Spartan7

iTrader: (7)

Apologies in advance, this will be a long post. But I've tried nearly everything I can think of and can't get rid of this code.

P0443 - EVAP Purge Solenoid Control Circuit

This is for my 97 T/A. Engine mods shouldn't really matter here, but if there's a slight chance of it causing something, I do have a cam. OBD2 tune, all emissions equipment is in place; high flow cats, all O2's operational, EGR in place, AIR removed (not a concern right now).

This all began a few years ago when I originally swapped the stock engine for the one out of a modified 96 Z28. I had a fresh tune done by PCMforless, which I was very unhappy with. That aside, I've had the issue since the first turn of the key with that tune. I also have a P1657 (CAGS) light which occured the same time as P0443. I changed no wiring, and had no SES lights at all before the engine swap.

I have recently had a good tune done by Moe (MoeHorsepower). He was not able to make the lights go away. However, I am planning on having him take another look at the tune soon to see if he missed anything. In the meantime, I've tried nearly everything I could think of to fix this light.

I had an extra OBD2 PCM lying around, so I had Moe flash it with the same tune just in case I had a bad driver on the old one. A PCM swap made no difference. The car runs perfect except for these lights. However, I'm not sure if this PCM was originally an A4 and if Moe re-flashed it or not, or if that even makes a difference.

This code is for an electrical fault, not for EVAP flow. That said, if anyone has had an issue of this code popping up for flow-related issues, I'm all ears. Every part of the EVAP system is in place (charcoal canister, all lines, EVAP solenoid, EVAP vacuum switch, etc).

I have traced every inch of wiring for this circuit. The wire is in the correct slot on the PCM connector (BLUE/C4 pin #10). I have ohmed out the wire, nearly 0. The brown wire has 12v in ignition RUN. The scanner I have does show the PCM is commanding the solenoid to open (percentage rises under load). I have replaced the solenoid 3 times, no change any time. Unplugging the solenoid changes no characteristics. If I clear the code, it takes a couple ignition cycles for it to come back, but it comes back every time I do something.

I have run my own wire from C4 pin 10 straight to the battery ground post, no change. I don't have a good scanner to actually command the solenoid on or off, so I can't test it that way. Since the wiring appears completely fine, there are only a couple things I feel are left; PCM, tune, or bad (yet again) solenoid.

This is with two different PCM's, and I highly doubt they would both have the same bad drivers (P0443 and P1657).

I have used an AC Delco solenoid from Rock Auto (which turned out to be a POS and was bad out of the box), a Duralast parts store solenoid, and a used GM one off my extra paperweight engine.

Does anyone have any input or has had a similar experience? I'm at my wits end with this thing, I can't get it inspected, and the light is driving me nuts.

Spartan7

iTrader: (7)

I thought I would update this with more info, for any that may have similar issues.

I found this video that was very helpful in diagnosing the EVAP purge solenoid.


I had already checked most of what he mentioned, but it was helpful nonetheless. Without a Tech 2, it is difficult to fully test the PCM driver and rule it out as suspect.

What I did to test it myself without a Tech 2 is to completely bypass the engine harness. I used a spare PCM connector I had laying around and took a pin out of it. I removed the engine harness pin (Blue connector, pin #10, dk green/white wire) and inserted my own pin. I then spliced wire onto it and used another spare purge solenoid connector I had to make a circuit, routing the purge solenoid inside the car. Run the other side to your fuse block for 12v.

This allowed me to actually hear the solenoid clicking on/off as it was modulated by the PCM, if in fact the PCM was good and doing its job. As the video below shows, the PCM is in fact working properly. Of course, the code is still present, which makes me 99% sure it's the tune.

https://www.youtube.com/watch?v=a0wN...ature=youtu.be

Kevin97ss

The PCM is looking for voltages on the green/white wire. It should be around battery voltage when no command for the purge is requested and near zero volts when its commanded on. With the key on engine off check to see if the G/W wire has battery voltage at the PCM pin with the purge sol. connected by using a test light(connected to ground), this will load the circuit to make sure it will actually flow current. If good, tap the G/W wire and run a wire inside the car, hook it up to a digital volt meter lead and the other lead to ground. Drive the car and have a passenger(for safety reasons) read the meter, if the PCM is functioning the voltage should switch B+ to near zero while at cruising @55mph.

Kevin97ss

Ok, read your second post and watched your vid...lol, should have done that first. The fact that the purge works tell me the PCM and tune are good, but you still need to find out what the voltage is on the G/W wire. The voltages there are how the PCM determines weather or not there is a circuit issue, hence the DTC.

Spartan7

iTrader: (7)

Yes, I know fully well that it looks for a voltage drop across the coil when commanded to determine if it's working properly. Whether proper voltage is present on the dk grn/wht wire (which it is) and whether it's dropping when commanded on (nearly impossible to tell without a tech 2) is irrelevant. I already bypassed all that wiring, mine is coming straight off the PCM and fuse block, yet the code remains.

Since I've proven the driver is good, the only issues can be a faulty voltage sensing circuit within the PCM (which I've been told is highly unlikely with a functioning driver) or the tune doing something to keep the light coming on. And since this issue started immediately after I had PCM For Less do the tune, I'm confident that's the problem.

Kevin97ss

Find out if its possible to adjust the DTC threshold voltage during a typical tune, I would guess no but in your case it seems that is what has happened. It may have been accidental or a corrupt file.

ChevyOwner

I see that you essentially wired a new evap circuit in place of the existing circuit and used a different purge solenoid to test the driver. This will tell you if the driver is good but after hooking the old purge circuit the problem may still exist.

It is really very easy to check the voltage on the dark green/white wire to watch if the voltage drops and how (without a tech 2). You simply connect a multimeter into that circuit so that both the multimeter and the pcm see the voltage from the solenoid.

It is not irrelevant to check that as from what I have read you removed your bypass wiring and hooked up the old wiring and solenoid that caused the problem. If this is incorrect then I misunderstood something.

Another possibility is that this code needs to be cleared for the light to turn off. You have not said if you have been clearing the codes.

Spartan7

iTrader: (7)

UPDATE: It's fixed! I recently acquired a copy of Jet DST (OBD2 tuner). Lo and behold, they were never disabled in the tune. A couple quick clicks, and now P0443 and P1657 are gone.

I hope this helps someone else, because it sure gave me a headache.