Torque

Forums

Forums

Guest  

Show or hide header
Welcome Guest, posting in this forum require registration.




Torque » Torque OBD ECU Scanner » Torque Discussion / Ideas » P0446 won't clear on 2003 Expy

Pages: [1]
Author Topic: P0446 won't clear on 2003 Expy
MechanicalFailure
Member
Posts: 2
Post P0446 won't clear on 2003 Expy
on: May 14, 2020 (GMT)

I am trying to find out how Torque can help me troubleshoot the issue. I do not have the fancy M$ scanners. But, I do have meters, O-scopes, and other tools I use everyday.

For Ford, P0446 is a circuit issue with the EVAP Vent solenoid. I have gone to great lengths to prove the Vent Solenoid, power, and wiring are all good.

The test that Ford has triggers “at some point”. I have not been able to capture that trigger with hardware. It is possible that the computer is bad. However, I want to diagnose further before resigning to that possibility.

Can Torque view, trigger, or expose anything that would help me diagnose further? The fancy scanners have the ability to enable/disable the solenoid. Can Torque at least show that the system executed the command to do so?

Also, on the off chance that I am totally wrong that the circuit is good, does anyone know what other criteria Torque can view that helps to troubleshoot this?

moreause
Member
Posts: 480
Post Re: P0446 won
on: May 14, 2020 (GMT)

get the forscan app
since it’s a ford you will have access to WAY MORE stuff
and if you have an obdlink MX or an adapter with a switch you have access to even more stuff

ford have a high speed bus for engine side and a medium speed bus for the interior stuff radio ect

and from what i read p0446 is not only the valve circuit
but the whole system

a leaky gaz cap, on any leak will trigger the code

Tux
Member
Posts: 8
Post Re: P0446 won
on: May 15, 2020 (GMT)

If you haven’t already, search for and download the 95-page Ford document “obdsm307.pdf” (“2003 MY OBD System Operation Summary for Gasoline Engines”). It goes into great detail (pages 15-27) about the EVAP testing that’s done and covers the various DTCs (Diagnostic Trouble Codes) like P0446 a bit too. Spoiler Alert: The primary automatic EVAP tests (on 2003 Fords) are done at highway speeds, so that may be a problem for your method of testing.

Disclaimer: I’m not a Torque expert. Having said that, I suspect that Torque is not going to help you very much here. You might monitor the Ford-specific Mode 22 PCM PID known as “EVAPCV” (“Evaporative Emissions Canister Purge Vent Control”, which shows the solenoid duty cycle, in percent, where 0% means “valve open”). It’s probably PID 1167 (hexadecimal) on your 2003 Expedition, in case you want to try to use Torque to monitor it. But, as you seem to understand quite well, you’d still need to trigger the PCM to exercise the vent solenoid and Torque isn’t going to be helpful in that regard. BTW, there’s also Ford-specific PCM Mode 22 PID “EVAPCVF” (“Evaporative Emissions Canister Purge Vent Fault” — a simple yes/no “flag”, probably PID 1630 [hex], bit 3).

FORScan (registered version only?) may be able to initiate the EVAP test, possibly allowing you to monitor the vent solenoid behavior when it runs, so it’s definitely worth investigating. (I’ve used FORScan but never to initiate an EVAP test.) FORScan will also undoubtedly have easier access to the other EVAP-related PIDs, at least compared to Torque. And FORScan is just generally a very useful program for Ford owners with even the simplest of scantool hardware.

I suspect that you may already know this, but, unfortunately, some of what ‘moreause’ says is misleading. DTC P0446 (on a 2003 Ford Expedition) is specifically for the EVAP vent solenoid, not for “the whole system” and, correspondingly, a leaky gas cap has nothing to do with your problem. Also, one simply cannot make blanket statements about Ford’s use of bus speeds (and/or protocols). Ford vehicles of that era (2003) often don’t have CAN-bus PCMs while newer Fords often support both the high-speed and medium-speed CAN bus/protocol. Your 2003 PCM probably uses the (SAE J1850) PWM bus/protocol (decidedly low speed at 41.6 Kbaud). Just curious — do you already own a scantool that can be used with Torque and/or FORScan?

Good luck in your diagnosis! Let me know if you need more info.

MechanicalFailure
Member
Posts: 2
Post Re: P0446 won
on: May 15, 2020 (GMT)

Tux,
Thanks for the document hint. I downloaded the document. Good information. I’m no expert. But, most of the detail I already understand. I’m at the point where I know the solenoid and wiring is good. I proved it with an external power supply. I am trying to confirm that the PCM is bad or something else is preventing the event from happening.

I do find one thing puzzling. It states “The Canister Vent Solenoid output circuit is checked for opens and shorts (P1451 or P0446)”. It actually states it a couple time in the document. I have not heard or read that it specifically is for shorts before.

Anyway, my Vent valve is about 60 ohms, which is in-range from the specs I have found. And there does not appear to be a short on the line to ground or power. If the PCM is ultimately at fault, maybe that is what they mean.

I do know the testing is done on the highway.

I can see through moreause’ comments.

I have a fairly generic adapter I am using with Torque Pro. While I get the gist of most of the functionality, I was hoping to get a glimpse of a pro’s perspective in trapping this issue, as well as possibly controlling the solenoid.

I will look into the ForScan app. I will also look into the Modes/PIDs that you mentioned. You’ve been quite helpful. Thanks!

Tux
Member
Posts: 8
Post Re: P0446 won
on: May 15, 2020 (GMT)

Glad to hear my info was somewhat helpful.

I forgot to mention the formula for the “EVAPCV” (1167) PID. I’m using

AB / 32768 * 100

where “AB” is the 1st 2 bytes treated as a single, unsigned, 16-bit value (i.e. ranging from 0 to 65535). (Convert that “formula” to whatever nomenclature makes Torque happy, assuming it doesn’t already support that PID in the Ford set.)

I concur with the confusion about P0446 being specifically for a shorted solenoid — it’s simply not very conclusive in any of the things I’ve read. Just to be safe, I would treat it as some sort of wiring issue (open or short) but it sounds like you’ve already considered that.

That Ford “obdsm307” document isn’t specific enough to tell, but I would surmise that if a P0446 (vent solenoid short circuit) is detected, the EVAP test might not even be commanded by the PCM — there doesn’t seem much point in running the test if the vent solenoid is uncontrollable. Pure speculation on my part, of course.

I saw something that said that the vent solenoid’s resistance should be “between 48 and 65 ohms”, so (FWIW) I concur that 60 ohms sounds good.

There are supposedly ways to initiate the EVAP test. It may be possible via OBD Service Mode 08 (“Request Control of On-Board System, Test or Component “), but I think Ford tends to use Modes 31-33 (“Perform Diagnostic Routine by Test Number”). (BTW, there should be a dollar-sign symbol in front of all those Mode numbers to indicate that they’re hexadecimal notation, but this crappy Torque forum software “eats” those characters up somehow!) The problem is that very few programs that I’ve encountered know anything about the commands to control an on-board system, like the EVAP system. FORScan is probably your best (low-cost) bet, from what I’ve seen.

Pages: [1]
WP-Forum by: Fredrik Fahlstad, Version: 2.4
Page loaded in: 0.115 seconds.

  Follow me on twitter