Check Engine Light on...code P0446

[miltont]

I was hoping that someone could help me out with my 2000 Amigo 3.2L V6.
My check engine light came on, and I went to autozone to get the code read. The code was P0446, "a malfunction in the electrical circuit for the vent control in the evap emission control system." I was wondering if this could be a simple fix...would cleaning the EGR valve do anything to get rid of this? Maybe this could help, but before the light came on, the amigo was taking awhile to start up (usually 4 cranks, with me pressing on the gas). And oh yeah, the check engine light didn't pop up until after I let the car sit for 12 days, while I was on vacation.

I also have a side problem...when I turned on my car for the first time after my vacation, besides the check engine light popping up for the first time, my ABS light also came on. I've tried the whole turning off, turning on the car and driving real slow process, but the light remains on. It just seems really interesting that both lights came on right after my car was sitting for awhile.

I'm thinking about taking the amigo to the dealership to get it checked out, but I wanted to see if anyone could offer some advice. Thanks!

[trooperbc]

Originally Posted by miltont

....The code was P0446, "a malfunction in the electrical circuit for the vent control in the evap emission control system." I was wondering if this could be a simple fix...would cleaning the EGR valve do anything to get rid of this? Maybe this could help, but before the light came on, the amigo was taking awhile to start up (usually 4 cranks, with me pressing on the gas). And oh yeah, the check engine light didn't pop up until after I let the car sit for 12 days, while I was on vacation.

the evap system is entirely different from the egr. and yes it could account for your rich starting. quickly, the evap system takes the excessive fuel vapors and redirects them to be burned by the engine at the appropriate time rather than escape into and pollute our air. it sounds like your evap system is either overloaded and/or dumping its charge into the engine at start up rather than waiting for the engine to warm up and do it other than idle.
it sounds like you are not too aware of what the evap system is, and might be at a loss to do any meaningful diagnosis yourself; but there is one thing you could check easily.
the evap cannister is that black small coffee-can-sized thing with hoses going into and out of. (mine is located in the eninge compartment near the air cleaner at the driver's side wheel well in my 1992 trooper; look around, you will find yours) on check these hoses. it's possible one or more have deteriated or come loose and this would affect the system's 'dumping' appropriateness.

i'd check the hoses and the things the hoses attach to, and then drive it for a couple of days to see if it clears itself up after it's 12-day hiatus (it's probably pissed off that you left it all alone )

hth

//bc

[miltont]

So I took the amigo into the dealer this week, and they finally called me back with a diagnosis on the check engine light. They said it was the fuel tank sensor. Is that the same thing as the fuel sending unit that people have been talking about? If so that's still covered on my 10y/120,000m powertrain warranty right? Right now they said it'll cost $370 to fix.

Also for the abs problem, they said it was the sensor on the front left disc. They wanted $290 to fix the problem, but I may tackle that problem myself. If anyone has any suggestions, it'll be much appreciated. It may take me awhile to start on this, but I don't think it'll be a problem to drive with one bad abs sensor...let me know if you think otherwise.

[Ramblin Fever]

Not 100% sure on your model year; but I've been driving w/o ABS for over 2yrs, sensor went out a 3rd time in less then 7yrs so I said forget it. Don't notice a difference, personally - not gonna fix it either, though I do get tired of the light.

[Canucklehead]

Originally Posted by miltont

So I took the amigo into the dealer this week, and they finally called me back with a diagnosis on the check engine light. They said it was the fuel tank sensor. Is that the same thing as the fuel sending unit that people have been talking about?

No, this isn't the same thing. If the dealer was correct your code was caused by the fuel tank pressure sensor. The main components that give Evap System code are thee Evap Canister, Fuel Tank Pressure Sensor or the Gas Cap (or the associated hoses).

[don9999]

My P0446 story:

I just solved a P0446 (EVAP Canister Vent Control Malfunction) on my 2001 Isuzu Trooper with 118k miles. It involved replacing the fuel tank pressure sensor without having to drop the tank.

Of course, for the record, I do not recommend in any way doing what I did and hereby disclaim any and all legal liability for any event occurring as a result of anyone performing the same or similar modifications as listed below.

She started throwing out a P0446. The OBD II scanning tool didn’t help much with diagnosis, as even the USB/software tool doesn’t display most of the sensor readings. No way I’m paying four grand for a Tech 2 scanner, so I proceeded to track it down blind.

Did the standard routine you see on the internet: check/clean/verify operation of vent solenoid, look for kinked tubing around the canister, make sure the canister blows freely, look for any evidence of cracks, restrictions, leaks, etc. No luck; solenoid valve worked great and everything else was fine too.

Isuzu manual diagnostic procedure says to hook up the Tech 2 and measure fuel tank pressure sensor voltage with the gas cap off (zero gauge pressure). The sensor is a 3-wire device: 5V reference, ground, signal out. It says signal out should be around 1.5V, and the total range of the sensor is 0.2 to 4.8 V. (At 4.5 in-H2O positive pressure, signal = 0.5 +/- 0.2V; at 14 in-H2O vacuum, signal = 4.5 +/- 0.2 V).

I traced down the signal and signal ground wires for the sensor to PCM on the schematic. After prying open the connector covers, finding the wires, sticking needles in them and connecting with test leads to the DMM, I found that the sensor signal was 4.80 V at all conditions. The tank pressure sensor was stuck in the high-vacuum position. SOB done failed.

Now, I’m sure you’re sitting there asking yourself, why the hell wasn’t she spitting out a P0453 (Fuel tank pressure sensor high voltage)? Well, as it turns out according to the manual, to set the P0453 the PCM has to detect 4.9V. I had 4.8V with a clearly-failed sensor. The software geeks have the alarm detect set too high to detect this failure (at least in my particular tolerance condition). Had I seen a P0453 initially, I wouldn’t have wasted all that time and effort trying to chase down a pseudo-P0446…

So, much to my chagrin, I am faced with the worst of all possible P0466 scenarios: dropping the fuel tank to replace the tank pressure sensor which is located at the fuel pump on top of the tank. And there’s 15 gallons in there now. Thinking about that job was a real buzz-harsher reality slam. I drank several beers and yet the problem stubbornly persisted.

But wait a minute, doesn’t one of those vent tubes come down off the top of the tank over to the EVAP canister? And isn’t it at the same pressure as the fuel tank, tank rollover valve be damned? How about just buying a new sensor and plumbing it into that line instead of dropping the tank and doing it the “right” way? The extra tube volume is nothing compared to the tank variation. The speed of the pressure wave is insignificant compared to the software test times (several seconds of measurement).

Got down under and scoped the scene. Found the three wires leading to the sensor, although some factory boob had reversed the color coding on the wires (signal and ground) from what they are at the PCM (which is correct per schematic). That threw me for a loop. After making it through that obstacle, I saw that the vent tube of interest is a simple ¼” ID fuel line. This project looks to involve machining up a custom manifold for the sensor to mate into, but still simpler than the sickening tank drop.

Wanting to do the job immediately, I hit up the local car parts shops for the sensor. Nobody had it but NAPA. They stock it for $48. Cheapest internet part, no doubt from China, is $35. Went down to NAPA and bought it along with ¼” fuel line and clamps. The OEM sensor was Japanese. This aftermarket part was made in New York by NAPA Echlin. I’m putting an aftermarket US-made part in a Japanese car. There is hope.

I saw that the pressure port has a gray rubber seal/bushing lightly bonded over (concentric to) the smaller internal fitting which is part of the main plastic housing. This is to fit/seal into the mating hole on the fuel pump assembly. Since I wasn’t putting it in there, I ripped that baby off and discovered a ¼” barb fitting hiding out, ready to use. No need to make a manifold, just plug that sucker right into the ¼” fuel line that I tee into. It couldn’t be simpler.

I didn’t want to use a plastic tee because of the possibility of cracking after long term exposure to gas fumes under stress. Went to Home Despot for a ¼” brass barbed hose tee. They didn’t have one, so I made it out of three brass ¼”x1/8” NPT barb fittings and a 1/8” NPT tee ($11 worth of tee). The upside of this highway robbery was it provided a good tie-wrap structure.

After soldering a couple feet of 3-wire cable to the three pins in the connector cavity of the sensor and testing operation with a 5VDC power supply and DMM (verifying 1.5V signal at ambient pressure), I potted the entire cavity with JB Quick Weld. Those solder joints will feel no pain. Then, using regular hose clamps and tie-wraps, I teed into the canister-to-tank vent hose, ran the third leg hose (about 10”) to the sensor, plugged/clamped the sensor into the end, and tie-wrapped everything strategically up and out of danger.

Then I ran the other end of the 3-wire cable over to the tank where I had earlier cut into the three wires from the PCM for test purposes (luckily, rather than just trusting the partly incorrect schematic). Made the three solder joints, using heat-shrink wrap to seal everything up. Tie-wrapped that all up.

The rest is history. No recurrence of the accursed P0446. She runs beautifully with proper emission control operation. Ready for smog check. Beats dropping the damn tank any day of the week.

[enslow]

Sorry to bring up an older thread, but I have some questions related to Don's diagnosis that are pertinant to my problem.

The P0446 is for Vent blocked, although the pressure sensor can fool the computer into thinking the vent is blocked if the pressure sensor says high pressure all the time, even when it's not.

Now to my question. When you tested the air flow through the canister, and through to the gas tank, how freely did the air flow? Could you blow out normally or was there some resistance? I, too, have found the vent is open, nothing kinked, no sign of any blockage.

[don9999]

I am happy to report that my fix is still working fine; no issues. As to your question, there was no significant resistance in the canister or to tank. It was like blowing thru a tube alone. There is no question that the P0466 was due to the failed tank pressure sensor.