I'm starting to see if I put p0443 everyone looks at it but no answers. My truck has this code and OD light blinking also. If I unplug the purge valve the OD light stops immediately. Transmission is fine purge valve is new (motorcraft) and it works. For some reason my computer thinks my transmission is overheating first thing in the morning and my purge valve is not working. I have check the harness and replaced the ecm/pcm with no results. I have seen this problem on many threads f-150 and Bronco. Does any one have an idea? If not I promise to stop asking.
(Why did I sell my '79 F-150?)
Thanks,
Mike

 

How do you know that? You must be getting other codes so forget about that emissions code since it has absolutely nothing to do with your transmission and tell us what other codes your computer is flashing at you.

 

I am only getting 2 codes the p0443 (evap purge valve fault) and a p0713 ( trans fluid temp). I had the transmission flushed and they said it was in great condition. They also plugged in a new solenoid pack and the ecm/pcm still said the the trans was overheating. When I tried a rebuilt ecm/pcm I got the same codes.

 

For some reason my computer thinks my transmission is overheating first thing in the morning

All the time or only in the morning?

When you say I have check the harness what did you do, what have you done exactly?

Hot trans fluid = low resistance, cold trans fluid = high resistance through tot sensor.

If not just in the morning, reads hot all the time perhaps Pin #42 (TOT) and pin #46 (SIG RTN) are shorting out to one another at some point by passing tot sensor entirely?

 

Thanks for the input DANR1.
The transmission OD blinks all the time.(if my purge valve is pluged in) I was just pointing out that even with the transmission cold the computer thinks it's overheating.
If I disconnect the purge valve the OD flashing never comes on.
I have followed the key on ,keyoff check list that is always mentioned on this site.
It always comes to the last yes or no "replace computer".
My transmission shop check the harness to the transmission.
I also checked pin to pin on the ecm/pcm plug.
I'm at work right now but will try your steps when I get home.

Thanks

 

The voltage supply for the Vapor Management Valve (VMV) comes from the load side of the EEC (PCM) relay. That same supply feeds a bunch of other circuits. I bet you have another component pulling a lot of current or a high resistance short to ground in the wiring.

Some other items on the same circuit: Fuel Pump Relay, Mass Airflow sensor, fuel injectors, IAC, EGR Solenoid (EVR), O2 sensors, etc. I wonder what would happen if you unplugged the EVR if the O/D blinking goes out? Meaning I think unplugging the VMV is removing enough of a load for the circuit to work? By removing something else would the symptoms change accordingly.

 

Do you think the wiring diagrams in a Chilton or Haynes shows enough detail to trace down the other components. If not do you have a good resource that I can look up to find a real schematic.

Thanks

 

I use a Haynes, its adequate to the task.

I'd also do as rla2005 suggests, very good suggestion, makes lot of sense and very well might just give you ammo looking for in search of the problem.

Hitting on the right sensor, unplug the one creating the problem would at the same time allow TOT to function as it should too.

That brings up another question (without taking minute review), when you unplug the purge valve, without it connected does the tot read normal?

 

I have not checked the tot with it disconnected. I thought since the od blinking stopped when I unplugged the vmv my problem was some where else. I will unplug the circuits one at a time starting with the egr solinoid that rla2005 suggested. Unfortunately a lot of those circuits cannot be disconnected and still run, right?

 

Unplugging the EVR will trigger another code, but the truck will run. Same for the O2 sensors.

 

Had to work today and have to go to B-day for friend right now but I did have time for the following.
I started the truck no OD blinking.(vmv unplugged)
I plugged in the vmv and the OD started to blink.
I unplugged the vmv and the blinking stopped.
Disconnected the egr control solenoid.(no blinking)
Reconnected the vmv and it started blinking.
I then did the same process for all three O2 sensors.
Mass air sensor.
IAC valve.
With the same results.
My diagram shows a "secondary air injection diverter" that I cannot find and don't think I have. I have no air injection pump or exhaust manifold tubes.
It seems like any time I plug the vmv in I'm going to get this code.
If I'm right the vmv does not even get a command unless the gas tanks are lower than 3/4 tank.
That is how I smogged it last year. Filled the tanks cleared the codes drove it to the smog station before the vmv got a purge command. Passed no problem but in California if the #@$% engine light is on they fail you.
Sorry for all the info just trying to be detailed.

 

Test the gry-yel wire for continuity to ground at the canister purge valve with the key "off", the motor idling and once more time with the Key in the "run" position engine not running.
Quick test get that one out of the way a minute.

Where the TAB and TAD solenoids removed? If so could have been and should have been left electrically active to fool the computer thinking air system was there and functioning as it should be, even though remainder of it had been removed.

If the solenoids had been removed make sure the connectors for them are not grounding out against anything just to be safe.

 

Test #1 Key off engine off. Continuity to ground.
Red= 1.108k ohms
Lt. Green/black= average 2.5m ohms

Test #2 Key on engine off. Continuity to ground.(or vdc)
Red= 11.82volts
Lt. Green/black= average 2.5m ohms

Test #3 Key on Engine Running. Continuity to ground.(or vdc)
Red= 14.50volts
Lt. Green/black= average 2.5m ohms

This truck never had air injection You can see where the TAB and TAD would clip in but no sensors or even plugs from the harness. I guess 1996 OBD2 California trucks did not have air injection.

If you all agree with me that the vmv does not even get a purge command until the tanks are 3/4 or less and after the engine warms up, then how would the hot wire pick up a drain when starting cold in the morning. Even when to vmv is disconnected the red 12volt is always constant and the lt green/black is not ground until the pcm gives the command.

Test #4 With the engine running vmv unplugged (OD not blinking) I used a test light on the vmv red 12volt so it act as a resistor and possibly cause the OD to start blinking, but it didn't. The second I plug the vmv in the OD blinks again. I tried this with my old vmv and my new (motorcraft) vmv. So when the vmv is plugged in the voltage some how is going thru the resistance in the vmv and going down the return (ground) wire to the computer?

I have checked that wire for continuity to the pcm plug and it checks out good. When I first discovered this all results pointed to the pcm. I put a rebuilt pcm in and my truck ran terrible and not only thru the same codes but many other codes I have never seen before. I shipped it back and they sent me a new on that ran alot better but blew the same weird codes. I'd have to look for those codes but they where left of right bank to lean codes I think. I returned that pcm also and I'm still using my factory pcm with no problems but the P0443 and OD blinking. The truck runs very well and always burns very clean at the smog tests. But here in California the check engine light is a automatic fail.

Not sure about TOT Pin#42 or #46 SIG RTN. My diagram shows Pin 37 on pcm to pin 7 (temp)on my E4OD plug and pin 91 from pcm to pin 8 (signal return)on my E4OD.

Feel free to correct me if I'm wrong about any of this.

 

Ok yours is OBDII and then EEC-V (100 pin) so pinouts are not same as what I have.

Yes key on power to VMV, computer provides path to ground to open it as required.

According to "strategies" canister purge doesn't occur until warm cruise and or under deceleration conditions.

Based on that you should not have continuity to ground on the computer side of the VMV with the key off, key on or with engine running sitting still and at an idle. Had read (IIRC) were one poster was successful in triggering canister purge by simply increasing idle speed truck not moving but don't recall exact conditions.

The fact you do strongly suggests a problem there in that circuit (should have shown "open"), especially when you consider you do even with the key shut "off".

I'd unplug the computer from the harness and run the same test on that circuit, should have no continuity to ground in that circuit computer disconnected (or connected). If you do suggest that wire is shorting out causing your issue, if you don't the computer itself might just be the problem.

Keep in mind I'm going out on a limb here just a tad as my book doesn't cover your system. Gotta believe it's same/similar in function as far at that aspect goes though.

 

Thanks danr1.
I disconnected the pcm from the harness and there was no continuity at all. So common sense tells me something is wrong with the computer but I have been down that road before. Was I that unlucky to get two POS rebuild pcms? Do you know of any good company's that back up their pcm. The one I dealt with finally gave me back some of my money after calling them about ten times. I would love for this to be the problem even if it cost $300 but I'm afraid there might be anther problem because the rebuilt pcms blew the same code and OD blinking. If you have time, with your pcm plugged in, check your continuity between the vmv ground side to your battery ground just to verify.(if your truck is close to mine) Is it open or 2m to 3m ohms? These are milli ohms right?