuit, even an open circuit. For example, imagine a simple circuit with a light bulb and an on/off switch. When you open the switch you aren't actually opening the circuit, you are adding a section of air into the circuit. That air is a conductor and has resistance. Though, a very poor conductor and very high resistance, it is a conductor and has a resistance value, none the less. The available voltage in this circuit is now shared between the two main loads; the light bulb and the air. The light bulb drops very little voltage because the air in the circuit has such high resistance that it drops nearly all the voltage. That's why you'll measure battery voltage across an open switch and why you'll get no voltage drop across the light bulb.
Well thanks everyone for taking the time to explain that to me. I'll do some reading on it as well and find the videos that correspond with the chapters in Paul's book, so it sinks in deeply.
The air box seems like an odd place for the PCU. I'm assuming a used one would need to be programmed by the dealer?
Monde wrote: Great suggestion, Bruce. Titu57, let us know how the intentional shut-down driver test went.
No good. I disconnected the battery while I was messing with the pcm, so there were no codes stored. I connected the valve back up for the heck of it and still couldn't get my light to shine.
Monde wrote: How about providing a ground (being the computer) to the vent valve by connecting a test light to battery ground and touching pin 61 and see if you are getting 0 v at the connector?
I can try that too. Thanks
I bench tested the old valve and it wasn't doing much. The new one is working on the bench nicely, just not nicely in the car yet!
Monde wrote: How about providing a ground (being the computer) to the vent valve by connecting a test light to battery ground and touching pin 61 and see if you are getting 0 v at the connector?
Did you mean touching a power source instead of pin 61 since that is supposed to be a ground in this case? Just trying to make sure I understand all of this.
I would think that I would be able to plug the valve in and ground the white wire to the chassis to make it work. I'm not sure if using a test light here would provide enough power to shine the light and power the solenoid.
Monde wrote: Remember the pcm provides the vent valve a ground. When you put the test light to battery ground or any good ground point and touch pin 61, you provide it the ground that it needs.Therefore, if the wiring is good, you should get 0 v at the connector. If it does not work, you can use your dvom or a power probe to provide it the ground. If you put the test light to a power source, you are testing the power source. If you ground the white wire to the chassis, you short the white wire to ground. I don't think it is the right thing to do.
Oh, I see what you mean. Leave the vent on the car and ground the white wire to pin 61. Thanks for explaining it. Hope I didn't sound like a creep there.
Monde wrote: Remember the pcm provides the vent valve a ground. When you put the test light to battery ground or any good ground point and touch pin 61, you provide it the ground that it needs.Therefore, if the wiring is good, you should get 0 v at the connector. If it does not work, you can use your dvom or a power probe to provide it the ground. If you put the test light to a power source, you are testing the power source. If you ground the white wire to the chassis, you short the white wire to ground. I don't think it is the right thing to do.
Yup, i hear it clicking back there when I ground pin 61. Good test. Thanks.
I finally got this one back in to finish up. I ordered a pre-programed PCM from a place I found on eBay. No core requirement for GM models. You give them the vehicle info like the VIN and they ship you a module for $75. Turn around was like a week and they advertise it to be sooner, but the price is right.
I installed the new unit, performed a key relearn, crank relearn, and it's good to go.
Thanks for all of your help here. That was a fun one.
